Sildenafil: Contraindications & Drug Interactions

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will briefly describe a drug called sildenafil before discussing its major contraindications. You'll also learn about some of its various drug interactions.


If you've heard of Viagra, then you've also heard of sildenafil. That's because sildenafil is simply the generic name for the brand name medication of Viagra (as well as Revatio). And if you know anything about Viagra, then you know it's used to treat erectile dysfunction (impotence). Oh, and by the way, Revatio is also used to treat pulmonary hypertension (high blood pressure) within the blood vessels of the body.

Since taking any drug poses certain risks, there are some people who shouldn't take sildenafil. Similarly, taking sildenafil while on other medications can increase the risks of experiencing its (or the other drug's) side effects. In that case, why don't we explore sildenafil's contraindications and drug interactions?


First, you should know that the term 'contraindications' is a fancy way of saying 'instances when this drug shouldn't be used'.

The first major contraindication to sildenafil is a known hypersensitivity to the medication. In other words, an allergic reaction to it. This can present itself in many ways. For instance, someone who has taken sildenafil in the past may have experienced a rash, hives, swollen tongue, or other signs that they are allergic to it.

Another important contraindication is the use of nitrates. Nitrates are drugs that dilate our blood vessels. And, lo and behold, sildenafil does much the same! Sildenafil appears to make nitrates more potent than they otherwise may have been intended to be in a patient. This can lead to the over-dilation of the blood vessels, which in turn can lead to a dangerous drop in a person's blood pressure. Actually, let's stress that a bit more; the drop in blood pressure can be fatal if these drugs are taken together.

A similar effect is possible in people who use guanylate cyclase stimulators, like riociguat. Guanylate cyclase stimulators are drugs that help lower a person's blood pressure, especially in their lungs. Again, the simultaneous use of guanylate cyclase stimulators is a contraindication to the simultaneous use of sildenafil since the additive drop in blood pressure caused by both of these types of drugs can prove fatal.

Drug Interactions

Sildenafil has numerous other possible drug interactions. We can't possibly cover all of them, but here are a sample of interactions to keep in mind:

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