Peptide Science Desk

Peptide side effects: what is common and what is serious?

Known for approved drugs. Unknown for most others.

FDA labels list side effects for approved peptide drugs. Most online peptides were barely tested.

By the Peptide Science Desk Editorial TeamFact-checked against FDA and official sources · Not yet reviewed by a licensed clinician. How we check facts

Short answer: It depends on the peptide. For approved GLP-1 peptide drugs like Wegovy and Zepbound, FDA labels say the most common side effects are stomach problems: nausea, diarrhea, vomiting and constipation. Less common but serious risks include pancreatitis and gallbladder problems. For BPC-157 and most peptides sold online, side effects in people are mostly unknown, because they were barely tested. New to peptides? Start here: what are peptides?
A pharmacist in a white coat looks at a bottle of liquid medicine in front of shelves
A pharmacist checks a liquid medicine (1988 photo).Photo: Bill Branson, National Cancer Institute (NIH), public domain

Peptide side effects checker

Turn on JavaScript to switch medicines. Every medicine is also listed further down this page.

GLP-1: Wegovy (semaglutide shot or pill)FDA label
  • FDA statusFDA approved
  • Proof it worksStrong for its approved uses
  • Safety dataWell studied

Used for: Weight loss and lower heart risk in adults with obesity or overweight (plus a liver disease use for the shot)

Most common side effects (FDA label)

  • nausea
  • diarrhea
  • vomiting
  • constipation
  • belly pain
  • headache
  • tiredness
  • upset stomach
  • dizziness
  • bloating
  • burping
  • gas
  • stomach flu
  • heartburn
  • hair loss

Serious warnings on the label

  • Boxed warning: caused thyroid C-cell tumors in rats or mice. Nobody knows if this happens in people.
  • Pancreatitis (swelling of the pancreas)
  • Gallbladder problems
  • Kidney injury from dehydration (from vomiting or diarrhea)
  • Serious allergic reactions
  • Low blood sugar, mainly with insulin or a sulfonylurea pill
  • Eye problems in some people with type 2 diabetes
  • Food in the lungs during surgery or sedation: tell your surgeon you take it

Alcohol

No special alcohol warning on the FDA label (checked Oct 22, 2026). The label does warn about pancreatitis, and NIH (NIDDK) says heavy drinking is a common cause of pancreatitis.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

Or start with a symptom

See which approved drugs in this tool list it as a most common side effect on their FDA label.

This is not a diagnosis. FDA status, proof and safety data are rated separately. Little safety data means risks are unknown, not that a peptide fails. We never share doses or link research-peptide sellers.

Stomach side effects on Zepbound

Stomach side effects on Zepbound (tirzepatide)

% of adults with each problem, by dose, in the weight-loss trials

Wegovy and Zepbound numbers come from different trials. Do not compare them directly.

Show the numbers as a table
Stomach side effects on Zepbound (tirzepatide): % of adults with each problem, by dose, in the weight-loss trials
Side effect5 mg (630)10 mg (948)15 mg (941)Placebo (958)
Nausea25%29%28%8%
Diarrhea19%21%23%8%
Vomiting8%11%13%2%
Constipation17%14%11%5%
From the Zepbound FDA label, section 6.1, Table 1. Numbers in brackets are how many adults got each dose. Sources: Zepbound FDA label, section 6.1, Table 1 (DailyMed).

Side effects list for every medicine in this tool

Tap a name to open it. Same facts as the checker above.

GLP-1: Wegovy (semaglutide shot or pill)
GLP-1: Wegovy (semaglutide shot or pill)FDA label
  • FDA statusFDA approved
  • Proof it worksStrong for its approved uses
  • Safety dataWell studied

Used for: Weight loss and lower heart risk in adults with obesity or overweight (plus a liver disease use for the shot)

Most common side effects (FDA label)

  • nausea
  • diarrhea
  • vomiting
  • constipation
  • belly pain
  • headache
  • tiredness
  • upset stomach
  • dizziness
  • bloating
  • burping
  • gas
  • stomach flu
  • heartburn
  • hair loss

