BMA Concise Guide to Medicine & Drugs


Brand names [sildenafil] Revatio, Viagra; [tadalafil] Cialis

Used in the following combined preparations None


Drug group Drug for erectile dysfunction

Overdose danger rating Medium

Dependence rating Low

Prescription needed Yes (except for Viagra for some men)

Available as generic No


Sildenafil and tadalafil are used to treat erectile dysfunction. They do not cause an erection directly but prevent the muscle walls of the blood-filled chambers in the penis from relaxing. They do not need to be taken regularly, only before sexual activity. Sildenafil is also occasionally used to treat pulmonary hypertension (high blood pressure in the arteries supplying the lungs). Because sildenafil and tadalafil are vasodilators, they can cause a small fall in blood pressure and may increase the effect of antihypertensive drugs. They should not be taken if you are using a nitrate because they greatly increase its effects.

Viagra (a brand of sildenafil) is available over-the-counter to men aged 40–65 who pass a medical check by the pharmacist.


Your drug prescription is tailored for you. Do not alter dosage without checking with your doctor.

How taken/used Tablets.

Frequency and timing of doses Erectile dysfunction As needed; maximum one dose daily, 1 hour before sexual activity. Pulmonary hypertension 3 x daily.

Adult dosage range Erectile dysfunction (sildenafil) 25–100mg per dose; (tadalafil) 10–20mg per dose. Pulmonary hypertension (sildenafil) 60mg daily.

Onset of effect 30 minutes.

Duration of action 4 hours (sildenafil); up to 36 hours (tadalafil).

Diet advice None, although the drugs take longer to work after a meal, especially a high-fat meal.

Storage Keep in original container at room temperature out of the reach of children.

Missed dose For erectile dysfunction, the drugs are used only when needed. For pulmonary hypertension, take as soon as you remember then take the next dose as scheduled.

Stopping the drug For erectile dysfunction, the drugs can safely by stopped as soon as no longer needed. For pulmonary hypertension, do not stop without consulting your doctor; your condition may worsen.

Exceeding the dose An occasional unintentional extra dose is unlikely to cause problems. Large overdoses may cause headache, dizziness, flushing, and altered vision. Notify your doctor.


Adverse effects are common, although not usually severe. They include headache, flushing, dizziness, indigestion, nasal congestion, blurred vision, and altered colour vision. Discuss with your doctor if any of these are severe. If a painful erection lasting more than 4 hours or chest pain occur, stop taking the drug and seek immediate medical attention.


Nitrates The effects of these drugs are greatly increased by sildenafil and tadalafil and they are therefore not prescribed with sildenafil or tadalafil.

Antihypertensive drugs Sildenafil and tadalafil may enhance the blood-pressure-lowering effect of these drugs.

Cimetidine, erythromycin, nicorandil, ketoconazole (oral), and antivirals These drugs increase the blood levels and toxicity of sildenafil and tadalafil.


Be sure to tell your doctor if:

· You have heart problems.

· You have had a stroke or heart attack.

· You have liver or kidney problems.

· You have low or high blood pressure.

· You have sickle cell anaemia, leukaemia, or myeloma.

· You have an inherited eye problem.

· You have an abnormality of the penis.

· You are taking other medicines, especially a nitrate drug.

Pregnancy Not prescribed.

Breast-feeding Not prescribed.

Infants and children Not prescribed under 18 years, except rarely for pulmonary hypertension on specialist advice.

Over 60 Reduced dose may be necessary.

Driving and hazardous work Avoid such activities until you have learned how sildenafil or tadalafil affects you because they can cause dizziness and altered vision.

Alcohol No special problems.


No problems expected.