Can I Take Glycine With Vyleesi (Bremelanotide)?

What Is Vyleesi and Who Is It Approved For?

Vyleesi is the brand name for bremelanotide, a cyclic heptapeptide that activates melanocortin receptors, primarily MC1R and MC4R, in the central nervous system. The FDA approved bremelanotide in June 2019 specifically for hypoactive sexual desire disorder (HSDD) in premenopausal women. It is not approved for postmenopausal women, for men, or for any other sexual dysfunction category.

How bremelanotide actually works

HSDD is a real, diagnosable condition. Roughly one in ten premenopausal women meets diagnostic criteria, making it the most common female sexual dysfunction. Bremelanotide does not act on estrogen or progesterone receptors. Instead, it modulates dopaminergic and noradrenergic signaling through the melanocortin system, shifting the neurochemical balance in the brain's desire circuitry.

The drug is a subcutaneous auto-injector you use in the abdomen or thigh. Peak plasma concentration arrives roughly 60 minutes post-injection. Its half-life is approximately 2.7 hours. Because it clears fairly quickly, most pharmacokinetic interactions are time-limited.

The menstrual cycle and HSDD

Sexual desire in women is not static across the cycle. Testosterone and estrogen peak around ovulation, which often correlates with higher spontaneous desire. In the luteal phase, progesterone rises and desire may dip. Women with HSDD often report that this luteal trough is when symptoms feel worst. Bremelanotide is taken on an as-needed basis, so you can time use for the days when desire is lowest, rather than taking it daily.

What Is Glycine and Why Do Women Take It?

Glycine is the simplest amino acid. Your body makes it, and you get small amounts from meat, fish, and legumes, but supplemental doses (typically 3-5 g at bedtime) are commonly used for sleep quality, glycemic support, and as a building block for collagen synthesis.

Sleep benefits

A randomized crossover trial published in Sleep and Biological Rhythms found that 3 g of glycine taken before bed improved subjective sleep quality and reduced daytime sleepiness in adults who had restricted sleep. The mechanism appears to involve glycine's role as an inhibitory neurotransmitter in the spinal cord and brainstem, lowering core body temperature to support sleep onset.

Glycemic and metabolic relevance for women

Women with PCOS and insulin resistance sometimes add glycine to support glycemic control. A small trial found that glycine supplementation at 5 g/day for 3 months reduced fasting glucose and improved insulin sensitivity in metabolic syndrome patients. The evidence is preliminary, but given that PCOS affects up to 10-13% of reproductive-age women and is a common backdrop for hormonal and sexual health concerns, this overlap is worth naming.

Collagen synthesis

Glycine is the primary amino acid in collagen, making up roughly one-third of collagen's structure. Women post-partum or in early perimenopause often add glycine because collagen turnover accelerates with declining estrogen. This is a distinct use case from the sedation or glycemic applications, and it carries no special concern in the context of bremelanotide.

Is There a Pharmacokinetic Interaction Between Glycine and Bremelanotide?

No clinically significant pharmacokinetic interaction has been identified. Bremelanotide is metabolized primarily through proteolysis, not through cytochrome P450 enzymes. The prescribing information for Vyleesi lists no CYP-based drug interaction warnings for the drug itself.

Glycine is handled by amino acid transporters and glycine cleavage system enzymes in the liver and kidney. It does not meaningfully inhibit or induce CYP3A4, CYP2D6, or other major metabolic enzymes. Because the two agents travel on entirely separate metabolic roads, their plasma concentrations are unlikely to affect each other.

What the research does not tell us is whether high-dose glycine (above 10 g/day) could theoretically compete with other amino acids for transport in ways that affect peptide absorption. No human pharmacokinetic study has examined glycine alongside bremelanotide. Women deserve to know that absence of evidence is not the same as evidence of safety. This is an honest data gap.

What About Pharmacodynamic Interactions?

This is where the real clinical conversation sits. Bremelanotide carries two well-documented pharmacodynamic effects beyond its intended action on desire: transient blood pressure increases and nausea.

Blood pressure

The Vyleesi prescribing label warns that bremelanotide transiently raises systolic blood pressure by an average of 6 mmHg and diastolic by 3 mmHg, peaking around 4 hours post-injection before returning to baseline within 12 hours. Women with uncontrolled hypertension or cardiovascular disease are advised against using the drug.

