Sildenafil Side Effects and How Long They Usually Last
If you have just taken sildenafil and something feels off, the question you want answered is not a list. It is how long this lasts and whether it is serious.
The UK product information answers the first part in one sentence: side effects from sildenafil are usually mild to moderate and of short duration. That is the regulator's own summary, and it is the single most reassuring documented fact on this page.
The second part needs more care, because a small number of effects are not mild and do need action straight away. This page separates the two clearly: what is common and passes, what is rare, and the four specific warning signs where the instruction is to stop taking the medicine and seek medical attention immediately.
Everything here comes from UK product information for sildenafil. Where something is not documented, this page says so rather than filling the space.
Key things to know
- Side effects are documented as usually mild to moderate and of short duration
- Headache is the only very common effect, meaning it affects at least 1 in 10 people
- In controlled clinical trials, the discontinuation rate due to sildenafil was low and similar to placebo
- Four warning signs mean stop and seek medical attention immediately: chest pain, an erection lasting longer than 4 hours, sudden decrease or loss of vision, and signs of an allergic reaction
- Sildenafil lowers blood pressure slightly in everyone. It should never be combined with nitrates or nitric oxide donors
- It should not be used by people with severe cardiovascular disorders, including a heart attack or stroke within 6 months, unstable angina or severe cardiac failure
- Treatment suitability depends on an individual clinical assessment
How Sildenafil Works
Sildenafil is primarily used to treat erectile dysfunction by increasing blood flow to the penis during stimulation. It works by blocking the enzyme phosphodiesterase type 5, or PDE5, which promotes smooth muscle relaxation in the blood vessels of the penis.
It is also prescribed, under a separate licence, to treat pulmonary arterial hypertension by relaxing blood vessels in the lungs.
Take sildenafil at the prescribed dose, and tell your prescriber about any other medicines you take, particularly nitrates, or health conditions such as heart disease, kidney disease, liver disease, bleeding disorders or pulmonary veno-occlusive disease. Interactions can increase the risk of side effects.
Avoid grapefruit juice while taking sildenafil, as it can increase the concentration in your bloodstream and with it the risk of side effects.
How Long Do Sildenafil Side Effects Last?
Do They Go Away?
Yes, in the overwhelming majority of cases. The product information states that side effects are usually mild to moderate and of short duration. However, persistent or unusual symptoms should not be ignored, and may need to be discussed with a healthcare professional.
The strongest supporting evidence is the drop-out data. In controlled clinical trials, the discontinuation rate due to sildenafil was low and similar to placebo.
That is a meaningful comparison, because it means people taking sildenafil stopped because of side effects at roughly the same rate as people taking a dummy tablet. If the side effects were commonly severe or lasting, that number would separate.
There are exceptions, and they are covered in the serious and rare sections below. Those are not effects that resolve on their own while you wait.
How Long Does Each One Last in Practice?
The product information does not publish a duration in hours for each individual effect. It gives the general characterisation of short duration and leaves it there, so anyone quoting a precise number of hours per symptom is extrapolating.
What can be said with confidence comes from the way the medicine behaves in the body. Sildenafil has a terminal phase half-life of 3 to 5 hours, so blood levels fall steadily from around an hour after the tablet.
Effects driven by the medicine being present, such as flushing and a stuffy nose, track that decline rather than outlasting it. Side effects follow the medicine, and the medicine clears within hours rather than days.
Side Effects the Next Day
The product information does not describe a next-day side effect profile, and this absence is worth stating plainly rather than glossing over.
Because sildenafil has a relatively short half-life, its concentration falls substantially over time. However, individual clearance varies, so the amount remaining at 24 hours should not be used to predict whether a side effect will still be present. There is no documented mechanism by which a mild effect would newly appear the following morning.
If you are experiencing something the next day, treat that as a reason to speak to a prescriber rather than as an expected part of taking the medicine. It may be unrelated, and it may be worth reviewing alongside your other medicines.
Side Effects the First Time
The first tablet is when people notice the most, and that is a matter of expectation rather than a documented difference. The reviewed product information does not describe a distinct first-dose profile, and it does not document side effects reducing with repeated use.
