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Sildenafil – what the active substance can do

by Josephine Andrews
Published: Last Updated on 260 views

The active ingredient sildenafil has a potency-stimulating effect and is therefore used against erectile dysfunction (impotence). It is also used for pulmonary hypertension. The potency-enhancing effect of sildenafil was discovered by accident, because a new heart drug was originally sought. Here you can read everything you need to know about the effects, side effects and use of Sildenafil.

This is how Sildenafil works

Sildenafil is a so-called PDE-5 inhibitor (phosphodiesterase-5 inhibitor). It inactivates the enzyme PDE-5 so that the erection-promoting cyclic guanosine monophosphate (cGMP) is no longer broken down. The result: the blood vessels remain relaxed and the ability to have an erection improves. Accordingly, sildenafil has a vasodilating and blood pressure-lowering effect.

During sexual stimulation, the neurotransmitter nitrogen oxide (NO) is released in the erectile tissue of the penis. NO increases the amount of another messenger substance, the so-called cGMP. As a result, the muscles in the erectile tissue relax and the blood vessels widen. This allows more blood to flow in, leading to an erection . Finally, the cGMP is broken down by the enzyme PDE-5, which constricts the vessels again – the penis relaxes.

PDE-5 inhibitors such as sildenafil also exert their vasodilating effect in the lungs . They can therefore counteract high blood pressure (pulmonary hypertension) that prevails there .

intake, degradation and excretion

The active substance reaches its maximum concentration in the blood plasma around 60 minutes after ingestion. Four hours after ingestion, half of the active ingredient has already been broken down again. The liver is mainly responsible for the breakdown .

When is Sildenafil used?

Sildenafil is primarily used for erectile dysfunction (ED, impotence ). This is when a man has not been able to achieve or maintain an erection for a period of at least six months.

Recently, sildenafil has also been used to treat pulmonary hypertension (pulmonary hypertension) . It has been approved for this application in the EU and Switzerland since 2006.

How Sildenafil is used

Sildenafil is mainly used in tablet form. Ingestion is usually started with the lowest dose.

For erectile dysfunction (ED), one tablet is taken about an hour before sexual intercourse. If necessary, the dosage can be increased in consultation with the doctor. The maximum sildenafil dosage for ED is 100 milligrams per day and must not be exceeded. The dosage must be adjusted in the elderly and in patients with liver and kidney failure.

The intake should be started here with 25 milligrams. A dose increase is possible in consultation with the doctor. The preparations usually contain the active ingredient in the form of salts (sildenafil citrate).

What are the side effects of Sildenafil?

Very common side effects are headaches , skin reddening (flushing) that occurs in attacks, and visual disturbances with sensitivity to light and blurred vision. In addition, there is often a blocked nose , dizziness and an acute skin rash (exanthema).

Very serious undesirable effects from the sexual enhancer are heart attack and sudden cardiac death, stroke (apoplexy) and the occlusion of retinal vessels.

In the past there have been many deaths in connection with taking the sexual enhancer, for example due to a heart attack. Therefore, before using Sildenafil, the contraindications (contraindications) must be observed.

What should be considered when taking Sildenafil?


Sildenafil should not be taken if:

  • Hypersensitivity to the active substance or any of the components
  • recent heart attack or stroke
  • severe cardiovascular diseases such as cardiac insufficiency ( heart failure ) or unstable angina pectoris (chest tightness)
  • concomitant intake of nitrates (e.g. nitroglycerin, ISMN) or other NO donors (e.g. molsidomine , riociguat)
  • low blood pressure (less than 90/50 mmHg)
  • Eye diseases such as ischemic optic neuropathy or hereditary diseases of the retina (e.g. retinitis pigmentosa )
  • severe hepatic or renal impairment


The simultaneous use of vasodilating drugs such as so-called NO donors (e.g. nitrates, molsidomine, nicorandil, amyl nitrite, sodium nitroprusside) can significantly reduce blood pressure. Therefore, in order to avoid life-threatening consequences, Sildenafil must not be used together with such drugs.

For the same reason, patients with a heart attack who have previously taken sildenafil should not be treated with nitrates in an emergency. Blood pressure is also dangerously reduced in combination with high blood pressure medication such as so-called alpha blockers (e.g. doxazosin ).

Sildenafil is primarily metabolised in the liver by certain hepatic enzymes (CYP3A4 and to a lesser extent CYP2C9). These enzymes can be inhibited by some drugs (CYP inhibitors), which can increase both the effect and the side effects of sildenafil enormously.

For this reason, the sexual enhancer must not be used together with CYP3A4 inhibitors. These include, for example, the antifungal drugs ketoconazole and itraconazole, the antibiotic erythromycin, the gastric drug cimetidine and the HIV drugs saquinavir and ritonavir.

The activity of the liver enzymes can also be increased by some drugs (CYP inducers). This reduces the effectiveness of sildenafil. Examples of CYP3A4 inducers include the epilepsy drugs phenobarbital, phenytoin , and carbamazepine . But St. John’s wort can also accelerate the breakdown of sildenafil and thus weaken its effect.

age restriction

Sildenafil medication for the treatment of pulmonary hypertension (pulmonary arterial hypertension) can be used in children from the age of one year. In this indication, women also receive the active ingredient.

Drugs for the treatment of erectile dysfunction, on the other hand, are only approved for male adults over the age of 18.

pregnancy and breast feeding period

The experience of taking sildenafil during pregnancy and breastfeeding is extremely limited, since the active ingredient has only recently been approved for women of childbearing age. Due to the lack of data, the specialist information advises against taking it. If an application is absolutely necessary, a strict benefit-risk assessment is required.

How to get medication with sildenafil

Sildenafil can only be bought on prescription in Germany, Austria and Switzerland, so it requires a prescription.

Before prescribing, the doctor will examine the patient if they are at particular risk of developing certain side effects due to pre-existing conditions (such as heart problems).

The prescription requirement applies not only to the original preparation, but also to sildenafil generics. Although you can buy the sexual enhancer on the Internet without a prescription, this is illegal. Above all, with such preparations, neither the sildenafil dosage nor the purity and thus the effect and safety are guaranteed. It is therefore not advisable to buy the sexual enhancer over the Internet without a prescription.

Since when is Sildenafil known?

Sildenafil, the well-known blue pill , was developed in the 1990s. The active ingredient was approved in the EU and Switzerland in 1998.

In 2013, the patent protection of the sexual enhancer expired in Germany. Since then, numerous sildenafil generics have been on the market. In the US, the patent for sildenafil only expired in 2019.

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