Glycine, by contrast, has mild vasodilatory properties. Glycine receptors on vascular smooth muscle cells are activated by the amino acid, leading to modest relaxation. A brief counter-effect on bremelanotide's blood pressure rise is biologically plausible but has not been tested in a controlled trial.

The more meaningful concern runs in the other direction. If you take glycine for sleep at bedtime and then take bremelanotide the following morning or early in the day, there is no significant overlap. The risk window tightens only if you take glycine close to the time of Vyleesi use.

Sedation

Glycine's inhibitory neurotransmitter role means high doses can cause sedation, particularly at bedtime doses of 3-5 g. Bremelanotide's prescribing data lists fatigue as an adverse event occurring in approximately 2% of trial participants. Stacking a sedating supplement on top of a drug that causes some fatigue, even mildly, is worth timing carefully. Taking glycine in the morning alongside your Vyleesi dose is not a combination most women would choose for lifestyle reasons, but if it happens, increased drowsiness is the main thing to watch for.

Nausea

Nausea was the most common adverse event in the RECONNECT trials, occurring in roughly 40% of women using bremelanotide. Glycine does not have a known pro-emetic effect. Some research suggests glycine may actually have gastroprotective properties. No interaction on this axis is expected.

A Practical Timing Framework for Women Taking Both

The simplest way to manage glycine and Vyleesi together is to keep them in separate daily windows. Here is a concrete approach:

Bedtime glycine routine:

• Take 3-5 g glycine in water 30 minutes before sleep.
• This is your sleep, collagen, or glycemic-support dose.
• Bremelanotide is cleared to roughly 15% of peak plasma levels within 8-10 hours of dosing, so morning or afternoon Vyleesi use creates no meaningful overlap with the prior night's glycine dose.

Vyleesi timing:

• Inject bremelanotide at least 45 minutes before anticipated sexual activity, per FDA labeling.
• Do not inject within 8 hours of bedtime if you have taken or plan to take glycine that same evening. This avoids additive sedation and keeps the blood pressure profiles from coinciding.
• Use no more than one Vyleesi dose in 24 hours, and no more than one dose per anticipated sexual encounter.

If you already took both close together:

• Lie down if you feel dizzy.
• Check your blood pressure if you have a home cuff.
• Drink water. Bremelanotide's transient pressor effect usually resolves within 12 hours, and glycine's mild vasodilation may actually soften it slightly.
• Call your prescriber if systolic BP exceeds 160 mmHg or if dizziness is severe.

Who This Combination Is Right For (and Who Should Be Cautious)

Reproductive-age women with HSDD and sleep concerns

If you are a premenopausal woman using Vyleesi for HSDD and you want glycine for sleep quality, the combination is reasonable with proper timing. Both agents serve different goals, different windows, and different mechanisms.

Women with PCOS

PCOS is worth a specific mention. Women with PCOS have higher rates of androgen excess, insulin resistance, and disrupted sleep. Glycine's glycemic and sleep benefits are particularly relevant in this population. HSDD is also more prevalent in women with PCOS, partly because of androgen imbalance and partly because of the psychological burden of the condition. The combination of glycine at bedtime for metabolic support and Vyleesi on an as-needed basis for desire is a clinically coherent strategy, as long as cardiovascular status is normal.

Women with hypertension or cardiovascular disease

Bremelanotide is not recommended for women with uncontrolled hypertension or known cardiovascular disease. If you are in this group, adding glycine does not resolve the Vyleesi contraindication. The conversation with your cardiologist or OB-GYN should happen before any HSDD medication is started.

Women in perimenopause or post-menopause

Vyleesi is approved only for premenopausal women. If you are in perimenopause or post-menopause and are experiencing low sexual desire, your clinician's first step should be ruling out genitourinary syndrome of menopause (GSM), checking estrogen and testosterone levels (free and total), and considering whether menopausal hormone therapy addresses the root cause. Glycine for sleep is commonly used in this life stage, but Vyleesi is not an on-label option.

Pregnancy, Lactation, and Contraception

This section is required and applies to every woman considering Vyleesi.