Serious warnings on the label

  • Boxed warning: caused thyroid C-cell tumors in rats or mice. Nobody knows if this happens in people.
  • Pancreatitis (swelling of the pancreas)
  • Gallbladder problems
  • Kidney injury from dehydration (from vomiting or diarrhea)
  • Serious allergic reactions
  • Low blood sugar, mainly with insulin or a sulfonylurea pill
  • Eye problems in some people with type 2 diabetes
  • Food in the lungs during surgery or sedation: tell your surgeon you take it

Alcohol

No special alcohol warning on the FDA label (checked Oct 22, 2026). The label does warn about pancreatitis, and NIH (NIDDK) says heavy drinking is a common cause of pancreatitis.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

GLP-1: Ozempic (semaglutide shot)
GLP-1: Ozempic (semaglutide shot)FDA label
  • FDA statusFDA approved
  • Proof it worksStrong for its approved uses
  • Safety dataWell studied

Used for: Blood sugar in adults with type 2 diabetes, plus heart and kidney risk uses on its label

Most common side effects (FDA label)

  • nausea
  • vomiting
  • diarrhea
  • belly pain
  • constipation

Serious warnings on the label

  • Boxed warning: caused thyroid C-cell tumors in rats or mice. Nobody knows if this happens in people.
  • Pancreatitis (swelling of the pancreas)
  • Gallbladder problems
  • Kidney injury from dehydration (from vomiting or diarrhea)
  • Serious allergic reactions
  • Low blood sugar, mainly with insulin or a sulfonylurea pill
  • Eye problems in some people with type 2 diabetes
  • Food in the lungs during surgery or sedation: tell your surgeon you take it

Alcohol

No special alcohol warning on the FDA label (checked Oct 22, 2026). The label does warn about pancreatitis, and NIH (NIDDK) says heavy drinking is a common cause of pancreatitis. With insulin or a sulfonylurea, NIDDK says alcohol without enough food can cause low blood sugar and hide its signs.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

GLP-1: Rybelsus or Ozempic tablets (semaglutide pills)
GLP-1: Rybelsus or Ozempic tablets (semaglutide pills)FDA label
  • FDA statusFDA approved
  • Proof it worksStrong for its approved uses
  • Safety dataWell studied

Used for: Blood sugar in adults with type 2 diabetes, and lower heart risk

Most common side effects (FDA label)

  • nausea
  • belly pain
  • diarrhea
  • less hunger
  • vomiting
  • constipation

Serious warnings on the label

  • Boxed warning: caused thyroid C-cell tumors in rats or mice. Nobody knows if this happens in people.
  • Pancreatitis (swelling of the pancreas)
  • Gallbladder problems
  • Kidney injury from dehydration (from vomiting or diarrhea)
  • Serious allergic reactions
  • Low blood sugar, mainly with insulin or a sulfonylurea pill
  • Eye problems in some people with type 2 diabetes
  • Breastfeeding is not recommended (an added ingredient, SNAC, may build up in babies)

Alcohol

No special alcohol warning on the FDA label (checked Oct 22, 2026). The label does warn about pancreatitis, and NIH (NIDDK) says heavy drinking is a common cause of pancreatitis. With insulin or a sulfonylurea, NIDDK says alcohol without enough food can cause low blood sugar and hide its signs.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

GLP-1: Zepbound (tirzepatide)
GLP-1: Zepbound (tirzepatide)FDA label
  • FDA statusFDA approved
  • Proof it worksStrong for its approved uses
  • Safety dataWell studied

Used for: Weight loss in adults with obesity or overweight, and sleep apnea with obesity

Most common side effects (FDA label)

  • nausea
  • diarrhea
  • vomiting
  • constipation
  • belly pain
  • upset stomach
  • injection site reactions
  • tiredness
  • allergic reactions
  • burping
  • hair loss
  • heartburn

Serious warnings on the label

  • Boxed warning: caused thyroid C-cell tumors in rats or mice. Nobody knows if this happens in people.
  • Pancreatitis (swelling of the pancreas)
  • Gallbladder problems
  • Kidney injury from dehydration (from vomiting or diarrhea)
  • Serious allergic reactions
  • Low blood sugar, mainly with insulin or a sulfonylurea pill
  • Eye problems in some people with type 2 diabetes
  • Food in the lungs during surgery or sedation: tell your surgeon you take it
  • May make birth control pills work less well for a while

