Does Sildenafil Lower Blood Pressure, and Why It Treats Pulmonary Hypertension

Yes, sildenafil lowers blood pressure. It has vasodilator properties, resulting in mild and transient decreases in blood pressure, and the mean maximum decrease in supine systolic blood pressure at the highest strength was 8.4 mmHg.

That vasodilator action helps explain several of the important precautions associated with the medicine.

It explains why sildenafil is dangerous with nitrates, including amyl nitrite. It explains why low blood pressure is a reason not to take it. And it explains why a separate sildenafil product is licensed to treat pulmonary arterial hypertension, a condition of raised pressure in the blood vessels of the lungs.

It also explains the most important warning here, which this page will state plainly rather than hint at. The sildenafil tablets licensed for erectile dysfunction are not a treatment for pulmonary hypertension. They are a different product, at a different strength, taken differently, under specialist care. Using one in place of the other is not a shortcut, and we will not present it as one.

Key things to know

• Sildenafil has vasodilator properties. It relaxes vascular smooth muscle, widening blood vessels and producing a mild, temporary reduction in blood pressure
• The mean maximum decrease in supine systolic blood pressure at the highest strength was 8.4 mmHg, with a diastolic change of 5.5 mmHg
• Sildenafil is not a nitrate. It is a phosphodiesterase type 5 inhibitor, a different class entirely
• A separate product is licensed to treat pulmonary arterial hypertension, authorised for adults and children aged 1 to 17
• Low blood pressure is a contraindication, as is high blood pressure that is not controlled. People with significant cardiovascular disease should have their suitability assessed by a clinician
• A trial of sildenafil during pregnancy was stopped early after a higher incidence of persistent pulmonary hypertension of the newborn and neonatal deaths was observed in the sildenafil group
• Altitude sickness and Raynaud's phenomenon are not licensed UK uses of sildenafil

Does Sildenafil Lower Blood Pressure?

By How Much?

The documented figures are specific. The mean maximum decrease in supine systolic blood pressure following dosing at the highest strength was 8.4 mmHg, and the corresponding change in supine diastolic blood pressure was 5.5 mmHg.

The regulator's own characterisation matters as much as the number. Sildenafil causes mild and transient decreases in blood pressure which, in the majority of cases, do not translate into clinical effects.

Read that carefully, because it does two things at once. It confirms the effect is real and measurable, and it says that for most people it produces no noticeable consequence at all.

A reduction of around 8 mmHg is generally modest, but its significance depends on your starting blood pressure and other factors that may also lower it. It becomes significant only when something else is pushing in the same direction, or when your starting pressure leaves no room for it.

Does It Happen to Everyone?

Sildenafil has vasodilator effects, so it can lower blood pressure in anyone who takes it. How much it changes, and whether that becomes noticeable, varies between individuals.

The blood pressure effect is a property of how the medicine works rather than a side effect that happens to some people and not others.

Sildenafil relaxes vascular smooth muscle, the muscle layer in blood vessel walls. Relaxed vessel walls widen, and wider vessels carry the same volume of blood at slightly lower pressure. Because it acts on a signalling pathway found in blood vessels generally, the effect is not limited to the tissues involved in erectile function.

The reduction is usually mild and temporary, but it can become clinically important in some people, particularly when other factors or medicines also lower blood pressure.

How Long Does the Effect Last?

The blood pressure effect follows the medicine rather than outlasting it, and the word the product information uses is transient.

The relevant pharmacokinetics are documented. Peak plasma concentrations are reached within 30 to 120 minutes, with a median of 60 minutes, and the terminal phase half-life is 3 to 5 hours.

The product information describes the blood-pressure effect as transient but does not give a separate duration for it.

That is worth knowing for a practical reason. A new blood-pressure change the following day should not automatically be attributed to sildenafil, and is worth discussing with a healthcare professional.

The Hypotension Warning

Low blood pressure is a contraindication, not a caution.

Sildenafil should not be used by anyone with low blood pressure, or with high blood pressure that is not controlled. Both ends are exclusions, which surprises people who assume only one direction matters.

