Sildenafil

Sildenafil is the best-known PDE-5 inhibitor and became world-famous under the brand name Viagra. It is used for erectile function and is one of the most studied compounds there is.

It is taken as a tablet on demand, about half an hour to an hour before the desired effect. Sildenafil works relatively fast over a medium time window, which makes it the classic "shortly before" option.

An erection happens when a messenger (cGMP) relaxes the blood vessels in the penis so more blood flows in. The enzyme PDE-5 breaks that messenger down again. Sildenafil blocks PDE-5, so the signal lasts longer and the erection comes more easily and stays more stable.

Important: sildenafil does not replace sexual arousal, it only amplifies the natural response. Without stimulation, nothing happens.

Sildenafil is swallowed as a tablet, about 30 to 60 minutes before activity.

• A fatty meal noticeably delays and weakens the effect. So take it with some gap from food, ideally on a fairly empty stomach.
• At most once a day.
• Larger amounts of alcohol can worsen the effect.

The two most-compared PDE-5 inhibitors. The core difference is duration:

• Sildenafil lasts about 4 to 6 hours, fast onset, classically taken shortly before. More sensitive to fatty food.
• Tadalafil lasts up to 36 hours (the "weekend pill") and decouples dosing in time from activity. Less sensitive to food, can also be dosed low daily.

In short: sildenafil for planned, single occasions, tadalafil for more spontaneity over a longer window. Which fits better is individual.

Sildenafil is extremely well evidenced. In the approval study (Goldstein, 1998), the success rate rose clearly with dose, with about 69 percent of attempts successful in the dose-escalation group versus 22 percent on placebo. On this basis sildenafil was approved and has since been studied and used millions of times.

The study with a link is in the source block below.

The most common effects are mild and come from the mechanism: headache, facial flush, a stuffy nose, sometimes heartburn. Occasionally a blue-tinged or blurred vision that passes. Most effects are dose-dependent.

One point is non-negotiable and the most important here: PDE-5 inhibitors must never be combined with nitrates. That includes heart nitrates (e.g. nitroglycerin) and also "poppers" (amyl nitrite). The combination can drop blood pressure dangerously.

Caution also with alpha-blockers (blood pressure) and with existing cardiovascular disease. Anyone with pre-existing conditions or on medication should clear it with a doctor first. This is not an area for experiments.

Store the tablets dry, at room temperature and protected from light, out of reach of children. Keep the original packaging closed and mind the expiry date.