Alcohol

No special alcohol warning on the FDA label (checked Oct 22, 2026). The label does warn about pancreatitis, and NIH (NIDDK) says heavy drinking is a common cause of pancreatitis.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

GLP-1: Mounjaro (tirzepatide)
GLP-1: Mounjaro (tirzepatide)FDA label
  • FDA statusFDA approved
  • Proof it worksStrong for its approved use
  • Safety dataWell studied

Used for: Blood sugar in adults with type 2 diabetes

Most common side effects (FDA label)

  • nausea
  • diarrhea
  • less hunger
  • vomiting
  • constipation
  • upset stomach
  • belly pain

Serious warnings on the label

  • Boxed warning: caused thyroid C-cell tumors in rats or mice. Nobody knows if this happens in people.
  • Pancreatitis (swelling of the pancreas)
  • Gallbladder problems
  • Kidney injury from dehydration (from vomiting or diarrhea)
  • Serious allergic reactions
  • Low blood sugar, mainly with insulin or a sulfonylurea pill
  • Eye problems in some people with type 2 diabetes
  • Food in the lungs during surgery or sedation: tell your surgeon you take it
  • May make birth control pills work less well for a while

Alcohol

No special alcohol warning on the FDA label (checked Oct 22, 2026). The label does warn about pancreatitis, and NIH (NIDDK) says heavy drinking is a common cause of pancreatitis. With insulin or a sulfonylurea, NIDDK says alcohol without enough food can cause low blood sugar and hide its signs.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

GLP-1: Saxenda (liraglutide)
GLP-1: Saxenda (liraglutide)FDA label
  • FDA statusFDA approved
  • Proof it worksStrong for its approved use
  • Safety dataWell studied

Used for: Weight loss in people with obesity or overweight

Most common side effects (FDA label)

  • nausea
  • diarrhea
  • constipation
  • vomiting
  • injection site reactions
  • headache
  • low blood sugar
  • upset stomach
  • tiredness
  • dizziness
  • belly pain
  • fever
  • stomach flu

Serious warnings on the label

  • Boxed warning: caused thyroid C-cell tumors in rats or mice. Nobody knows if this happens in people.
  • Pancreatitis (swelling of the pancreas)
  • Gallbladder problems
  • Kidney injury from dehydration (from vomiting or diarrhea)
  • Serious allergic reactions
  • Low blood sugar, mainly with insulin or a sulfonylurea pill
  • Eye problems in some people with type 2 diabetes
  • Food in the lungs during surgery or sedation: tell your surgeon you take it
  • Faster heart rate

Alcohol

No special alcohol warning on the FDA label (checked Oct 22, 2026). The label does warn about pancreatitis, and NIH (NIDDK) says heavy drinking is a common cause of pancreatitis.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

GLP-1 pill: Foundayo (orforglipron, not a peptide)
GLP-1 pill: Foundayo (orforglipron, not a peptide)FDA label
  • FDA statusFDA approved
  • Proof it worksStrong for its approved use
  • Safety dataStudied (newer drug)

Used for: Weight loss in adults with obesity or overweight

Most common side effects (FDA label)

  • nausea
  • constipation
  • diarrhea
  • vomiting
  • upset stomach
  • belly pain
  • headache
  • bloating
  • tiredness
  • burping
  • heartburn
  • gas
  • hair loss

Serious warnings on the label

  • Boxed warning about thyroid C-cell tumors seen with GLP-1 drugs in rodents
  • Pancreatitis
  • Severe stomach problems
  • Kidney injury from dehydration
  • Low blood sugar, mainly with insulin or a sulfonylurea pill
  • Serious allergic reactions
  • Gallbladder problems

Alcohol

No special alcohol warning on the FDA label (checked Oct 22, 2026). The label does warn about pancreatitis, and NIH (NIDDK) says heavy drinking is a common cause of pancreatitis.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

Vyleesi (bremelanotide, PT-141)
Vyleesi (bremelanotide, PT-141)FDA label
  • FDA statusFDA approved
  • Proof it worksSome, for its approved use
  • Safety dataStudied

Used for: Low sexual desire with distress in women before menopause

Most common side effects (FDA label)

