Limited human dataNot FDA approved

Melanotan II side effects

Also known as: MT-2 · MT2 · MT-II · Melanotan 2 · MT 2

Updated Oct 24, 202649 sources

13 side effects reported for Melanotan II: 10 from studies and labels, 3 from users and guides. 4 come with the ways people manage them.

Melanotan II overview

Side effects reported in studies and labels

Rates as each trial or label states them. A rate from one trial does not carry over to research-grade vials or other doses.

From trials and regulators10

Clinical studies and regulatory documents.

Nausea (trials)
Mild nausea at most doses in the phase I trial. In the ED trials at 0.025 mg/kg, 12.9% had severe nausea (4 of 19 injections in one trial).
How people manage it
- In the phase I trial no one needed an anti-nausea drug.
Spontaneous erections, stretching and yawning
Seen in the phase I and ED trials: erections came and went for 1 to 5 hours after a dose, often with a stretching and yawning spell.
Lower appetite
Reported more often after MT-II than placebo in the 1998 ED trial; none needed treatment.
Drowsiness and fatigue
At 0.03 mg/kg, one of two men in the phase I trial had grade II somnolence and fatigue.
Darker moles and new moles (case reports)
Case reports describe existing moles darkening and new, sometimes atypical, moles appearing, in one case 24 hours after a single dose. No study gives a rate.
Melanoma (case reports)
Four case reports describe melanoma arising in existing moles during or soon after melanotan use. A causal link is not proven; several cases also involved heavy sunbed use.
Priapism
Rare: a 2021 case report was the third in the literature and needed surgery.
Toxicity and muscle breakdown after a large dose
One case after a 6 mg injection, six times the recommended starting dose, the patient said: racing heart, agitation, rhabdomyolysis and kidney strain; he recovered after ICU care.
Renal infarction
Single case report; rare.
Serious events in case reports (FDA summary)
FDA's compounding review cites published case reports of melanoma, posterior reversible encephalopathy syndrome (PRES), sympathomimetic toxidrome and priapism. No rates are given.

Side effects users and guides report

What people post and what dosing guides list. These are reports, not measured rates.

From users and guides3

Community reports, competitor and vendor guides, media.

Nausea (community)
The most discussed side effect on r/Melanotan2. One guide claims 80 to 90% of users in loading, without a source. It usually eases within the first week of daily dosing.
How people manage it
- Start at 100 to 250 mcg and step up slowly.
- Inject at bedtime to sleep through the peak, 30 to 90 minutes after the shot.
- Users take ondansetron (Zofran, prescription) about 20 minutes before, or a non-drowsy antihistamine about 15 minutes before; some found ondansetron did little.
- One user found a motion-sickness tablet (meclizine) worked better than antihistamines.
Facial flushing
Common in loading: a warm flush of the face and chest 10 to 30 minutes after the shot, usually gone within an hour.
How people manage it
- Antihistamine pre-treatment and evening dosing, per one guide and user reports.
Darker moles, freckles and lips (community)
Commonly reported on r/Melanotan2: darker moles and freckles, new small dots on the face, and darker lips or knuckles. Some say marks fade with the tan.
How people manage it
- Photograph moles before starting and every 2 to 4 weeks, per one guide.
- Users who disliked new freckles lowered the dose or switched to MT1.

Who should avoid it, and what not to combine

Personal or family history of melanomaCondition
Case reports link MT-II use to mole changes and melanoma; guides say people with prior skin cancer or a strong family history should avoid it.
Many or atypical molesCondition
MT-II darkens existing moles and can trigger new ones, which makes a real warning sign easier to miss.
Heart disease or uncontrolled blood pressureCondition
Guides cite flushing, blood pressure changes and transient blood pressure rises through MC4R.
History of priapism or sickle cell traitCondition
Priapism has been reported after MT-II, so anyone with a higher baseline risk is told to avoid it.
Pregnancy and breastfeedingCondition
No human safety data exist for these groups.
Other melanocortin agonists such as PT-141Substance
They hit the same receptors, so combining them adds side effects; one guide says avoid, another lists them as a separate-vial stack.
GLP-1 drugs (semaglutide and similar)Substance
Both cause nausea. One r/Melanotan2 user who raised MT2 while starting semaglutide reported a week of vomiting despite ondansetron.

How much is known

Limited human data

Human data are small 1990s trials: a 3-man phase I tanning study and ED crossover trials of 10 men each (20 combined), all at about 0.01 to 0.03 mg/kg. They showed tanning, erections and frequent nausea. Safety beyond that rests on case reports (moles, melanoma, priapism, rhabdomyolysis). Community doses of 100 to 500 mcg were never trialled. A 2026 phase 2 vitiligo registry record exists, but its summary calls itself an example record.