The symptoms of an excessive drop are worth recognising. Dizziness is a recognised side effect of sildenafil, while fainting is uncommon. Severe dizziness, fainting or collapse after taking sildenafil needs medical attention rather than waiting to see whether it passes.

Sildenafil With High Blood Pressure

People with poorly controlled high blood pressure should have their cardiovascular status assessed before sildenafil is prescribed.

The distinction is about the current reading and the medicines producing it, which is exactly what an assessment establishes. For the most commonly prescribed classes the evidence is reassuring: pooling of diuretics, beta blockers, ACE inhibitors and angiotensin II antagonists showed no difference in the side effect profile in patients taking sildenafil compared with placebo.

Sildenafil is not a treatment for high blood pressure and is not licensed for that purpose. It lowers blood pressure as a consequence of its mechanism, which is a different thing from being prescribed to do so.

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Is Sildenafil a Nitrate?

The Direct Answer

No. Sildenafil is not a nitrate. It belongs to a group of medicines called phosphodiesterase type 5 inhibitors, usually shortened to PDE5 inhibitors.

Nitrates are a separate class, used mainly for angina and chest pain. They include glyceryl trinitrate, isosorbide mononitrate, isosorbide dinitrate, nicorandil and amyl nitrite.

The two are so frequently confused that the confusion has its own consequence: people assume that because sildenafil interacts dangerously with nitrates, it must be one. The opposite is closer to the truth.

Why the Two Get Mixed Up

They act on the same biological pathway at two different points, and that is precisely why combining them is dangerous rather than redundant.

Here is the pathway in plain terms. Nitric oxide activates an enzyme called guanylate cyclase, which increases levels of a messenger called cyclic guanosine monophosphate, or cGMP. Higher cGMP relaxes blood vessels.

• Nitrates donate nitric oxide. They add fuel at the start of the pathway, driving cGMP up
• Sildenafil inhibits PDE5, the enzyme that breaks cGMP down. It removes the brake at the end of the pathway

One pushes harder on the accelerator, the other disables the brake. Neither is the other, and together they produce a far larger effect than either alone. That is why the combination may lead to a dangerous fall in blood pressure, and why it is an absolute exclusion with no safe interval.

Is Sildenafil a Vasodilator?

Yes. The product information states directly that sildenafil has vasodilator properties, resulting in mild and transient decreases in blood pressure.

A vasodilator is any substance that widens blood vessels. Sildenafil qualifies, but it is a particular kind of vasodilator, and the qualification matters.

It is selective. Sildenafil is a potent and selective inhibitor of PDE5, with selectivity over other phosphodiesterase enzymes that runs into the thousands of fold for some of them, so it acts relatively specifically rather than as a general-purpose vasodilator.

It is also conditional. It works by enhancing signalling through the cGMP pathway rather than directly relaxing blood vessels itself.

What Blood Vessel Dilation Explains

The dilation happens in vascular smooth muscle, and it is a consequence of raised cGMP rather than a direct action on the vessel.

Three documented consequences follow from that, and they are worth seeing together because they are usually presented as unrelated facts.

These effects can share the same underlying mechanism, although individual side effects can have more than one contributing factor.

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Pulmonary Hypertension and Sildenafil

Sildenafil for Pulmonary Arterial Hypertension

Sildenafil is licensed in the UK for pulmonary arterial hypertension, but as a separate product from the erectile dysfunction tablets.

Pulmonary arterial hypertension, usually shortened to PAH, raises blood pressure in the arteries carrying blood from the heart to the lungs. It is a serious condition managed by specialists, and it is not the same as ordinary high blood pressure.

The licensed PAH product is authorised for adults and children aged 1 to 17. That age range is worth noting, because the erectile dysfunction product is licensed only for adult men aged 18 or over and should not be given to anyone under 18.

Same active substance. Two different licences, two different products, two entirely different clinical situations.

Why the Same Molecule Serves Both

The reason is that the cGMP pathway it acts on operates in blood vessels generally, including those of the lungs.

In PAH the therapeutic aim is to relax the blood vessels of the lungs so that the heart has less resistance to pump against. Sildenafil raises cGMP by preventing its breakdown, and higher cGMP relaxes vascular smooth muscle.

The same mechanism that produces a mild general fall in blood pressure is, in this setting, the point of the treatment rather than a side effect of it.