  • nausea
  • flushing
  • injection site reactions
  • headache
  • vomiting

Serious warnings on the label

  • Blood pressure goes up and heart rate goes down for some hours after each dose
  • Not recommended for people at high risk of heart disease
  • Dark patches on the skin, face or gums (1% in trials; did not always go away)
  • Nausea can be strong at first; most people did better by the second dose

Alcohol

Tested. In a label study with about 3 drinks, alcohol did not change how much drug got into the blood. Flushing was about as common as with the drug alone, and headache about as common as with alcohol alone.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

Egrifta SV (tesamorelin)
Egrifta SV (tesamorelin)FDA label
  • FDA statusFDA approved
  • Proof it worksStrong for its approved use
  • Safety dataStudied

Used for: Less deep belly fat in adults with HIV

Most common side effects (FDA label)

  • joint pain
  • redness at the injection site
  • itching at the injection site
  • pain in arms or legs
  • swollen legs or feet
  • muscle pain

Serious warnings on the label

  • Raises IGF-1, a growth factor: not for people with active cancer
  • Fluid build-up, including carpal tunnel syndrome
  • High blood sugar or diabetes can start
  • Serious allergic reactions
  • Must not be used in pregnancy

Alcohol

No alcohol warning found on the FDA label (checked Oct 22, 2026).

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

Forteo (teriparatide)
Forteo (teriparatide)FDA label
  • FDA statusFDA approved
  • Proof it worksStrong for its approved use
  • Safety dataWell studied

Used for: Weak bones (osteoporosis) with a high chance of breaking a bone, including after menopause

Most common side effects (FDA label)

  • joint pain
  • pain
  • nausea

Serious warnings on the label

  • Serious allergic reactions
  • Bone cancer (osteosarcoma) concern: not for people at higher risk
  • Not for people who already have a high blood calcium problem

Alcohol

No alcohol warning found on the FDA label (checked Oct 22, 2026).

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

Tymlos (abaloparatide)
Tymlos (abaloparatide)FDA label
  • FDA statusFDA approved
  • Proof it worksStrong for its approved use
  • Safety dataWell studied

Used for: Weak bones (osteoporosis) with a high chance of breaking a bone, including after menopause

Most common side effects (FDA label)

  • extra calcium in the urine
  • dizziness
  • nausea
  • headache
  • pounding heartbeat
  • tiredness
  • upper belly pain
  • spinning feeling

Serious warnings on the label

  • Serious allergic reactions
  • Bone cancer (osteosarcoma) concern: not for people at higher risk
  • Dizziness or low blood pressure when standing after a dose: sit or lie down

Alcohol

No alcohol warning found on the FDA label (checked Oct 22, 2026).

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

GLP-1: Retatrutide ("GLP-3")
GLP-1: Retatrutide ("GLP-3")Study
  • FDA statusIn testing, not FDA approved
  • Proof it worksSome (big trials still running)
  • Safety dataLimited: about 900 people in published trials

Used for: Weight loss (still in trials)

Side effects

  • Stomach problems like nausea were most common in early trials, mostly mild to medium

What is known about risks

  • Heart rate went up with higher doses in an early trial
  • Long-term risks not known yet
  • "Research" retatrutide sold online is of unknown quality, the FDA says

Alcohol

No alcohol studies found.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

BPC-157
BPC-157Study
  • FDA statusNot FDA approved
  • Proof it worksEarly: small studies only
  • Safety dataVery little: about 30 people, for a short time

Used for: Sold for healing injuries and pain

Side effects

  • Unknown. Not enough studies in people to list side effects.

What is known about risks

  • Long-term risks are unknown
  • Products sold "for research" are not checked by the FDA

Alcohol

No alcohol studies found.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

TB-500
TB-500Our page
  • FDA statusNot FDA approved
  • Proof it worksAnimal or lab studies only
  • Safety dataNo published safety data for TB-500 shots in people

Used for: Sold for muscle and injury recovery

Side effects

  • Unknown. Not enough studies in people to list side effects.

