PT-141 side effects

Side effects by frequency

The figures below come from the two 24-week phase 3 trials summarized in the Vyleesi label. They compared bremelanotide 1.75 mg, used as needed, with placebo in premenopausal women.¹

Very common: more than 1 in 10 users

Nausea is covered in its own section below. No flushing events were serious, and fewer than 1% were severe.¹ Injection site reactions included pain, redness, bruising, bleeding, itching, tingling and numbness at the site.¹

Common: 2% to 10% of users

These rates also come from the label's adverse reaction table.¹

Less common: under 2% of users

Less common reactions, each in under 2% of users and more often than with placebo, included upper abdominal pain, diarrhea, muscle pain and joint pain.¹ The label also lists restless legs syndrome, runny nose, raised creatine phosphokinase, raised blood pressure and pain in a limb.¹

How nausea runs its course

The label reports a median onset within one hour of a dose and a duration of about two hours.¹ The published trial report gives a median onset of 30 minutes and a median duration of 2.4 hours, with about 98% of cases mild to moderate.² Nausea was most frequent after the first dose, at 21% of patients, and fell to about 3% after later doses.¹ In the trials, 13% of women on the drug needed anti-nausea medicine.¹ The patient information says it usually goes away by itself, though it can last longer in some people.¹ For persistent or severe nausea, the label advises considering stopping, or anti-nausea medicine for patients who want to continue.¹

Blood pressure and heart rate

After each dose, systolic blood pressure rose by up to 6 mmHg and diastolic by up to 3 mmHg, while heart rate fell by up to 5 beats per minute.¹ Both usually returned to baseline within 12 hours.¹ In a 397-woman trial using ambulatory (wearable) blood pressure monitoring, the 1.75 mg dose raised systolic pressure about 3 mmHg more than placebo in the 4 hours after a dose, with peaks that usually lasted less than 15 minutes.⁴ A 2022 review of the whole development program found small, short-lived but statistically significant rises and advised caution in anyone at risk of cardiovascular disease.⁵ The label contraindicates bremelanotide in uncontrolled high blood pressure or known cardiovascular disease.¹

Skin darkening

Bremelanotide can cause focal hyperpigmentation: darker patches on the face, gums or breasts.¹ It appeared in 1% of women using up to 8 doses a month, with no cases on placebo, and in 38% of people given a dose daily for 8 days.¹ Across the development program it developed in more than one third of people given up to 16 daily doses in a row.⁵ People with dark skin were more likely to be affected, and the patches did not always fade after stopping.¹ The label links this to MC1 receptors on pigment cells, whose activation raises melanin.¹

Stopping treatment and serious events

In the phase 3 trials, 18% of women on bremelanotide stopped because of side effects, versus 2% on placebo.¹ Nausea was the leading reason, at 8%.¹ Serious adverse reactions occurred in 1.1% of women on the drug versus 0.5% on placebo.¹ One case of acute hepatitis was reported in the open-label extension, in a woman who had used 10 doses over a year.¹ Her liver tests returned to normal 4 months after stopping.¹ The drug could not be ruled out as the cause, and the program showed no wider liver signal.¹ A 2022 pooled review of 43 studies with about 3,500 people found no deaths.⁵ In the 52-week open-label extension of 684 women, the most common side effects judged related to the drug were nausea (40.4%), flushing (20.6%) and headache (12.0%), with no new safety signals.⁶

Warnings and interactions

• Other medicines: bremelanotide may slow stomach emptying and reduce absorption of drugs taken by mouth. The label says to avoid it with oral naltrexone products.¹
• Pregnancy: animal studies suggest possible harm to a fetus, so the label advises effective contraception and stopping if pregnancy is suspected.¹
• Breastfeeding: FDA required a trial measuring bremelanotide in breast milk and approved a label update based on it on October 23, 2026.⁷⁸⁹ Check the current label before relying on older breastfeeding statements.
• Heart rhythm and cancer studies: a 20 mg nasal dose did not prolong the QTc interval to a clinically relevant extent.¹ Two-year animal studies found no significant rise in tumors.¹

Side effects in men and in research vials

In small studies of men, mostly with a nasal form, flushing and nausea were the most common side effects.¹⁰ A 19-man study that combined nasal PT-141 with sildenafil reported no new adverse events.¹¹ A 2026 review of peptides in sexual medicine raises concerns about product quality, dosing variability and incompletely characterized adverse effects for melanotan II and related peptides sold through unregulated markets.¹² Research-labeled PT-141 vials have no approved application, so FDA has not reviewed their content or quality, and no reviewed source characterizes their side effects.¹³

Related pages: What is PT-141?, PT-141 dosage and PT-141 benefits and uses.