PT-141 Side Effects Reported in Clinical Trials.

Most commonly reported side effects

PT-141 side effects from the bremelanotide Phase 3 double-blind data set, comparing the 1.75 mg subcutaneous arm with placebo, were dominated by gastrointestinal and vasomotor adverse events. The integrated safety review across the development program (3,500+ subjects, 43 studies) reported the following Phase 3 frequencies in the active arm versus placebo ^[3][5]:

• Nausea: 40.0% vs 1.3% placebo — the leading adverse event and the leading reason for discontinuation
• Flushing: 20.3% vs 1.3%
• Headache: 11.3% vs 1.9%
• Injection-site reactions: 5.4% vs 0.5%

Most events were mild to moderate in severity. Approximately 18% of subjects in the bremelanotide arm discontinued treatment due to adverse events in the pivotal program, with nausea the dominant cause ^[5].

Transient blood pressure elevation

Twenty-four-hour ambulatory blood pressure monitoring after eight consecutive days of daily 1.75 mg subcutaneous dosing showed a mean increase of approximately 1.9 mmHg systolic and 1.7 mmHg diastolic, with a transient peak systolic increase of approximately +2.8 mmHg at 4-8 hours post-dose; blood pressure returned to baseline by 8-10 hours after each dose ^[4][19]. A premenopausal-women substudy confirmed the same time course: transient rise peaking 2-4 hours after dosing, return to baseline within 8-10 hours, with no sustained 24-hour blood pressure elevation ^[19].

Vyleesi label. The product is contraindicated in uncontrolled hypertension and in known cardiovascular disease. The per-occasion (rather than chronic) dosing model is partly informed by the blood-pressure time course.

The time-course evidence is what supports the per-occasion dosing model: the BP signal resolves within hours, the dose is taken at most once per 24 hours and eight times per month, and chronic continuous exposure is not part of the approved use.

Focal hyperpigmentation

Focal hyperpigmentation — discrete pigmented patches on the face, gingiva, and breasts — was reported in approximately 1% of subjects receiving Vyleesi up to the label maximum of eight doses per month in trials ^[4][5]. The frequency rose sharply to approximately 38% in a substudy that gave subjects daily 1.75 mg subcutaneous dosing for eight consecutive days, demonstrating a clear dose-frequency dependence ^[4]. Risk was higher in subjects with darker baseline skin pigmentation. Resolution after discontinuation was not confirmed in all cases ^[4].

The mechanism is MC1R cross-activity: PT-141 is a non-selective melanocortin agonist, and although MC4R agonism is the therapeutic action, residual MC1R agonism on cutaneous melanocytes drives the pigmentary change ^[1][4]. The frequency cap on the approved label (no more than eight doses per month) reflects this dose-frequency-dependent risk.

Pigmentation differences from Melanotan II

Does PT-141 make you tan? PT-141 has lower MC1R affinity than its parent compound Melanotan II — the C-terminal amide deletion shifts selectivity toward MC4R-driven central effects — so generalized tanning is uncommon at label-defined dosing frequency ^[1]. The documented finding in the bremelanotide trial record is focal hyperpigmentation (discrete patches on the face, gingiva, breasts), not systemic tanning ^[4][5].

Hepatic and metabolic safety

Bremelanotide is metabolized by hydrolysis of amide bonds via cellular peptidases. The NIDDK LiverTox monograph notes only mild, transient serum aminotransferase elevations have been associated with bremelanotide exposure and no clear pattern of clinically apparent hepatotoxicity has been established; routine liver function monitoring is not required by the approved label ^[15]. Drug-drug interactions are minimal due to the peptidase metabolism route, which does not engage cytochrome P450 pathways ^[15].

Serious cardiovascular events

The integrated safety review across the development program documented two serious cardiovascular events across more than 3,500 subjects, contributing to the label contraindication in uncontrolled hypertension or known cardiovascular disease ^[5][4].