What is known about risks

  • Risks are unknown
  • Banned in sports by WADA

Alcohol

No alcohol studies found.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

CJC-1295
CJC-1295Our page
  • FDA statusNot FDA approved
  • Proof it worksEarly: small studies only
  • Safety dataOnly a small group of healthy adults, for weeks

Used for: Sold for muscle, fat loss or anti-aging

Side effects

  • Unknown. Not enough studies in people to list side effects.

What is known about risks

  • Long-term risks are unknown

Alcohol

No alcohol studies found.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

Ipamorelin
IpamorelinOur page
  • FDA statusNot FDA approved
  • Proof it worksNo studies in people found
  • Safety dataAbout 114 hospital patients for up to 7 days, not the way people use it now

Used for: Sold for muscle, sleep or anti-aging

Side effects

  • Unknown. Not enough studies in people to list side effects.

What is known about risks

  • Long-term risks are unknown

Alcohol

No alcohol studies found.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

GHK-Cu (copper peptide shots)
GHK-Cu (copper peptide shots)Our page
  • FDA statusNot FDA approved as a drug
  • Proof it worksEarly: small studies only
  • Safety dataVery little data on shots in people, says the FDA

Used for: Sold for younger-looking skin

Side effects

  • Unknown. Not enough studies in people to list side effects.

What is known about risks

  • Shots and creams are very different products. Creams are sold as cosmetics.

Alcohol

No alcohol studies found.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

Semax or Selank (nasal sprays)
Semax or Selank (nasal sprays)Our page
  • FDA statusNot FDA approved
  • Proof it worksEarly: small studies only
  • Safety dataVery little safety data in people, says the FDA

Used for: Sold for focus, memory, stress and worry

Side effects

  • Unknown. Not enough studies in people to list side effects.

What is known about risks

  • Risks are unknown

Alcohol

No alcohol studies found.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

MK-677 (ibutamoren, not a peptide)
MK-677 (ibutamoren, not a peptide)Our page
  • FDA statusNot FDA approved
  • Proof it worksMixed results
  • Safety dataHundreds of people; a trial stopped early for a heart failure warning sign

Used for: Sold for muscle and growth hormone

Side effects

  • Unknown. Not enough studies in people to list side effects.

What is known about risks

  • A trial stopped early for a heart failure warning sign
  • Banned in sports by WADA

Alcohol

No alcohol studies found.

Get help right away for severe belly pain that may spread to your back, swelling of the face or throat, or trouble breathing. Call 911 in an emergency.

Each medicine card links its own FDA label or study. Lists checked October 22, 2026. Checker sources: DailyMed: FDA drug labels (Wegovy, Ozempic, Rybelsus, Zepbound, Mounjaro, Saxenda, Foundayo, Vyleesi, Egrifta SV, Forteo, Tymlos), checked Oct 22, 2026 · FDA: MedWatch, report a problem · NIDDK (NIH): Symptoms and causes of pancreatitis · NIDDK (NIH): Low blood glucose (hypoglycemia) · PubMed: Jastreboff et al., Retatrutide phase 2 trial, NEJM 2023 · PubMed: Poolton et al., Human evidence for BPC-157: a systematic review, 2026 · FDA: Concerns with unapproved GLP-1 drugs used for weight loss

What are the most common side effects of peptides?

  • Each peptide is a different drug, so side effects differ.
  • Wegovy (semaglutide): the label lists nausea, diarrhea, vomiting, constipation, belly pain, headache, tiredness, upset stomach, dizziness, bloating, burping, gas, heartburn and hair loss among the most common.
  • Zepbound (tirzepatide): the label lists nausea, diarrhea, vomiting, constipation, belly pain, upset stomach, injection site reactions, tiredness, allergic reactions, burping, hair loss and heartburn.
  • Vyleesi (PT-141): nausea, flushing, injection site reactions, headache and vomiting.
  • Egrifta SV (tesamorelin): joint pain and redness at the injection site are among the most common.
  • BPC-157, TB-500 and most online peptides: unknown. They were barely tested in people.

Can peptides cause acne, headaches or anxiety?

  • Headache: yes for some. It is on the most common list for Wegovy and Vyleesi.
  • Acne: we did not find acne on the most common lists of the labels we checked (Wegovy, Zepbound, Vyleesi, Egrifta SV, Forteo).
  • Anxiety and mood swings: we did not find them on those most common lists either.
  • Vyleesi can cause dark patches on the skin, such as the face or gums. The label says this happened in 1% of people in trials, and it did not always go away.
  • For unapproved peptides, nobody has checked well enough to say.

