Sildenafil (the Viagra ingredient): what the label says

Sildenafil is the active ingredient in Viagra. The US label lists one use: erectile dysfunction.

It does not create an erection by itself. The label says that at recommended doses it has no effect without sexual stimulation.

This is general label information, not personal medical advice.

The US Viagra label gives 50 mg as the usual dose, taken as needed about 1 hour before sexual activity. It can be taken anywhere from 30 minutes to 4 hours before. The most it allows is once per day.

A prescriber may raise the dose to a maximum of 100 mg or lower it to 25 mg depending on effect and tolerance. It can be taken with or without food.

For some people the label suggests a lower starting point:

• Anyone using a nitrate medicine in any form, such as a nitroglycerin tablet for chest pain. The label contraindicates it because blood pressure can fall sharply. MedlinePlus adds that some recreational drugs contain nitrates and are dangerous with sildenafil too.
• Anyone using riociguat, a guanylate cyclase stimulator.
• Anyone whose doctor has judged sexual activity unsafe because of heart or circulation problems.

The label also advises caution with alpha-blockers, because both can lower blood pressure.

The label lists these as most common (over 2% in trials): headache, flushing, indigestion, abnormal vision, stuffy nose, back pain, muscle pain, nausea, dizziness and rash.

Examples from the label, as percent of people affected:

Side effects tend to be more frequent at higher strengths.

• An erection lasting more than 4 hours, or a painful one. Untreated, it can damage tissue.
• Sudden loss of vision in one or both eyes. The label says this can be a sign of NAION, a rare condition.
• Sudden decrease or loss of hearing, sometimes with ringing or dizziness.
• Chest pain or worsening shortness of breath.
• Signs of allergy, such as rash, swelling or trouble breathing.

People with heart disease, or who have had vision problems like this before, should talk to a doctor first. The label notes that sexual activity itself carries some cardiac risk in people with existing heart and vascular disease.

Sildenafil comes as tablets, oral jelly, effervescent tablets and chewables. The shop's examples include Malegra 100, Sidegra 50 and 100, and Kamagra in jelly, effervescent and chewable form.

The dose information above comes from the Viagra tablet label (25, 50 and 100 mg). For another form or brand, follow the leaflet inside that pack.

Strength matters because 100 mg is the highest dose the Viagra label recommends, and the label sets a maximum of once per day. That is why using several products on the same day is not advised. Check that the name, strength and form match what your doctor or pharmacist recommended.

• Before starting, especially if you take chest-pain medicine, blood pressure tablets, antifungals or HIV medicine.
• If you have heart disease, low blood pressure, liver or kidney disease, or past eye problems.
• If side effects bother you, or you are unsure which strength is right.
• If any symptom in the urgent list above appears, go to a hospital straight away.