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Cyclic melanocortin receptor agonist (research compound) · safety
Melanotan II side effects
The melanotan ii side effects reported most often are nausea, drowsiness and tiredness and spontaneous erections. The full list is below, with the cited trial report cited at the bottom of the page.
Rarer, but worth being able to spot: priapism, rhabdomyolysis and kidney infarction, and 2 more in the table below.
The sources describe these effects in relation to the dose and to the early weeks.
Melanotan II is a ring of seven amino acids. It copies a hormone the body already uses to tell skin cells to make more of the brown pigment that darkens a tan. People take it to tan faster and darker, usually alongside sunbeds or sun. A second, unadvertised reason is that it causes erections, which is why some men take it too.
One human trial exists, from 1996, in three men. It reported darker skin in two of them. It was a safety study, not a tanning study, and nothing followed it. The erections were not a stray finding either. That trial reported them, and a different molecule was later built from this one for that use alone.
At a glance
Common reactions listed
3
Serious reactions listed
5
Boxed warning
No label exists
Strongest source
limited human data
Common reactions
The full list, as reported across the available trial evidence. There is no approved label to read frequency bands off, so these are the trials’ own figures.
| Reaction | Frequency |
|---|---|
| Nausea | Mild, at most dose levels in the 1996 trial, and not severe enough in any subject to need treatment for it |
| Drowsiness and tiredness | Graded moderate in one of the two subjects who reached 0.03 mg/kg — the finding that set the trial’s recommended dose one step lower |
| Spontaneous erections | Intermittently for one to five hours after a dose in the 1996 trial, longer at higher doses. A stretching and yawning complex tracked the onset |
Serious reactions to watch for
These are rarer, and they are the ones clinicians monitor for. Seek medical care if you have symptoms.
| Reaction | Frequency |
|---|---|
| Priapism | An erection that will not resolve. Reported as single cases. In one, aspiration and injected phenylephrine both failed and the man needed surgery; another had not recovered erectile function four weeks later |
| Rhabdomyolysis | Muscle breakdown that can injure the kidneys. One case after 6 mg injected at once. Creatine kinase reached 17,773 IU/L twelve hours in, kidney function fell, and the man spent three days in intensive care |
| Renal infarction | Blood supply to part of a kidney cut off. One case report, with a review of the literature beside it. The authors weigh a clotting effect and a direct toxic effect and settle on neither |
| New and darkening moles | The most frequently reported effect in this literature. A review of 179 patients with suddenly appearing moles put drugs including melanotan among the suspected causes in 41% of them, and 16% of all cases had at least one dysplastic mole confirmed under a microscope |
| Melanoma reported after use | Four case reports as of the 2017 review, describing melanomas arising in existing moles during or shortly after use. The review’s own verdict is that conclusive evidence linking the two is lacking |
When to seek medical care
Each one below is a serious reaction from the table above, written as the signs you would actually notice. Spotting them is the job of this section; working out what they mean is a clinician’s.
Acute kidney injury from dehydration
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When these effects tend to occur
The cited evidence describes these effects in relation to the dose and to the early period of taking it, rather than as a constant background throughout.
When a study reports how side effects changed over time, it describes the group as a whole. It cannot predict one person’s experience.
Common questions
How long do melanotan ii side effects last, and do they go away?
The sources do not commit to a set number of days. What they describe is a pattern — reactions cluster after you start and after each increase, then ease while the dose is held steady. Any page quoting an exact number of days is quoting something the sources do not say.
What are the most common melanotan ii side effects?
Nausea, drowsiness and tiredness and spontaneous erections — the table above has the rest, each with its frequency band and source.
Does melanotan ii have a boxed warning?
No, because a boxed warning is part of an FDA-approved label and melanotan ii has no approved label. That reflects what regulatory review has and has not covered, not a finding that serious risks were looked for and ruled out.
Can the melanotan ii dose be lowered if side effects are hard to tolerate?
That decision belongs to the prescribing clinician. No approved schedule exists for this compound, so there is no labeled framework for adjusting a dose. That leaves the prescriber as the only place the decision can sit.
Does melanotan ii cause hair loss?
Hair loss is not among the reactions listed on this page for melanotan ii, because the cited trial report cited here does not carry it. Anything missing from the tables is outside what can be sourced here rather than ruled out, and a symptom that worries you belongs with a clinician.
Is fatigue a listed melanotan ii side effect?
Yes — it is in the common reactions table above, with its frequency band. Being listed means it came up often enough in the trial population to reach the cited trial report; it does not establish the cause in any one case.
Is constipation a listed melanotan ii side effect?
Not separately. If a source groups stomach and gut events together, this page keeps that group intact. It does not invent named reactions the source never listed.
What should someone do about a serious melanotan ii reaction?
Contact a clinician promptly, and emergency services if symptoms are severe or getting worse quickly. The section above describes what those reactions actually look like, so they can be spotted early rather than explained away.
Do the frequencies on this page mean the chance it happens to one person?
No. These figures describe groups in a study. A band shows how often a reaction appeared under that trial’s conditions. It cannot predict what will happen to one person.
Related
The schedule these reactions were recorded against, the comparisons, and the sourcing rules behind every grade on this page.
What Melanotan II is, how it is used, and what has been studied
Melanotan II concentration and dose-draw tool
Check the same draw on a vial that is not Melanotan II
Fatigue weighed class-wide, including Melanotan II
Nausea weighed class-wide, including Melanotan II
The proceedings behind the Melanotan II note on this page
Every compound guide, Melanotan II and the rest
What a source must satisfy to appear on Melanotan II
- Dorr RT, Lines R, Levine N, Brooks C, Xiang L. Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical study. Life Sci. 1996;58(20):1777-84retrieved 2026-08-13limited human data
- Mallory CW, Lopategui DM, Cordon BH. Melanotan Tanning Injection: A Rare Cause of Priapism. Sex Med. 2021;9(1):100298retrieved 2026-08-13limited human data
- Nelson ME, Bryant SM, Aks SE. Melanotan II injection resulting in systemic toxicity and rhabdomyolysis. Clin Toxicol (Phila). 2012;50(10):1169-73retrieved 2026-08-13limited human data
- Peters B, Hadimeri H, Wahlberg R, Afghahi H. Melanotan II: a possible cause of renal infarction: review of the literature and case report. CEN Case Rep. 2020;9(3):219-222retrieved 2026-08-13limited human data
- Burian EA, Jemec GBE. Eruptive Melanocytic Nevi: A Review. Am J Clin Dermatol. 2019;20(5):669-682retrieved 2026-08-13limited human data
- Habbema L, Halk AB, Neumann M, Bergman W. Risks of unregulated use of alpha-melanocyte-stimulating hormone analogues: a review. Int J Dermatol. 2017;56(6):575-580retrieved 2026-08-13limited human data