Melanotan 1: why the tan comes out patchy

A user on r/peptides recently lost 50 pounds with tirzepatide, noticed loose and crepey skin on their arms and knees, and decided to try Melanotan 1 to stay evenly tanned. The result, in their words: "I am now tiger-striped." ^[1] The pattern is not random. It follows directly from how Melanotan 1 works and what rapid weight loss does to skin.

The key finding: the hormone does not know which skin faces the sun

Afamelanotide, the pharmaceutical form of Melanotan 1, is a synthetic analogue of alpha-melanocyte-stimulating hormone (alpha-MSH). It binds to MC1R receptors on melanocytes and triggers eumelanin production. The critical detail: it does this independent of prior UV light exposure. ^[2] Natural tanning requires UV photons to activate the process. Melanotan 1 bypasses that gate. Every melanocyte the hormone reaches, whether in sun-exposed skin or deep in a skin fold, gets the same signal.

In young, elasticated skin, this distinction rarely shows. The skin sits flat. Exposed and unexposed surfaces are nearly the same surface. The tan looks even.

In older or lax skin, it matters enormously. Wrinkles, creases, and folds create entire planes of skin that receive no sunlight under normal conditions. A clinical review in Journal of Drugs in Dermatology notes that "diffuse hyperpigmentation is experienced by almost all patients" on afamelanotide, ^[3] without distinguishing exposed from unexposed surfaces, because the mechanism does not make that distinction.

Why GLP-1 weight loss amplifies the effect

The tirzepatide context in the Reddit post is not incidental. Research published in Dermatology Surgery in 2026 found that GLP-1 receptor agonist use produces "loss of elasticity and skin sagging/laxity" through reduced collagen production and degradation of elastic fibres. ^[4] A companion paper in the same journal described GLP-1-associated weight loss causing "increased skin laxity" alongside subcutaneous tissue changes that go beyond simple volume loss. ^[5]

The practical result is that someone who has lost significant weight via tirzepatide or semaglutide may have substantially more hidden skin surface than they did before the weight loss, or than a same-age person who lost weight more slowly. Loose skin on the arms bunches. The inside of elbow creases, the underside of the upper arm, the skin behind the knee -- these surfaces fold inward and rarely see direct light. For someone in their 60s, this effect compounds with age-related loss of skin elasticity that was already present before any weight loss.

Apply Melanotan 1. The hormone reaches all of it. The sun does not. The result is a high-contrast stripe pattern wherever sunlit skin meets the shaded interior of a fold.

What this is not

This is not a rare adverse reaction. The mechanism is predictable from first principles, not a pharmacological surprise. The hormone works as designed. The interaction with loose, aged, or post-weight-loss skin is a geometry problem, not a toxicity problem.

It is also not a dosing error. Using less Melanotan 1 reduces the overall depth of pigmentation but does not change which skin surfaces respond. A smaller dose produces a lighter version of the same pattern, not an even one. The only way to avoid the contrast lines is to avoid the compound, or to ensure that the skin areas receiving the hormone are all in roughly equivalent sun exposure, which is not realistic in practice.

It is also not a reason to conclude Melanotan 1 is dangerous in this context. The pigmentation change is cosmetic and reversible as the compound clears. The safety profile of afamelanotide in clinical use is well-characterised: common adverse events in FDA-reviewed trials include implantation site reactions (21%), nausea (19%), throat pain (7%), fatigue (6%), and dizziness (4%); no serious hepatic adverse events were recorded. ^[6]

The issue is that uneven tanning can itself be distressing, and users combining Melanotan 1 with a recent history of GLP-1 weight loss should expect it. The FDA-approved version (Scenesse) is authorised only for prevention of phototoxicity in adults with erythropoietic protoporphyria. ^[6] Cosmetic tanning applications sit outside that indication in every covered jurisdiction.

Practical context

Melanotan 1 amplifies every melanocyte it reaches. In skin that lies flat, that produces an even tan. In skin with significant laxity -- whether from age, weight history, or post-GLP-1 weight loss -- it maps the geography of the folds. The more pronounced the loose skin, the sharper the contrast lines.

If you are considering Melanotan 1 after significant weight loss, the available evidence suggests the tan will not be uniform, and the degree of unevenness will track closely with how much loose skin is present. That is not a framing issue or a dosing issue. It is a mechanism issue, and no dose adjustment resolves it.

What we do not yet know: whether skin retraction over time (as the body readjusts after weight loss) meaningfully changes this outcome, and whether topical-only application methods would produce a different pattern from systemic dosing. The published literature on Melanotan 1 focuses on erythropoietic protoporphyria, where uneven pigmentation is a documented but secondary concern relative to phototoxicity reduction. No controlled data compares outcomes in young versus older or post-weight-loss skin.

For context on how the melanocortin system works more broadly, see the overview of PT-141 (bremelanotide), another melanocortin receptor agonist with a different clinical application and a separate regulatory history.