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Are peptides safe? Side effects and risks
Authorized peptide drugs have known, documented side effects listed in their product monographs. Unauthorized "research" peptides add a second layer of risk: you can't know what's actually in the vial.
Risks Health Canada lists for unauthorized peptides
Health Canada's April 2026 advisory says people taking unauthorized peptide drugs are exposed to risks including:
- hormonal imbalance and mood swings
- blood sugar imbalance
- liver or kidney damage
- blood clots
- growth of cancerous tumours
It adds that unauthorized drugs may cause infections, allergic reactions and other serious complications; contain too much, too little or none of the active ingredient; contain unlisted or dangerous ingredients; be contaminated with solvents, heavy metals, particles (fibres, glass, plastic) or microbes (bacteria, fungi, endotoxins); be poorly labelled or stored; or interact with other medications.
Evidence gaps are a risk too
For many popular peptides (for example BPC-157, TB-500, Epitalon, MOTS-c), almost all research is in animals or cells. A 2026 sports-medicine review noted that rigorous human safety data for unapproved peptides are scarce and there is potential for serious harm.
Are peptides safer than steroids?
That comparison isn't supported by evidence. Peptides are a huge, varied group; some are well-studied drugs and many have no human safety data at all. Several are banned in sport by WADA.
What Health Canada advises
- Don't buy or use unauthorized drugs, including "research use only" products.
- Buy prescription drugs only from licensed pharmacies and check for an 8-digit DIN.
- If you used one and feel unwell, contact a physician, nurse practitioner or pharmacist.
- Dispose of products safely (municipal hazardous-waste guidance or a pharmacy) and report side effects to Health Canada.
Side effects and unknowns, peptide by peptide
Tap a peptide to see what's known about its side effects and what hasn't been studied. Each peptide's own page lists the sources.
AOD-9604
- Unknown quality and sterility of unauthorized products (see Health Canada's general peptide warnings).
Argireline and Other Cosmetic Peptides
- Generally well tolerated in studies; irritation possible.
BPC-157
- No clinical safety data in humans (Vasireddi 2025); adverse effects are possible from unregulated manufacturing and contamination.
- Health Canada's April 2026 advisory names BPC-157 and warns of infection, contamination and other risks of unauthorized injectables.
Cerebrolysin
- Non-fatal serious adverse events were higher with cerebrolysin in the Cochrane analysis (RR 2.39, moderate certainty). It is an injected animal-derived product.
CJC-1295
- Health Canada lists hormonal imbalance, blood sugar imbalance and growth of cancerous tumours among risks of unauthorized peptide drugs.
Collagen Peptides
- Generally well tolerated in trials. Check the source for allergies (e.g. fish for marine collagen).
Dihexa
- Human safety is unknown.
DSIP (Delta Sleep-Inducing Peptide)
- General risks of unauthorized injectables.
Epitalon (Epithalon)
- Unknown long-term human safety. General risks of unauthorized injectables.
GHK-Cu and Copper Peptides
- Topical: irritation is possible; patch-test new products. Injectable: Health Canada's warnings about unauthorized injectables apply.
GHRP-2 and GHRP-6
- Appetite increase (GHRP-6) and general risks of unauthorized injectables.
Hexarelin
- General risks of unauthorized injectables.
HGH Fragment 176-191
- All the general risks of unauthorized injectables apply: contamination, mislabelling and unknown content.
Humanin
- Human safety is unknown.
Insulin
- Hypoglycemia (low blood sugar) is the main serious risk, which is why insulin is used under medical supervision.
Ipamorelin
- Unknown long-term effects; general risks of unauthorized injectables.
Kisspeptin
- Hormonal effects; quality concerns for unauthorized products.
KPV
- Human safety unknown; unauthorized product risks.
Liraglutide
- Nausea and diarrhea were the most common adverse events in SCALE. Serious events occurred in 6.2% (liraglutide) vs 5.0% (placebo).
LL-37
- Topical trials reported it was well tolerated. Injected unauthorized products carry unknown risks.
Matrixyl (Palmitoyl Pentapeptide-4)
- Topical irritation is possible; patch-test. Cosmetic peptides are not for injection.
Melanotan I and II
- Published case reports describe renal infarction (Peters 2020), priapism (Dreyer 2019) and a melanoma case (Paurobally 2011) in people using melanotan. Case reports can't prove cause, but they are warning signs.
- A tan from melanotan doesn't replace sun protection.
MK-677 (Ibutamoren)
- The hip-fracture trial was terminated early due to a safety signal of congestive heart failure in a limited number of patients; the authors concluded it had an unfavourable safety profile in that population.
MOTS-c
- Unknown human safety; general risks of unauthorized injectables.
Oxytocin
- The injection is used under medical supervision. Nasal sprays sold online are not authorized products.
PT-141 (Bremelanotide)
- In the Phase 3 trials, nausea, flushing and headache were more common than with placebo (10% or more in both studies).
Retatrutide
- Health Canada's advisory lists general risks of unauthorized injectable peptides: too much, too little or none of the active ingredient, contamination (bacteria, endotoxins, heavy metals, particles), infection and allergic reactions.
Selank
- Unknown long-term safety; unverified online product quality.
Semaglutide
- In STEP 1, gastrointestinal side effects (nausea, diarrhea, vomiting, constipation) were the most common and usually mild to moderate; more people stopped treatment for GI events on semaglutide (4.5%) than placebo (0.8%).
- The product monograph lists further warnings and contraindications; your pharmacist or prescriber can review them for your situation.
Semax
- Long-term safety in healthy users is unknown; the quality of online products is unverified.
Sermorelin
- Quality concerns for unauthorized supplies; GH-axis effects.
SS-31 (Elamipretide)
- Injection-site reactions were the most common side effect; the FDA noted serious reactions have also been reported.
TB-500 and Thymosin Beta-4
- Health Canada's general warnings: contamination, infection, wrong content; it lists growth of cancerous tumours among risks of unauthorized peptides.
Tesamorelin
- Reported adverse events included joint and muscle pain, tingling (paresthesia) and injection-site reactions.
Thymosin Alpha-1
- Unauthorized supplies carry quality and sterility risks.
Tirzepatide
- Gastrointestinal effects were the most common adverse events in SURMOUNT-1; discontinuation due to adverse events was 4.3%–7.1% across tirzepatide groups vs 2.6% on placebo.
- The Zepbound monograph says not to combine it with other tirzepatide-containing products or other GLP-1 receptor agonists.