Sildenafil With Blood Pressure and Heart Medicines

If you take something for your blood pressure or your heart, the question is not whether sildenafil is safe in general. It is which specific medicine is on your prescription, because the answers range from an absolute exclusion to a measured effect of a few mmHg that most people never notice.

This page gives the documented figure for each one. Amlodipine has a specific measured number. So does doxazosin. Ramipril and bisoprolol have a documented finding of no effect. Nitrates are in a different category altogether.

Two corrections are worth flagging before you read further, because both contradict what is widely published elsewhere.

Sildenafil does not slow your heart rate. It lowers blood pressure slightly, but single oral doses in healthy volunteers produced no clinically relevant effects on ECG, and sildenafil showed no effect on cardiac output. Those are different things, and they get conflated constantly.

There is no safe waiting interval with nitrates. No interval, washout period or number of hours appears in the reviewed product information, because nitrates are a contraindication rather than a scheduling problem. Any page giving you a specific number of hours to wait is supplying a figure the regulator has not published.

Key things to know

• Sildenafil causes mild and transient decreases in blood pressure which, in the majority of cases, do not translate into clinical effects
• At the highest strength the measured drop peaked at 8.4 mmHg systolic and 5.5 mmHg diastolic, taken lying down
• Heart rate is not the issue. No clinically relevant ECG effects, and no effect on cardiac output
• Amlodipine: a specific study measured an additional reduction of 8 mmHg systolic and 7 mmHg diastolic in hypertensive patients
• Doxazosin: additional supine reductions of 7/7, 9/5 and 8/4 mmHg were recorded
• Ramipril, bisoprolol and diuretics: no effect on sildenafil pharmacokinetics
• Nitrates, including GTN, isosorbide mononitrate and nicorandil, are an absolute exclusion. No waiting time makes it acceptable
• Treatment suitability depends on an individual clinical assessment

Does Sildenafil Lower Blood Pressure and Heart Rate?

The Documented Blood Pressure Figures

Sildenafil lowers blood pressure slightly in everyone who takes it, and the size of that drop is documented rather than left vague.

The mean maximum decrease in supine systolic blood pressure following dosing at the highest strength was 8.4 mmHg, with a corresponding change in supine diastolic blood pressure of 5.5 mmHg.

The regulator's own summary of what that means is more reassuring than the number alone suggests: sildenafil causes mild and transient decreases in blood pressure which, in the majority of cases, do not translate into clinical effects.

Two words there carry the weight. Mild, because a drop of that size is smaller than the change most people see between sitting and standing. And transient, because it follows the medicine and passes with it rather than lasting.

The Effect on Heart Rate

Sildenafil is not documented as lowering heart rate, and this is the most common misunderstanding in the whole topic.

Single oral doses up to the highest strength in healthy volunteers produced no clinically relevant effects on ECG. Sildenafil showed no effect on cardiac output, and did not impair blood flow through narrowed arteries of the heart.

That last finding deserves attention. In a small study of patients with severe coronary artery disease, sildenafil did not impair blood flow through stenosed coronary arteries.

The Low Blood Pressure Exclusion

Low blood pressure is a documented exclusion rather than a caution, and so is high blood pressure that is not controlled.

Both ends matter, and people usually only remember one. Uncontrolled high blood pressure is an exclusion because the cardiovascular system is already under strain. Low blood pressure is an exclusion because a further mild drop starts from a base that has no room for it.

The risk is not that sildenafil produces a large fall in most people. It is that a small fall matters much more when you are already at the low end than when you are not, and it matters more again if another medicine is pulling in the same direction.

People with poorly controlled hypertension or significant cardiovascular disease should have their suitability assessed by a clinician.

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The Nitrates: An Absolute Exclusion

Glyceryl Trinitrate

Glyceryl trinitrate, usually called GTN, must never be taken with sildenafil. This is a contraindication, not a caution, and it is the most serious interaction associated with the medicine.

Sildenafil can enhance the blood-pressure-lowering effect of nitrates through the same signalling pathway. Taken together, the effects add up and may lead to a dangerous fall in blood pressure.

GTN comes in several forms and all of them count:

• A spray used under the tongue
• Tablets dissolved under the tongue
• A patch worn on the skin
• Modified release tablets taken regularly

The GTN Spray Is the Form Most Often Missed

The spray is most often overlooked, because it is used occasionally rather than daily and often lives in a pocket or a drawer rather than in a weekly pill organiser.

Frequency changes nothing. A GTN spray used twice a year is an absolute exclusion in exactly the same way as a daily nitrate tablet.

If you have been given a GTN spray for chest pain, that is a fact your prescriber needs before any supply of sildenafil, even if you have never used it.

Isosorbide Mononitrate and Dinitrate

Isosorbide mononitrate is a nitrate and is an absolute exclusion with sildenafil. Isosorbide dinitrate is the same.

These are usually taken as regular daily tablets to prevent angina rather than to treat an attack, which means people think of them as background medication rather than as heart medicine. They are nitrates, and the exclusion applies in full.

Nicorandil

Nicorandil is the one that catches people out, and the reason is in its description.

It is a hybrid of a potassium channel activator and a nitrate, and because of the nitrate component it has the potential to result in a serious interaction with sildenafil.

Nothing in the name suggests a nitrate, and many people taking it do not know it contains one. It is prescribed for angina, so anyone with angina should check whether nicorandil is on their list and say so specifically by name.

Why There Is No Waiting Time

A contraindication means the two medicines are not combined at all. It does not mean they are combined carefully with a gap in between.

No interval after which nitrate use becomes safe appears in the reviewed product information, so patients should not try to work out a safe interval themselves.

