Tadalafil and Metformin: Can You Take Them Together?

Takes less than 2 minutes to complete 100% online

What is Tadalafil and What is Metformin?

Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor licensed in the UK to treat erectile dysfunction (ED). It works by relaxing blood vessels in the penis, allowing increased blood flow when you are sexually aroused. Tadalafil is available as an on-demand treatment (10 mg or 20 mg taken at least 30 minutes before sex, with effects lasting up to 36 hours) or as a daily low-dose tablet (2.5 mg or 5 mg) for continuous support [4]. It requires sexual stimulation to work and does not cause spontaneous erections.

Metformin is a widely prescribed medicine for type 2 diabetes. It helps lower blood sugar by reducing glucose production in the liver and improving the body's response to insulin. Metformin is often the first-line treatment for type 2 diabetes and is taken once or twice daily with meals. Because diabetes is a common cause of erectile dysfunction—affecting blood vessels and nerves—many men with diabetes also seek treatment for ED [1][2].

Can You Take Tadalafil and Metformin Together?

Yes, tadalafil and metformin can generally be taken together. There is no known direct pharmacological interaction between these two medicines, meaning they do not interfere with each other's mechanisms of action or metabolism in a clinically significant way [4][12]. Many men with type 2 diabetes who take metformin are successfully prescribed tadalafil or other PDE5 inhibitors for erectile dysfunction.

However, it is essential that your prescriber knows about all your current medicines, including metformin, during your consultation. Diabetes can increase the risk of cardiovascular disease, and erectile dysfunction itself can be an early warning sign of heart or blood vessel problems [1][2]. Your prescriber will assess your overall cardiovascular health, blood pressure, and any other medicines you take to ensure tadalafil is safe and appropriate for you. Never start or stop any prescribed medicine without professional advice.

When to get urgent help

• Erection lasting more than 4 hours (priapism)—go to A&E immediately
• Sudden loss of vision or hearing—stop tadalafil and seek urgent medical help
• Chest pain during or after sex—stop activity, call 999, and do not take more tadalafil
• Severe dizziness or fainting—sit or lie down and contact your GP or NHS 111 the same day

Call 999 or go to A&E in an emergency, or contact NHS 111 for urgent advice.

What Your Prescriber Checks Before Prescribing Tadalafil and Metformin

When you request tadalafil and you are already taking metformin, your prescriber will carry out a thorough clinical assessment. They will ask about your diabetes control, any complications (such as nerve damage or kidney problems), your blood pressure, and your cardiovascular history. This is because men with diabetes are at higher risk of heart disease, and sexual activity itself places demands on the heart [2][4].

Your prescriber will also check for any other medicines you take that might interact with tadalafil. Critically, tadalafil must never be taken with nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, or recreational drugs known as 'poppers', as these combinations can cause a dangerous drop in blood pressure [4]. If you take blood pressure medicines or alpha-blockers (for prostate symptoms), your prescriber will ensure you start on the lowest suitable dose of tadalafil and that you are stable on your other treatments.

Why Diabetes Matters for ED Treatment

Diabetes can damage blood vessels and nerves over time, both of which are essential for achieving and maintaining an erection. High blood sugar levels can also reduce the effectiveness of ED treatments if diabetes is poorly controlled [1][2]. Your prescriber may discuss optimising your diabetes management alongside prescribing tadalafil, as better blood sugar control can improve erectile function. If you have not seen your GP recently about your diabetes, it is a good idea to arrange a review.

How Tadalafil and Metformin Work in Your Body

Tadalafil works by blocking an enzyme called phosphodiesterase type 5 (PDE5). This enzyme normally breaks down a substance called cyclic GMP, which relaxes smooth muscle in the blood vessels of the penis. By inhibiting PDE5, tadalafil allows cyclic GMP to accumulate, leading to improved blood flow and an erection when you are sexually stimulated [4]. Tadalafil does not directly affect blood sugar levels or insulin.

Metformin works primarily in the liver, where it reduces the amount of glucose released into the bloodstream. It also makes muscle cells more sensitive to insulin, helping your body use glucose more effectively. Metformin does not directly affect the blood vessels in the penis or the enzymes that tadalafil targets. Because the two medicines act on different systems in the body, they do not interfere with each other's effects [12].

