Can you take metformin with Viagra? Yes — neither medicine's Australian label lists the other as an interaction. Metformin is not on the Viagra leaflet's list, and sildenafil, the medicine in Viagra, is not on the metformin leaflet's. Diabetes itself matters more: it is a common cause of erection problems, and it raises eye and heart questions the doctor who prescribes sildenafil will want to check. The one thing never allowed with Viagra is nitrates, the medicines for angina.

Does metformin interact with Viagra?

No interaction is listed. The Australian consumer medicine information for metformin (sold as Diabex, among other names) lists the medicines that may interact with it — other blood-glucose medicines, some blood-pressure and heart medicines, warfarin, anti-inflammatory painkillers, cimetidine, steroids and more — and no erectile dysfunction medicine is among them (Diabex CMI). Metformin does not appear in the Viagra leaflet (Viagra CMI) or in the Australian and European sildenafil labels. The one blood-glucose tablet the sildenafil label did test, tolbutamide, showed "no significant interactions" (EMA — Viagra). "Not listed" is not the same as "tested and safe", so tell the prescriber you take metformin. For tadalafil (Cialis), no specific studies with antidiabetic medicines were done (EMA — Cialis); its full list is in what interacts with Cialis?

Can metformin cause erectile dysfunction?

It is not a listed side effect. The metformin leaflet's side effects are mostly stomach upsets — nausea, diarrhoea, stomach pain, a changed sense of taste — plus lactic acidosis, a rare but serious build-up of acid in the blood; erection problems are not on the list (Diabex CMI). The condition is the likelier link. Healthy Male puts the chance of erectile dysfunction at more than twice as high in diabetic men as in other men (Healthy Male), and healthdirect lists it among the problems that erectile dysfunction can be the first sign of, alongside heart disease and high blood pressure. Some medicines for blood pressure and cholesterol can also affect erections (healthdirect — Erectile dysfunction). More: erectile dysfunction in men with diabetes.

Does Viagra work in men with diabetes?

Yes, though for a smaller share of men than in most other groups. In a 12-week trial of 268 diabetic men, 56% on sildenafil reported improved erections against 10% on placebo, and 61% had at least one successful attempt at intercourse against 22% (Rendell et al., 1999). Across all the Viagra trials, 59% of diabetic patients reported improvement, against 16% on placebo (Viagra PI (Australia)), compared with 68% of men whose erection problems had any physical cause (EMA — Viagra). Some diabetic men need the top 100 mg dose, where side effects may be more common (Viagra PI (Australia)). Tadalafil works too, and no dose change is needed for diabetic men (Cialis PI (Australia)). The options compared: ED medicines for diabetic patients and treatment options for ED with diabetes.

What should diabetic men check before taking Viagra?

  • Eyes. The Viagra leaflet asks diabetic men to check with their doctor first, especially if they also have eye problems (Viagra CMI). The Australian label has limited safety data in diabetic retinopathy and advises Viagra in untreated retinopathy only "after careful benefit-risk assessment" (Viagra PI (Australia)). Stop and seek help urgently if your vision suddenly changes (Viagra CMI).
  • Heart. Sex can strain the heart, so the doctor checks you are fit for it, and Viagra is never taken with nitrates (Viagra CMI): nitroglycerin and Viagra.
  • Dizziness. It is a side effect of Viagra (Viagra CMI) and an early sign of low blood glucose, which metformin alone does not normally cause but can when taken with sulfonylureas or insulin (Diabex CMI).
  • Alcohol. Heavy drinking on metformin "may also lead to serious side effects" (Diabex CMI), and alcohol can temporarily weaken erections (Viagra CMI): can you drink alcohol with Viagra?

Can metformin help erections?

It is not a treatment for them. One pilot trial gave metformin or placebo to 30 non-diabetic men with insulin resistance and a poor response to sildenafil: erection scores rose on metformin over four months, and side effects, mostly stomach upsets, were more common (61.5% against 7.7%) (Rey-Valzacchi et al., 2012). Metformin is prescribed to control blood glucose (Diabex CMI). For erections, healthdirect's options beyond the tablets include injections, vacuum devices, counselling and lifestyle changes (healthdirect — ED medicines).

The short answer

Metformin and Viagra are not listed as interacting, and sildenafil works for many diabetic men. Tell the prescriber you take metformin, have your eyes and heart checked, go easy on alcohol, and never combine Viagra with nitrates. Metformin itself is on our Glucophage page and in our guide "Type 2 Diabetes Medicines in Australia". The Glucophage brand name returns no result on the Australian register (ARTG: Glucophage), while metformin is registered as Diabex and under many other names (ARTG: metformin). Every other combination: can Viagra be taken with other medicines? and our guide to taking Viagra or Cialis with other medicines; metformin's own place in treatment: type 2 diabetes medicines, metformin to semaglutide.