Sildenafil is an erectile dysfunction medication (ED). It belongs to the phosphodiesterase type 5 (PDE5) inhibitor class of drugs, which work by increasing blood flow to the penis.

Pfizer initially developed and marketed sildenafil under the brand name Viagra for the treatment of ED. Since Pfizer's patent expired, generic versions of sildenafil have become available.

For ED, the usual recommended dose of sildenafil is 50 mg, taken as needed, about one hour before sexual activity. Depending on individual response and tolerability, the dose can be increased to 100 mg or decreased to 25 mg.

Sildenafil, like all medications, can cause side effects such as headaches, flushing, upset stomach, vision changes, and nasal congestion. It should not be combined with nitrates because the combination can result in a dangerous drop in blood pressure. Sildenafil should also be used with caution in patients who have certain medical conditions, such as severe heart or liver problems, or in those who are taking certain medications, such as alpha-blockers.

Further information about the medication visit the link:

https://www.nhs.uk/medicines/sildenafil-viagra/