What it does document is that the safety and effectiveness of sildenafil was maintained in long-term studies, and that there is no indication from controlled clinical trial or post-marketing data that patients develop dependence or addiction.
The practical point for a first tablet is knowing which sensations are on the expected list. A headache, warmth in the face, a blocked nose or slight indigestion are all documented common effects. Knowing that in advance is the difference between a mild evening and an alarming one.
The Most Common Side Effects
What They Feel Like
Headache is the only effect classed as very common, meaning it affects at least 1 in 10 people. It is also the effect people are least prepared for, because it is not obviously connected to what the medicine does.
The common group, affecting between 1 in 100 and 1 in 10 people, covers three clusters. Digestive effects are nausea and indigestion. Circulatory effects are facial flushing and hot flush, plus dizziness and a stuffy nose. Visual effects are a colour tinge to vision, blurred vision and general visual disturbance.
The colour tinge is the one that worries people most, and it needs explaining rather than listing. It happens because the medicine has a small amount of activity with an enzyme found in the retina as well as the one it targets. It is documented as a common effect and belongs in the mild, short-duration group rather than the emergency group.
A sudden decrease or loss of vision is an entirely different event and is covered below.
Side Effects by Frequency
Frequency categories are defined by the regulator, not by opinion, and reading them properly changes how alarming the list looks.
| Frequency band | What it means | Documented effects |
|---|---|---|
| Very common | At least 1 in 10 people | Headache |
| Common | 1 in 100 to 1 in 10 | Nausea, indigestion, stuffy nose, dizziness, facial flushing, hot flush, colour tinge to vision, blurred vision, visual disturbance |
| Uncommon | 1 in 1,000 to 1 in 100 | Vomiting, upper abdominal pain, reflux, skin rash, eye irritation, bloodshot or red eyes, eye pain, seeing flashes of light, visual brightness, light sensitivity, watery eyes, pounding heartbeat, rapid heartbeat, high blood pressure, low blood pressure |
| Rare | 1 in 10,000 to 1 in 1,000 | Fainting, stroke, heart attack, irregular heartbeat, temporary decreased blood flow to parts of the brain, bleeding at the back of the eye, double vision, reduced sharpness of vision, non-arteritic anterior ischaemic optic neuropathy, sudden decrease or loss of hearing |
The very common and common reactions are generally described as mild to moderate and short-lived. However, this does not mean that every individual symptom will resolve within a predictable timeframe.
Side Effects in Men
Sildenafil is licensed for erectile dysfunction in adult men aged 18 or over. It is also used for other conditions, including pulmonary arterial hypertension, where it may be prescribed to adults of different sexes.
That means every figure on this page is already the male side-effect profile for this use. There is no separate breakdown to compare, because the licensed population for this indication is men only.
Serious Side Effects and Warning Signs
The Four Warning Signs That Mean Stop Now
Several serious reactions require immediate medical attention:
- Chest pain. Do not treat this as indigestion or as a passing effect
- A persistent and sometimes painful erection lasting longer than 4 hours. Known as priapism, this is a medical emergency and does not resolve by waiting
- A sudden decrease or loss of vision. This is separate from the common colour tinge or blurring
- An allergic reaction. Symptoms are set out in full below
Serious skin reactions and seizures are also listed as serious adverse effects requiring urgent attention.
These are the reason this page exists in the shape it does. Everything else on the list can reasonably be described as something that passes. These cannot.
Allergic Reaction Symptoms
An allergic reaction is one of the four documented reasons to stop and seek medical attention immediately. The symptoms are listed specifically in the product information: sudden wheeziness, difficulty breathing or dizziness, and swelling of the eyelids, face, lips or throat.
Two of those overlap with far more common and far less serious effects, and the difference is worth being clear about. Dizziness on its own is a documented common effect. Dizziness together with wheeziness, breathing difficulty or any swelling is the pattern that indicates an allergic reaction. Swelling is the sign that changes the picture.
If those symptoms appear, this is an emergency. Seek medical attention immediately.