Do peptides cause hair loss?

  • Some do. Hair loss is on the most common side effect list for Wegovy, Zepbound and the GLP-1 pill Foundayo.
  • Tell your doctor if you notice more hair coming out.
  • For unapproved peptides, there is no good data either way.

Can peptides cause constipation, diarrhea or other stomach problems?

  • Yes, GLP-1 peptide drugs often do. Their labels say stomach side effects can sometimes be severe.
  • The labels say they are not recommended for people with severe gastroparesis (a very slow stomach).
  • Throwing up or diarrhea can dry you out. The labels warn this can hurt your kidneys. Drink fluids and call your doctor if it does not stop.
  • In the STEP 1 trial, nausea and diarrhea were usually mild to medium and faded with time.

What are the serious side effects of peptides?

  • GLP-1 labels (Wegovy, Zepbound, Saxenda) have a boxed warning: these drugs caused thyroid tumors in rats or mice. Nobody knows if this happens in people.
  • The labels also warn about pancreatitis, gallbladder problems, kidney injury from dehydration, serious allergic reactions, and eye problems in some people with type 2 diabetes.
  • Low blood sugar is more likely if you also take insulin or a sulfonylurea pill.
  • Food can stay in the stomach longer. The labels say to tell your doctor before any surgery or sedation, because food could get into the lungs.
  • Vyleesi makes blood pressure go up for a few hours after each dose. It is not recommended for people at high risk of heart disease.

Can you drink alcohol on peptides?

  • We searched the FDA labels for Wegovy, Zepbound, Mounjaro, Saxenda and the semaglutide pills. We found no special alcohol warning. The word "alcohol" there is about swabs and inactive ingredients.
  • That does not make heavy drinking safe. The labels warn about pancreatitis, and NIDDK (NIH) says heavy alcohol use is one of the most common causes of pancreatitis.
  • If you have diabetes and use insulin or a sulfonylurea, NIDDK says alcohol without enough food can cause low blood sugar and can hide its early signs.
  • Vyleesi (PT-141): the label describes a study with about 3 drinks. Alcohol did not change how much drug got into the blood. Flushing was about as common as with the drug alone. Headache was about as common as with alcohol alone.
  • Unapproved peptides: we found no alcohol studies. Ask your doctor or pharmacist about your own case.

Are there long-term side effects of peptides?

  • Many approved peptide drugs were tested in big trials that lasted more than a year, and the FDA keeps collecting reports after approval.
  • The thyroid tumor warning on GLP-1 labels comes from animal studies. Human risk is still unknown.
  • For most online peptides, there is no long-term data in people at all. Unknown is not the same as safe.

What should I do if I have a side effect?

  • Call your doctor or pharmacist. Do not just stop a prescribed medicine without asking, unless they tell you to.
  • Get care right away for severe belly pain that may spread to your back, with or without vomiting. NIDDK says this can be a sign of pancreatitis.
  • Call 911 for swelling of the face, lips or throat, or trouble breathing.
  • You can report a side effect to FDA MedWatch online or at 1-800-FDA-1088. MedWatch takes reports from the public.

The numbers in charts

Stomach side effects on Wegovy (semaglutide 2.4 mg)

% of adults with each problem in the weight-loss trials

Most were mild to moderate and happened while the dose was going up.

Show the numbers as a table
Stomach side effects on Wegovy (semaglutide 2.4 mg): % of adults with each problem in the weight-loss trials
Side effectWegovy (2,116 adults)Placebo (1,261 adults)
Nausea44%16%
Diarrhea30%16%
Vomiting24%6%
Constipation24%11%
From the Wegovy FDA label, section 6.1, Table 3. Sources: Wegovy FDA label, section 6.1, Table 3 (DailyMed).

Stomach side effects on semaglutide pills

% of adults with any stomach or gut side effect (like nausea or diarrhea)

Many people on placebo also had stomach problems. Most were mild to moderate.

