Harvard Men's Health Watch

Viagra precautions

Q. I am a 64-year-old man. Aside from diabetes, I've been healthy and until now, the only prescription I've taken is insulin. But I've been having trouble with erections, and my doctor just gave me a prescription for Viagra. He also told me to be careful about using other drugs with Viagra but didn't give me a list. Can you please fill me in?

A. Viagra (sildenafil) is one of three widely used medications for erectile dysfunction; the others are Levitra (vardenafil) and Cialis (tadalafil). Although you'd never know it from their advertisements, the three medications are closely related and have similar — and very favorable — track records for effectiveness and safety. They also have similar drug interactions and require similar precautions.

The first and most important precaution involves nitrate drugs, including prescription drugs used for angina, which are taken in a variety of different ways: under the tongue, in pills, skin patches, through inhalers, or intravenously. The precaution also applies to the "recreational" use of inhaled nitrates, often referred to as "poppers." This warning applies to all nitrates and all ED pills, and the rule is simple: they don't mix. The problem is a potentially life-threatening fall in blood pressure. Men should not take a nitrate within 24 hours of using Viagra or Levitra or within 48 hours of taking Cialis, which stays in the body longer than the others.

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