What is Viagra? 

Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. Viagra is approved for this use in males ages 18 years and older.

How does sildenafil work?

Viagra contains the drug sildenafil. It belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors. (A class of drugs is a group of medications that act in a similar way.) Viagra works by increasing blood flow to your penis, which helps you have and keep an erection. But this drug only works if you’re sexually aroused.

What dose should you take?

Viagra is available in two doses: 50mg and 100mg.

50mg
The starting dose usually recommended for men taking Viagra for the first time.

100mg
A high-strength dose used if you find 50mg isn’t effective enough, or your erection lasts less than 4 hours

What drugs will affect Viagra?

Do not take Viagra with similar medications such as avanafil (Stendra), tadalafil (Cialis) or vardenafil (Levitra). 

• drugs to treat high blood pressure or a prostate disorder;

• an antibiotic - clarithromycin, erythromycin, or telithromycin;

• antifungal medicine - ketoconazole or itraconazole; or

• medicine to treat HIV/AIDS - atazanavir, indinavir, ritonavir, or saquinavir;

• nitrates;

• medications used to treat pulmonary artery hypertension.

Does sildenafil have side effects?

The most common side effects of sildenafil include:

• headache
• indigestion or heartburn
• back pain
• muscle aches
• flushed skin
• stuffy or runny nose

These side effects usually go away after a few hours.

Very occasionally, sildenafil can cause a painful erection or an erection that won’t go away (priapism).