Show the numbers as a table
Stomach side effects on semaglutide pills: % of adults with any stomach or gut side effect (like nausea or diarrhea)
TrialSemaglutide pillPlacebo
OASIS 1 (50 mg pill)
667 adults · 68 weeks		80%46%
OASIS 4 (25 mg pill, Wegovy tablets)
307 adults · 64 weeks		74.0%42.2%
Two separate trials. Paid for by Novo Nordisk, which makes semaglutide. Sources: Knop et al., Lancet 2023 (OASIS 1) (PMID 37385278); Wharton et al., NEJM 2025 (OASIS 4) (PMID 40934115).

Vyleesi (bremelanotide, PT-141) side effects

% of women with each side effect in the 2 main trials

18% of women on Vyleesi stopped because of side effects, vs 2% on placebo.

Show the numbers as a table
Vyleesi (bremelanotide, PT-141) side effects: % of women with each side effect in the 2 main trials
Side effectVyleesi (627 women)Placebo (620 women)
Nausea40.0%1.3%
Flushing (red, warm face)20.3%0.3%
Shot-site reactions13.2%8.4%
Headache11.3%1.9%
Vomiting4.8%0.2%
RECONNECT trials: 1,267 women were picked at random; 1,247 got at least one dose and were counted for side effects. From the FDA label, Table 1. Sources: Vyleesi FDA label, section 6.1, Table 1 (DailyMed); Kingsberg et al., Obstet Gynecol 2019 (RECONNECT) (PMID 31599840).

More charts: Peptides by the numbers

Side effects on FDA labels at a glance

Wegovy (semaglutide)Zepbound (tirzepatide)Vyleesi (PT-141)BPC-157, TB-500 (not approved)
Most commonNausea, diarrhea, vomiting, constipation, belly pain, headache, tirednessNausea, diarrhea, vomiting, constipation, belly pain, injection site reactions, tirednessNausea, flushing, injection site reactions, headache, vomitingUnknown
Hair loss on common list?YesYesNoUnknown
Serious warningsThyroid tumors in rodents (boxed), pancreatitis, gallbladder, kidneys, allergySame kinds of warningsShort rise in blood pressure; dark skin patchesUnknown
Alcohol on the labelNo special warning foundNo special warning foundStudied: alcohol did not change drug levelsNo studies found
Check any peptide in 1 secondFree FDA Status Checker: approved, being tested, or not proven.

FAQ

Do peptide side effects go away?

Often, for stomach effects. The Vyleesi label says nausea got better for most people by the second dose. Tell your doctor if a side effect is bad or lasts.

Is it normal to feel tired on a GLP-1 drug?

Tiredness (fatigue) is on the common lists for Wegovy and Zepbound. Tell your doctor, since there can be other causes.

Can peptides cause heartburn?

Yes, for some. Heartburn (reflux) and upset stomach are on the common lists for Wegovy and Zepbound.

Does BPC-157 have side effects?

The 2026 review found no treatment-related side effects in its 3 small studies. But they had only 30 people and were poor quality, which is far too few to know.

Can I report a problem with a peptide I bought online?

Yes. FDA MedWatch takes reports about medicines and cosmetics from the public. Keep the package and lot number.

Are side effects worse with compounded versions?

The FDA says unapproved and compounded versions are not checked by the FDA for safety, quality or strength before sale. Some compounded GLP-1s were recalled in 2026 over sterility. Use our recall checker.

Where do these side effect lists come from?

From the "most common adverse reactions" part of each FDA drug label on DailyMed, checked October 22, 2026. For unapproved peptides, the safety line comes from our peptide pages.

Why does the list for my peptide say unknown?

Because good studies in people do not exist yet. Unknown does not mean safe. It also does not mean the peptide fails to work.

Does a longer list mean a drug is more dangerous?

No. Approved drugs were tested in many people, so more side effects were written down. A short list can just mean fewer tests.

Should I stop my peptide if I get side effects?

Call your doctor or pharmacist first, unless it is an emergency. Some side effects fade with time. Others need care right away. Our checker does not diagnose anything.

Can I use this checker for my pet?

No. These lists are from human drug labels. Ask a veterinarian.

Related pages

We never share doses or tell you where to buy. Always ask your doctor. Print our doctor questions sheet.

Sources

Not medical advice. Medical disclaimer.