Oral minoxidil (low dose) and Sildenafil and other PDE5 inhibitors (tadalafil, vardenafil, avanafil)
CAUTION
CAUTION: neither the Loniten nor the Viagra SmPC names this pair, but the BNF lists minoxidil with sildenafil, tadalafil, vardenafil and avanafil as combinations where both medicines 'can increase the risk of hypotension'. It is an additive effect, not a ban: tell your prescriber, and take care the first time you combine them.
Mechanism
Both medicines widen blood vessels, by different routes. Minoxidil opens potassium channels in the smooth muscle of small arteries. Sildenafil and the other PDE5 inhibitors act through the nitric oxide pathway. The Viagra SmPC says sildenafil 'has vasodilator properties, resulting in mild and transient decreases in blood pressure', and that when sildenafil 100 mg was given with amlodipine, another vasodilating blood pressure medicine, supine systolic blood pressure fell by a further 8 mmHg on average. With alpha-blockers, it warns, the combination 'may lead to symptomatic hypotension'.
Neither SmPC mentions the other medicine. The BNF entry describes an additive effect based on how both medicines work, rather than a specific study of this pair. At the low doses of minoxidil used for hair loss the extra drop may be small for many people, but it is hard to predict for any individual, especially if you also take blood pressure medicines or alpha-blockers, or drink alcohol.
One combination is not a matter of caution. The Viagra SmPC contraindicates sildenafil with nitrates in any form or nitric oxide donors 'such as amyl nitrite' (poppers), because sildenafil potentiates their effect on blood pressure.
Practical advice
Tell your prescriber in your assessment if you use, or might use, sildenafil, tadalafil, vardenafil or avanafil, including any bought from a pharmacy. It is a routine question, and it will not be judged.
The first time you combine them, be somewhere you can sit or lie down, avoid heavy drinking, and get up slowly. Stop and sit down if you feel lightheaded, dizzy, faint or have blurred vision, which are the NHS symptoms of low blood pressure.
Never combine a PDE5 inhibitor with nitrates or poppers. This is a contraindication in its own right, whether or not you take minoxidil.
If erection problems are new, mention when they started. Finasteride and dutasteride carry MHRA warnings about sexual side effects that may persist after stopping (see dutasteride and sexual side effects), and the NHS lists high blood pressure, high cholesterol and diabetes among the causes of erection problems; our sister service can help investigate erectile changes.
Call 999 for chest pain, fainting that does not quickly resolve, or breathlessness. See also oral minoxidil and blood pressure medicines and oral minoxidil and cardiovascular effects.