Pregnancy

Bremelanotide is contraindicated in pregnancy. Animal studies at doses roughly equivalent to 16 times the human subcutaneous dose showed fetal harm, including reduced fetal weight and delayed ossification. There are no adequate human data on bremelanotide use during pregnancy. If you are pregnant or become pregnant while using Vyleesi, stop the medication immediately and contact your OB-GYN.

Because HSDD is a diagnosis for premenopausal women of reproductive age, most users are in the fertility window. Reliable contraception is required while using bremelanotide. Your prescriber should discuss your current contraceptive method at the time of prescription. Hormonal contraception does not appear to alter bremelanotide's pharmacokinetics, but no dedicated interaction study exists.

If you are trying to conceive, Vyleesi should be discontinued before stopping contraception. Bremelanotide is cleared within approximately 24 hours of each dose, so washout is rapid.

Lactation

The FDA label states that bremelanotide has not been studied in breastfeeding women. No human milk transfer data exist. Because of the potential for harm and because low sexual desire in the postpartum period is often driven by low estrogen and elevated prolactin rather than by the central pathways bremelanotide targets, The Menopause Society and most women's health clinicians would advise against using Vyleesi during lactation. A referral for postpartum sexual health counseling and hormone evaluation is a more appropriate first step.

If you are trying to conceive and using glycine

Glycine has a strong safety record in pregnancy and is considered a conditionally essential amino acid during gestation because fetal demand may exceed maternal synthesis capacity. If you are discontinuing Vyleesi to try to conceive, continuing glycine for sleep or metabolic support poses no known fetal risk. This is one case where glycine's safety profile clearly diverges from bremelanotide's.

What the Evidence Gaps Mean for You

Women have been historically underrepresented in pharmacology trials, and HSDD research is no exception. The two key RECONNECT trials (RECONNECT 1 and 2) enrolled exclusively premenopausal women, which is appropriate for the indication but means the data set on bremelanotide is relatively small compared to most approved drugs.

No published trial has examined glycine co-administration with any melanocortin receptor agonist. The interaction data discussed in this article is reasoned from mechanism, not from a head-to-head trial. Glycine is generally regarded as safe at doses up to 15-24 g/day based on toxicology data, but the absence of direct co-administration data is a real gap.

Women using both agents should tell their prescribing clinician. This is not because the risk is established, but because documentation matters. If an unexpected blood pressure event or unusual fatigue occurs, your prescriber needs the full supplement picture.

Monitoring and Practical Checkpoints

If you are using Vyleesi and glycine together, here is a reasonable monitoring approach:

• Blood pressure: Check BP at home on a day when you take both, approximately 4-6 hours after Vyleesi injection. A reading above 140/90 mmHg warrants a call to your provider.
• Sedation: Rate your daytime alertness on a 1-10 scale for the first two or three cycles of co-use. If daytime sleepiness worsens, consider dropping the glycine dose from 5 g to 3 g.
• Nausea: Primarily a Vyleesi effect. Eating a light meal before injection may reduce it. Glycine is not expected to worsen nausea.
• Libido response: Track your desired-sex desire score across cycles using a validated tool such as the Female Sexual Function Index (FSFI). If glycine is improving sleep quality, you may see secondary improvement in desire scores independent of bremelanotide, since sleep deprivation is a well-established suppressor of female sexual desire.

Other Supplements and Vyleesi: Brief Notes

Glycine is not the only supplement that comes up alongside Vyleesi questions. A few others worth naming briefly:

• Magnesium glycinate: Contains glycine. The same timing principles apply. Magnesium itself has mild blood pressure lowering effects, adding one more reason to separate evening supplementation from Vyleesi dosing.
• Maca (Lepidium meyenii): Sometimes marketed for libido in women. Evidence is weak and inconsistent. No known pharmacokinetic interaction with bremelanotide, but no meaningful added benefit has been shown when combined with an approved medication.
• Ashwagandha: An adaptogen sometimes used for stress and low libido in women. One trial found ashwagandha root extract (300 mg twice daily for 8 weeks) improved FSFI scores in women with sexual dysfunction. No interaction data with bremelanotide exist.
• CBD: Has mild CYP3A4 inhibitory properties at high doses. Bremelanotide is not a CYP3A4 substrate, so a direct pharmacokinetic interaction is not expected, but the combination has not been studied.

Always give your prescriber a full supplement list before starting Vyleesi.