Erectile dysfunction medicines: safety, interactions and online supply risks

The main group is the phosphodiesterase type 5 inhibitors, which include sildenafil, tadalafil, vardenafil and avanafil. They differ in how quickly they act and how long they last. In the UK some can be supplied by a pharmacist after a consultation, and others require a prescription. The right choice depends on your health, other medicines and how you want to use them. A clinician or pharmacist can explain.

• Anyone taking nitrates or nicorandil, such as for angina.

• People with severe heart disease, recent heart attack or stroke, or very low blood pressure.

• Those with severe liver or kidney impairment, where dose adjustments are needed.

• People with certain eye conditions, such as retinitis pigmentosa.

• Men who have had sudden vision loss in one eye related to optic nerve problems.

• Men taking alpha-blockers or other blood pressure medicines, where dose and timing matter.

• Men whose doctors have advised against sexual activity because of heart problems.

Common effects include headache, flushing, nasal congestion, indigestion, dizziness and, with some, back or muscle aches. Rare but serious effects include sudden loss of vision, sudden hearing loss and prolonged painful erection (priapism). Seek urgent medical help for an erection lasting more than four hours, sudden vision or hearing changes or chest pain. Tell emergency staff that you have taken a PDE5 inhibitor, particularly because they may need to avoid nitrates.

Some antifungals, antibiotics and HIV medicines raise PDE5 inhibitor levels, as does grapefruit juice in excess. Recreational drugs known as poppers (alkyl nitrites) can cause a severe drop in blood pressure when combined with these tablets. Alcohol and heavy meals may affect response or increase side effects. Always tell the prescriber or pharmacist about every medicine you use.

Counterfeit tablets are sold online and may contain no active ingredient, the wrong dose or other drugs, including undeclared substances. Some herbal "male enhancement" products have been found to contain undeclared prescription drugs. Using them risks serious interactions. Obtain medicines only from a registered pharmacy that requires a proper consultation, and avoid products offered without any health questions. Report suspected counterfeit products to the MHRA.

A registered pharmacy displays its registration details and a named superintendent pharmacist. The General Pharmaceutical Council register lets you check. A consultation should ask about your heart health, blood pressure, medicines and previous reactions. If a seller offers tablets with no questions, treat that as a warning sign.

Be ready to tell the pharmacist or prescriber about your heart history, blood pressure, all medicines including over-the-counter and recreational products, any previous reaction to similar tablets and any eye problems. Ask which medicine they recommend, how to take it, how soon to expect an effect and what to do if it does not work. Ask what to do in an emergency. If you cannot talk openly in a particular setting, a different pharmacy or a GP appointment may be easier. Honest answers keep you safe.