Most side effects from ED tablets like sildenafil and tadalafil are mild, short-lived and directly explained by how the medicines work: they widen blood vessels — everywhere, not just where you want. Headache, facial flushing, a stuffy nose and indigestion are the classic quartet. A small number of symptoms, though, are genuine emergencies. Here's how to tell the difference.
Why side effects happen
PDE5 inhibitors block the enzyme that reins in blood-vessel relaxation. That's the therapeutic effect in the penis — and the side-effect profile everywhere else: vessels in the face flush, vessels in the nasal lining swell (blocked nose), vessels around the brain dilate (headache). Understanding this makes the common effects less alarming: they're the medicine working, felt in the wrong places, and they pass as the dose wears off.
Normal and expected
- Headache — the most common effect of both medicines. Hydration helps; paracetamol is fine alongside if needed
- Facial flushing — warmth or redness in the face and chest, harmless and temporary
- Blocked or runny nose — nasal congestion from vessel dilation, fades with the dose
- Indigestion or heartburn — relaxed muscle includes the valve at the top of the stomach; avoid lying flat straight after eating
- Mild dizziness — usually blood-pressure related; stand up slowly, avoid combining with lots of alcohol
- Sildenafil-specific: temporary visual tint — a bluish tinge or extra light sensitivity for a few hours; odd but not dangerous, and a reason some men prefer tadalafil
- Tadalafil-specific: back pain or muscle aches — appears 12–24 hours after dosing in some men, consistent with its long action, and settles
These typically last no longer than the medicine's active window (hours for sildenafil, up to a day or so for tadalafil's aches). If they're consistently unpleasant, don't push through — a lower dose or switching to the other medicine resolves it for most men.
Not normal — seek help
Urgent (same day / emergency)
- An erection lasting more than 2 hours (priapism) — go to A&E. Untreated prolonged erections can permanently damage penile tissue. Don't wait to see if it passes and don't be embarrassed; emergency departments treat this routinely
- Sudden loss or major deterioration of vision in one or both eyes — stop the medicine and seek urgent medical attention (a rare condition called NAION must be ruled out)
- Sudden hearing loss or ringing — rare, but needs same-day assessment
- Chest pain during or after sex — call 999. Critically: tell paramedics you've taken a PDE5 inhibitor, because the standard chest-pain treatment (GTN, a nitrate) is dangerous in combination
- Fainting, severe dizziness, or an allergic reaction (facial swelling, difficulty breathing) — emergency care
The interaction that matters most
Never combine PDE5 inhibitors with nitrates (GTN spray or tablets, isosorbide mononitrate — angina medicines) or recreational poppers (amyl nitrite). Both relax blood vessels by a complementary mechanism, and together they can drop blood pressure to dangerous levels. This is the single most important safety rule with these medicines, and it's why a proper consultation asks about your heart history and medicines.
Reducing side effects in the first place
- Right dose, not max dose — many men do well on lower doses with fewer effects; doses are adjustable in both directions
- Watch alcohol — it amplifies dizziness and headaches and independently worsens erections
- Time meals — heavy fatty food delays sildenafil and can worsen indigestion; tadalafil doesn't care
- Switch if one doesn't suit — visual effects bother you? Try tadalafil. Lingering aches? Try sildenafil. Individual fit is real — see our sildenafil vs tadalafil comparison
Frequently asked questions
How long do sildenafil side effects last?
Usually only while the medicine is active — a few hours. Tadalafil's effects (including muscle aches) can span a day or so, matching its 36-hour window.
Is a 2-hour erection really an emergency?
An erection over 2 hours that isn't subsiding warrants urgent assessment, and over 4 hours is unambiguously an emergency — permanent tissue damage becomes a real risk. Go to A&E rather than waiting it out.
Can I take painkillers for the headache?
Paracetamol is fine alongside PDE5 inhibitors. Persistent or severe headaches on every dose suggest trying a lower dose or the other medicine.
Why can't I use poppers with ED tablets?
Poppers are nitrites — combined with a PDE5 inhibitor they can cause a sudden, dangerous fall in blood pressure. The combination is never safe.
References
- NHS. Sildenafil — side effects. nhs.uk/medicines/sildenafil-viagra.
- NHS. Tadalafil — side effects. nhs.uk/medicines/tadalafil.
- Sildenafil / Tadalafil — Summaries of Product Characteristics. medicines.org.uk.
- European Association of Urology. Guidelines on sexual and reproductive health — priapism management.