Based on NIH | Does metformin taken at night interfere with sex or cause erectile dysfunction?

Metformin taken at night does not typically interfere with sexual activity and is not known to directly cause erectile dysfunction (ED). Most official drug information lists common side effects like stomach upset and low vitamin B12 over time, but sexual side effects are not established as a direct adverse effect of metformin itself. ^{[1] [2]} In fact, metformin improves insulin sensitivity and vascular health, which can indirectly support erectile function in people with insulin resistance or diabetes. ^{[3] [4]}

What official drug information says

• Metformin’s most common side effects include diarrhea, nausea, stomach discomfort, gas, indigestion, and changes in taste. Sexual dysfunction is not listed as a typical adverse effect. ^[1]
• The clinical safety summaries also emphasize issues like gastrointestinal symptoms and vitamin B12 reduction, rather than sexual side effects. ^[2]
• Metformin works by lowering glucose production in the liver and improving the body’s response to insulin, which helps overall metabolic and vascular health. Better vascular health can be helpful for erections. ^{[3] [4]}

Diabetes, nerves, and blood vessels

• Erectile dysfunction is common in people with diabetes due to nerve and blood vessel damage over time. Good glucose control is protective for sexual function. ^[5]
• While certain medications (for example, some blood pressure or antidepressant drugs) can contribute to ED, metformin is not typically one of them. Reviewing all medications with a clinician is a good step if ED occurs. ^{[6] [7]}

Evidence on metformin and erectile function

• In men with insulin resistance and poor response to sildenafil, adding metformin improved erectile scores over 2–4 months, while placebo did not; side effects were mainly mild gastrointestinal issues. This suggests metformin may enhance erectile function when insulin resistance is part of the problem. ^[8]
• Animal and mechanistic studies show metformin can improve penile vascular relaxation by enhancing nitric oxide pathways and adenosine signaling, and reversing hypertension-related changes in erectile tissue. These effects point toward a potential beneficial, not harmful, role in erection physiology. ^{[9] [10]}
• Systematic reviews of antidiabetic therapies suggest an overall protective role on erectile function across drug classes, including metformin, although more human studies are needed. ^[11]

Night dosing and timing around sex

• Metformin can be taken with meals to reduce stomach upset; extended‑release forms are often taken once daily. There is no guidance that night dosing specifically reduces sexual performance. If nighttime dosing causes stomach discomfort, moving the dose to dinner or earlier with food may help. ^[1]
• Because metformin does not cause sedation or acute vascular changes that impair erections, timing relative to sexual activity generally does not matter. Focus on consistent daily dosing and good glucose control. ^{[3] [4]}

When to look for other causes

• If erectile problems occur, it is reasonable to consider: diabetes control, blood pressure, cholesterol, smoking, alcohol, stress/anxiety, low testosterone, and other medications known to affect sexual function. Addressing these can make a big difference. ^{[6] [7]}
• If symptoms persist, a clinician can evaluate hormones, cardiovascular risk, and medication list, and may suggest targeted ED treatments.

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Key takeaways

• Metformin, including when taken at night, is not known to directly cause ED. ^{[1] [2]}
• Better insulin sensitivity and vascular function from metformin may support erectile health, particularly in insulin resistance. ^{[8] [9]}
• Manage diabetes well and review other potential contributors to ED; metformin timing is unlikely to be the issue. ^{[5] [6] [7]}

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