When to Stop Taking Sildenafil
Separately from the emergency list, there are situations where sildenafil should not be started or continued without a prescriber reviewing it.
It should not be used in patients with severe cardiovascular disorders, such as a recent heart attack or stroke within 6 months, unstable angina or severe cardiac failure. It must never be taken with nitrates or nitric oxide donors.
If your circumstances have changed since your last consultation, particularly a new heart condition, a new medicine or a hospital admission, that is a reason to speak to a prescriber before the next tablet. This medicine should only be used under the supervision of an appropriately qualified prescriber.
When to See a Prescriber
The four warning signs need immediate attention rather than an appointment. For everything else, the useful test is whether an effect is behaving the way the documentation describes.
| What you are experiencing | What to do |
|---|---|
| Chest pain, an erection over 4 hours, sudden vision loss, allergic symptoms | Stop and seek medical attention immediately |
| A common effect that is not settling within hours | Speak to a prescriber before the next tablet |
| Any effect appearing or persisting the next day | Speak to a prescriber, since this is not documented as expected |
| Sudden decrease or loss of hearing | Seek medical advice promptly, as this is a documented rare effect |
| Fainting, or a pounding or irregular heartbeat | Seek medical advice promptly |
| A mild headache, flushing or stuffy nose that settles | Documented as expected, worth mentioning at your next consultation |
Rare Side Effects
Rare Effects on Vision
The rare band covers bleeding at the back of the eye, double vision, reduced sharpness of vision, and non-arteritic anterior ischaemic optic neuropathy, usually shortened to NAION. Rare means between 1 in 10,000 and 1 in 1,000 people.
NAION is a condition affecting the optic nerve that can cause sudden vision loss, usually in one eye. It is the clinical reason sudden decrease or loss of vision sits on the stop-immediately list rather than the wait-and-see list.
Distinguishing this from the common visual effects matters. A colour tinge, brightness or general blurring that comes on gradually and settles is in the common band. Sudden loss, or a sudden change in one eye, is not.
Rare Effects on Hearing
Sudden decrease or loss of hearing is documented as a rare effect. It is not on the four-item stop-immediately list, but it is not something to monitor at home either.
If hearing changes suddenly after taking sildenafil, seek medical advice promptly. Sudden hearing changes are time-sensitive in general medicine, and this is documented as a recognised rare effect rather than a coincidence to be dismissed.
Effects on Blood Pressure and the Heart
Blood Pressure
Sildenafil lowers blood pressure slightly in everyone who takes it, not only in people who experience a side effect. That is a direct consequence of how it works, and the size of the effect is documented.
The mean maximum decrease in supine systolic blood pressure following oral dosing at the highest strength was 8.4 mmHg, with a corresponding change in supine diastolic blood pressure of 5.5 mmHg. For most people that is a small and unnoticeable shift.
It stops being small in two situations, and both are about interactions rather than the medicine alone.
Nitrates and nitric oxide donors are the absolute one. Taking sildenafil at the same time as nitrates or nitric oxide donors, such as glyceryl trinitrate, isosorbide mononitrate, nicorandil or amyl nitrite, can lead to a dangerous fall in blood pressure. This combination must never be used.
Alpha-blockers are the conditional one. Using sildenafil alongside alpha-blocker medicines may lead to symptomatic hypotension in a few susceptible individuals, meaning a sudden fall in blood pressure that can cause dizziness or fainting. The product information recommends a lower starting strength for people already taking an alpha-blocker. Your prescriber will determine the appropriate treatment.
The Heart
Cardiac events do appear in the documented list, and they sit in the rare band: stroke, heart attack, irregular heartbeat and temporary decreased blood flow to parts of the brain, all between 1 in 10,000 and 1 in 1,000. Pounding heartbeat and rapid heartbeat sit one band up, in the uncommon group.
The more useful safety information is not the frequency, it is the exclusion. Sildenafil should not be used in patients with severe cardiovascular disorders such as a recent heart attack or stroke within 6 months, unstable angina or severe cardiac failure.
This is the clinical reason a proper consultation matters before supply rather than after. A medicine that lowers blood pressure and is contraindicated with nitrates cannot safely be handed over without someone establishing your cardiac history and your current medicines.
