Because it improves blood flow to the penis, Viagra (sildenafil citrate) treats erectile dysfunction (ED) effectively. But now that the "little blue pill" is more accessible, some men might use it recreationally – meaning without a prescription. Men may take it socially with other drugs, rather than for treatment of a medical condition. A study in the Archives of Sexual Behavior says that recreational ED drug use is associated with increased risk of sexually transmitted infections and higher rates of illegal drug use.

But the side effects of sildenafil citrate, even with a prescription, can be intense. Think headaches, upset stomach, blue-tinted vision, flushing, diarrhea, difficulty sleeping or dizziness. According to urologist Chris Deibert, MD, MPH, "Without a physical examination or medical supervision, the side effects plus any health risks can be dangerous." For men with pre-existing heart disease, sildenafil citrate can make their condition worse.

For example, if someone takes sildenafil citrate after a night of drinking, they can experience migraines and increased facial flushing. Since alcohol decreases blood flow to the penis, it limits the drug's effectiveness (i.e. an erection's rigidity).

Can sildenafil citrate cause erectile dysfunction?

The Journal of Sexual Medicine found that men who take ED medications recreationally report lower sexual satisfaction than nonusers. The more frequently men used ED medications recreationally, the less confident they were in their sexual abilities. Recreational ED drug use can even cause "psychogenic erectile dysfunction". In psychogenic erectile dysfunction, psychological issues prevent maintaining or getting an erection – nothing physical. 

Taking sildenafil citrate with other drugs like cocaine

Mixing ED drugs with hard drugs is inherently dangerous. For example, cocaine constricts blood vessels, and sildenafil citrate does the opposite.
"Don't mix Viagra with other drugs," says Dr. Deibert. "Inconvenient side effects of Viagra on its own – like vision changes or dizziness – are common. But if someone takes Viagra with cocaine, they're at risk for priapism, heart attack or stroke." Priapism is an erection that lasts more than four hours and requires urgent medical attention to reverse.

Expired, fake and contaminated pills

Another problem is how people are getting the drug. If you don't have a prescription, the drug itself – not just how you use it – may be a problem. Getting drugs from a friend or other sources is a recipe for expired, fake or contaminated pills. Online pharmacies don't always hold up to scrutiny, either. Often they sell drugs with missing active ingredients or in smaller amounts.

The bottom line: It's safe to take as prescribed. The danger comes from taking it with other drugs or getting it from someone without a medical license.