This has a real consequence in an emergency, and it is worth understanding in advance. If you take sildenafil and later develop chest pain, the people treating you need to know you have taken it, because it changes what they can safely give you. That is a conversation to have with your own prescriber about what to do in that situation, rather than one to settle with a number from a website.

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Blood Pressure Medicines That Need Care

Doxazosin

Doxazosin is an alpha blocker, and alpha blockers are the one blood pressure class with a documented warning attached rather than a documented all clear.

Alpha blockers can increase the risk of symptomatic hypotension in some susceptible people, particularly during the first few hours after sildenafil. Additional supine reductions of 7/7, 9/5 and 8/4 mmHg were recorded when doxazosin and sildenafil were taken at the same moment by people already settled on doxazosin.

Read the phrase a few susceptible individuals carefully. It is not a prediction that this will happen to you. It is a statement that it happens to some people, which is why the combination needs a prescriber's knowledge rather than a blanket rule.

Being Stable on an Alpha Blocker First

There is specific documented advice here that most pages leave out entirely, and it is genuinely useful.

Patients should be stabilised on alpha blocker therapy before starting sildenafil. The stated reason is to minimise the potential for developing postural hypotension, meaning the dizziness some people feel on standing up quickly. A lower starting strength should also be considered.

The practical reading of that is about sequence rather than prohibition. Someone settled on doxazosin for months is in a different position from someone who started it last week or whose dose was recently changed.

If your alpha blocker has recently changed, that is worth mentioning at a consultation rather than assuming a previous assessment still applies.

Tamsulosin and Alfuzosin

Tamsulosin is an alpha blocker, so the same precaution applies.

It is worth its own mention because of who takes it. Tamsulosin is very commonly prescribed for the urinary symptoms of an enlarged prostate rather than for blood pressure. Plenty of men taking it do not think of themselves as being on a blood pressure medicine at all, and leave it off the list they give at a consultation.

If you take tamsulosin, alfuzosin or any other alpha blocker for prostate symptoms, it belongs on your medicines list.

Amlodipine

Sildenafil and amlodipine are not contraindicated together, but the combination can produce an additional reduction in blood pressure.

In a specific interaction study, where sildenafil at the highest strength was given with amlodipine in hypertensive patients, there was an additional reduction in supine systolic blood pressure of 8 mmHg, and a corresponding additional reduction in diastolic pressure of 7 mmHg.

Separately, calcium channel blockers as a class showed no effect on sildenafil pharmacokinetics, meaning amlodipine does not change how much sildenafil is in your bloodstream.

Those are two different findings and both matter. No pharmacokinetic interaction, so the medicine is not made stronger. A measured additive blood pressure effect of 8/7 mmHg, because both medicines lower blood pressure by their own mechanisms.

An additional 8/7 mmHg is a real number and also a modest one, comparable to the additional reductions measured with doxazosin. The difference between the two is not the size of the drop. It is that alpha blockers carry a documented warning about symptomatic hypotension and a documented instruction about being stable first, and amlodipine does not.

Its clinical relevance can still vary depending on your baseline blood pressure and other medicines. It matters more if your blood pressure already runs low, if you are on several medicines that lower it, or if you already get dizzy on standing.

Blood Pressure Medicines With No Documented Effect

Ramipril

Ramipril is an ACE inhibitor, and pooling of antihypertensive classes including ACE inhibitors showed no difference in the side effect profile in patients taking sildenafil compared with placebo.

That is the finding people actually want. It is not just that ramipril does not change sildenafil levels. It is that people on these medicines did not report more side effects than people on a dummy tablet.

Bisoprolol

No documented effect. Bisoprolol is a beta blocker, and beta-adrenoreceptor antagonists were included in the group showing no effect on sildenafil pharmacokinetics. Beta blockers were also in the pooled analysis showing no difference in side effect profile against placebo.

Beta blockers deserve a specific note because of the heart rate question. They can lower heart rate independently, but the available sildenafil data do not show clinically relevant ECG effects from sildenafil itself. The combination should still be reviewed as part of an overall cardiovascular assessment.

The Full Picture in One Table

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Dizziness and What It Means

Dizziness is a recognised side effect of sildenafil and can be more noticeable when blood pressure is also being lowered by other medicines.

The mechanism is straightforward addition rather than anything unusual. Both medicines lower blood pressure a little, and dizziness is what a mild drop feels like, particularly on standing up quickly.

Practical points that follow from the documented figures:

• The effect is transient and follows the medicine rather than lasting
• Standing up slowly gives your circulation time to adjust
• Dizziness that arrives with the tablet and passes with it fits the documented pattern
• Dizziness that is severe, or comes with chest pain, does not

If dizziness is troublesome, that is a reason to speak to a prescriber rather than to adjust anything yourself. Never take a different quantity or strength than the one on your dispensing label.

The Summary

For most blood pressure medicines, the documented answer is that the combination is not a barrier.

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. That covers the large majority of people on treatment for high blood pressure.

The exceptions are short and specific:

1. Nitrates and nicorandil are contraindicated because of the risk of excessive blood-pressure lowering. They are commonly used in the management of angina
2. Alpha blockers need you to be stable on them first
3. Amlodipine has a measured additive effect of 8/7 mmHg, which is worth knowing rather than worth worrying about
4. Low blood pressure is a contraindication, and people with poorly controlled hypertension or significant cardiovascular disease require individual assessment before sildenafil is prescribed

Your prescriber will determine the appropriate treatment. Our guide to what to avoid when taking sildenafil covers the non-medicine cautions that sit alongside these.

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