That said, both diabetes and some of its complications can affect erectile function. Nerve damage (neuropathy) and blood vessel damage (vascular disease) caused by long-term high blood sugar can make it harder to achieve an erection, even with treatment. This is why your prescriber will consider your overall diabetes control and any complications when prescribing tadalafil.

Practical Advice for Taking Tadalafil with Metformin

If you are prescribed tadalafil while taking metformin, take each medicine exactly as directed. Tadalafil on-demand tablets (10 mg or 20 mg) should be taken at least 30 minutes before sexual activity, and you should not take more than one dose in 24 hours [4]. Daily tadalafil (2.5 mg or 5 mg) is taken once a day at the same time, regardless of when you plan to have sex. Metformin is usually taken with or after meals to reduce stomach upset; continue this routine as normal.

You do not need to time tadalafil around your metformin doses, as there is no interaction that requires separation. However, be mindful of alcohol: heavy drinking can worsen erectile dysfunction and increase the risk of low blood pressure when taking tadalafil [4]. It can also affect blood sugar control if you have diabetes. Grapefruit juice may increase tadalafil levels in your blood, so it is best avoided or limited.

Monitor how you feel, especially when you first start tadalafil. Common side effects include headache, indigestion, back pain, and flushing, which are usually mild and temporary [4]. If you experience dizziness or feel faint, sit or lie down and avoid driving or operating machinery. If you have an erection lasting more than four hours, sudden loss of vision or hearing, or chest pain during sex, seek urgent medical help immediately.

Reporting Side Effects

If you experience any side effects while taking tadalafil and metformin, tell your prescriber or pharmacist. You can also report side effects directly via the Yellow Card Scheme at www.mhra.gov.uk/yellowcard. Reporting helps improve the safety information available for all patients.

Other Medicines and Conditions to Discuss with Your Prescriber

While tadalafil and metformin can be taken together, your prescriber must know about every medicine you take—prescribed, over-the-counter, or herbal. Some medicines can interact with tadalafil in important ways. For example, potent CYP3A4 inhibitors (such as ritonavir, ketoconazole, itraconazole, or clarithromycin) can increase tadalafil levels, requiring a lower dose [4][12]. CYP3A4 inducers (such as rifampicin, carbamazepine, phenytoin, or St John's wort) can reduce tadalafil's effectiveness.

If you take alpha-blockers for prostate symptoms (such as tamsulosin or doxazosin), there is a risk of low blood pressure when combined with tadalafil. Your prescriber will ensure you are stable on the alpha-blocker and start you on the lowest dose of tadalafil [4]. Other blood pressure medicines can also add to the blood-pressure-lowering effect of tadalafil, so all must be declared during your consultation.

Tadalafil is not suitable if you have had a recent heart attack or stroke, unstable angina, severe heart failure, very low blood pressure, or a history of sudden vision loss (non-arteritic anterior ischaemic optic neuropathy, or NAION) [2][4]. Your prescriber will assess whether sexual activity is safe for you and whether tadalafil is appropriate. Never take tadalafil with nitrates, nicorandil, riociguat, poppers, or another PDE5 inhibitor, as these combinations are dangerous.

When to See Your GP

If you have new or worsening erectile dysfunction, it is important to see your GP for a full assessment. ED can be an early sign of cardiovascular disease or poorly controlled diabetes [1][2]. Your GP can check your blood sugar, blood pressure, cholesterol, and overall heart health, and refer you for specialist care if needed. Treating the underlying cause—such as optimising diabetes control—can improve erectile function alongside any ED treatment.

In summary

• Tadalafil and metformin can generally be taken together with no major direct interaction.
• Your prescriber will assess your diabetes control and cardiovascular health before prescribing tadalafil.
• Never take tadalafil with nitrates, nicorandil, riociguat, or poppers—this is dangerous.
• Optimising blood sugar control can improve erectile function alongside tadalafil treatment.
• Always declare all current medicines during your consultation, including metformin and any other diabetes treatments.

Faq