PT-141 side effects: what the trials report

PT-141 (bremelanotide), sold in the United States as Vyleesi, is the only FDA-approved melanocortin receptor agonist. Because it went through two pivotal Phase 3 trials and carries an FDA prescribing information label, the adverse-event picture is far clearer here than for most peptides discussed on this site^[1]. This article pulls the numbers directly from that label and from the RECONNECT trial publications, and draws the line between what is common, what is rare, and what the contraindications actually say.

Common adverse events: what the trials reported

The RECONNECT programme (studies BMT-301 and BMT-302) enrolled 1,247 premenopausal women with hypoactive sexual desire disorder. Across both studies, three adverse events occurred in 10% or more of participants on bremelanotide^[2]: nausea, flushing, and headache. The prescribing information puts the specific rates at nausea 40%, flushing 20.3%, headache 11.3%, injection site reactions 13.2%, and vomiting 4.8%^[1]. Most were mild to moderate in intensity.

Nausea is the dominant signal. In the 52-week open-label extension study (Simon et al. 2019, n=684 continuing participants), nausea remained at 40.4%, flushing at 20.6%, and headache at 12.0%, which tells us the rates do not meaningfully attenuate with extended use on an on-demand schedule.

One in five participants on Vyleesi discontinued because of an adverse event overall (18%, versus 2% on placebo in the controlled phase). Nausea drove the largest share of those discontinuations at 8%^[1]. The label also notes that pre-treatment with oral ondansetron, given 30 minutes before the injection, does not reduce the incidence of bremelanotide-associated nausea and is not recommended.

The cardiovascular signal: blood pressure and heart rate

Every dose of bremelanotide produces a transient increase in blood pressure alongside a transient decrease in heart rate. The label reports maximum mean increases of 6 mmHg in systolic and 3 mmHg in diastolic blood pressure, peaking 2 to 4 hours after injection, with return to baseline typically within 12 hours^[1]. Heart rate falls by up to 5 beats per minute on the same timeline.

For most healthy premenopausal women, that transient shift is not clinically significant. For people with uncontrolled hypertension or known cardiovascular disease it could be. Those two conditions are the only formal contraindications in the label: Vyleesi should not be used in patients with either.

There is no boxed warning in the current Vyleesi prescribing information. The cardiovascular signal sits in the Warnings and Precautions section, not at the top of the label.

Focal hyperpigmentation: a dose-frequency-dependent effect

A less commonly discussed finding is focal hyperpigmentation. At the approved on-demand schedule (up to 8 doses per month), the label reports this in approximately 1% of patients, most often on the face, gums, or breasts, and more commonly in patients with darker baseline skin tone^[1]. Importantly, the label states that resolution of the focal hyperpigmentation was not confirmed in all patients after discontinuation.

The dose-frequency relationship is striking. A separate study using daily dosing for 8 consecutive days produced hyperpigmentation in 38% of participants. That is why the label caps on-demand use at no more than 8 doses per month, a threshold the pivotal trials were designed to stay within.

What the label does not cover: off-label populations

The entire adverse-event dataset from Vyleesi trials is in premenopausal women with HSDD. The prescribing information contains no safety data for postmenopausal women, men, or any other population. Those uses are off-label, meaning clinicians can prescribe in those contexts but there is no formal evidence base for safety rates. Researchers have recently called for bremelanotide trials in men with sexual dysfunction^[3], and a 2026 systematic review included bremelanotide in a broader survey of female sexual dysfunction treatment options^[4], but neither provides AE rates for populations outside the approved indication.

Grey-market 'PT-141' research vials sold online are not the same product as Vyleesi. They are unlicensed, their purity and dose accuracy are unverified, and the adverse-event profile of the approved product does not automatically transfer to them. For the regulatory picture by country, see the PT-141 regulation pages.

What we do not yet know

Two gaps stand out. First, long-term cardiovascular outcomes. The 52-week extension study (Simon 2019) reported on continued adverse events but was not powered or designed to detect hard cardiovascular endpoints. Second, hyperpigmentation reversibility. The label's statement that resolution was not confirmed in all patients after stopping Vyleesi is a signal without a resolution study behind it. If you are weighing this drug and have any history of hyperpigmentation concerns or cardiovascular risk factors, those are the two questions to bring to a prescribing clinician.