That is genuinely elegant pharmacology, and it is also where people draw exactly the wrong conclusion.

Why ED Tablets Are Not a Pulmonary Hypertension Treatment

This needs a plain answer rather than a hedge. Do not use erectile dysfunction sildenafil to treat pulmonary hypertension. The reasons are specific.

The two products are not interchangeable, and the differences in strength and frequency are not adjustable at home. PAH is a serious condition where treatment is monitored, and substituting a different licensed product for the one prescribed is not a decision that can safely be made outside specialist care.

If you have PAH and you have questions about your treatment, those go to the specialist team managing it. Sildenafil supplied here is for the erectile dysfunction licence only, and this medicine should only be used under the supervision of an appropriately qualified prescriber.

Sildenafil and Newborn Pulmonary Hypertension

This is the section where the evidence points firmly in the opposite direction to the question, and it deserves to be stated without softening.

A clinical trial called STRIDER investigated the use of sildenafil in pregnancy for intrauterine growth restriction, a condition where a baby grows too slowly in the womb. The theory was that relaxing blood vessels might improve the blood supply reaching the baby.

The trial was stopped early because of a higher incidence of persistent pulmonary hypertension of the newborn, known as PPHN, and neonatal deaths.

The figures from the Dutch arm are these. In the sildenafil group there were 17 cases of PPHN in 64 babies, which is 27%, including 11 deaths. In the placebo group there were 3 cases in 58 babies, which is 5%, with no reported deaths.

So the honest answer to whether sildenafil treats pulmonary hypertension in newborns is that in this trial, sildenafil given during pregnancy was associated with more of that condition, not less, along with excess deaths. The MHRA advice following it was direct: sildenafil is not authorised for the treatment of intrauterine growth restriction.

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Off-Label Uses

What Off-Label Actually Means

Off-label use means using a medicine outside the indication, population, dose or route covered by its licence. Evidence may exist for some off-label uses, but the use is not covered by the medicine's marketing authorisation.

The STRIDER trial illustrates why a plausible biological mechanism does not, by itself, establish that an off-label use is safe or effective.

Sildenafil has two UK licences: erectile dysfunction in adult men, and pulmonary arterial hypertension. Anything else is off label.

Sildenafil for Altitude Sickness

Sildenafil is not licensed in the UK for altitude sickness, and this page does not support using it for that purpose.

The reasoning people apply is understandable. High altitude raises pressure in the lung arteries, and sildenafil is licensed to lower pressure in the lung arteries in PAH. The inference feels logical.

The problem is that the inference is not evidence. A licence for one condition does not transfer to another that shares a mechanism, because the licence rests on studies conducted in that specific population at that specific dosing. Altitude illness also carries risks that a blood pressure medicine does not address, and it can be fatal.

There is a second consideration specific to this use. Because sildenafil can lower blood pressure, people who are unwell or dehydrated at altitude should not self-medicate with it. Any use for altitude-related illness should be discussed with a healthcare professional.

Sildenafil for Raynaud's

Sildenafil is not licensed in the UK for Raynaud's phenomenon.

Raynaud's involves blood vessels in the fingers and toes narrowing sharply in response to cold or stress, causing colour changes, numbness and pain. Since sildenafil relaxes blood vessels, the theoretical appeal is again obvious.

Again, theoretical appeal is not a licence. Where a specialist considers sildenafil for Raynaud's, that is an off-label decision made with knowledge of the person's full circumstances, monitoring, and an understanding of the alternatives. It is not something to arrange by obtaining erectile dysfunction tablets.

When to Seek Help

Seek medical attention immediately for any of the following:

• Fainting or collapse, which can indicate a significant fall in blood pressure
• Severe dizziness that does not settle
• Chest pain during or after use. This is an emergency
• An erection lasting longer than 4 hours
• A sudden decrease or loss of vision, or of hearing
• An allergic reaction

If sildenafil has been taken with a nitrate, seek urgent medical advice, because the combination can cause a significant fall in blood pressure.

Anyone being treated for pulmonary arterial hypertension should direct questions about their treatment to the specialist team managing it, and should not change or supplement it independently.

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