Chest pain after taking sildenafil is on the stop-immediately list. It should never be attributed to indigestion, which is a separately documented common effect, without medical assessment.
Medicines That Change the Picture
Beyond nitrates and alpha-blockers, the reviewed product information flags several medicines that require advice before sildenafil is used, because they change how much of the medicine reaches the bloodstream or how it interacts with your circulation.
- Nitrates and nitric oxide donors, including glyceryl trinitrate, isosorbide mononitrate, nicorandil and amyl nitrite. Never to be combined
- Alpha-blockers, including alfuzosin, doxazosin and tamsulosin
- Medicines that inhibit the CYP3A4 enzyme, including cimetidine and saquinavir, which raise how much sildenafil reaches the bloodstream
- Antifungal medicines including itraconazole and ketoconazole
- The antibiotic erythromycin
Grapefruit belongs in the same conversation. The product information instruction is not to take sildenafil with grapefruit or grapefruit juice, because this can affect how the medicine works. Our sildenafil interactions guide works through each of these in more detail.
How to Reduce Sildenafil Side Effects
This is where honesty is more useful than a list of tips. The product information does not contain a set of instructions for reducing side effects. There is no documented technique, no recommended supplement and no timing trick published for this purpose.
What the documentation does support is a short list of things already known to affect how the medicine behaves, and therefore how strongly it acts.
- Do not exceed the once-daily maximum. The maximum recommended frequency is once per day, and the leaflet instruction is not to take more than one tablet a day. Never double up
- Give your prescriber a complete medicines list. Most of the avoidable problems on this page are interactions, not the medicine acting alone
- Avoid grapefruit and grapefruit juice, which is documented as able to affect how the medicine works
- Be honest about alcohol. Drinking excessive alcohol can temporarily reduce your ability to get an erection, and dizziness is a documented common effect that alcohol will not help
- Report the effect rather than adjusting the strength yourself. A strength change is a clinical decision, and so is a move to a different medicine
Anything beyond that list is not documented, and this page will not invent it.
What the Trial Data Shows
Reading the raw list is alarming in a way the trial data is not, and the gap between those two things is the most overlooked part of this topic.
The reviewed product information reports three findings that put the list in proportion. Side effects are usually mild to moderate and of short duration. In controlled clinical trials, the discontinuation rate due to sildenafil was low and similar to placebo. And the safety and effectiveness of sildenafil was maintained in long-term studies.
The middle one carries the most weight. A discontinuation rate similar to placebo means that, across the trial population, being on the real medicine did not drive people to stop at a meaningfully higher rate than being on a dummy tablet.
Side-effect lists are compiled by recording everything reported, including events that would have happened anyway. The drop-out rate is the measure that filters for effects people actually found intolerable.
What Is Not Documented
Stating the gaps is part of answering the question properly. In the reviewed product information for sildenafil, the following are not documented:
- No stated duration in hours for any individual side effect. The characterisation is short duration, without a per-symptom figure
- No next-day side effect profile
- No documented method for reducing side effects beyond the interaction and frequency guardrails already in the leaflet
- No documented difference in the side effect profile between one strength and another, other than the blood pressure measurement being taken at the highest strength
- No documented reduction in side effects with repeated use over time
- No documented separate profile by age, although clearance is reduced in people aged 65 or over, producing approximately 90% higher plasma concentrations
- No documented tolerance or dependence
That last point is worth holding on to. Because effectiveness is documented as maintained in long-term studies and dependence is not documented at all, a change in how you tolerate the medicine after months of use is a reason to speak to a prescriber about what else has changed, rather than something to expect.
Our guide to sildenafil long-term use covers what continued treatment involves.
Frequently Asked Questions
How long do sildenafil side effects usually last?
Which side effect is most likely?
When should someone stop taking sildenafil immediately?
What are the signs of an allergic reaction?
Does sildenafil affect blood pressure?
Is a colour tinge to vision serious?
Do the side effects get milder with repeated use?
Are side effects worse on a stronger tablet?
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