Why side effects happen at all
PDE5 is not confined to the penis. It exists in blood vessels throughout the body, in the oesophageal sphincter and in the nasal mucosa. Blocking it dilates vessels elsewhere too — which produces headache, flushing and nasal congestion — and relaxes the sphincter that keeps stomach acid down, producing reflux.
The differences between the drugs come from which related enzymes they also touch. Sildenafil has some activity at PDE6 in the retina, hence the blue tinge. Tadalafil has some activity at PDE11 in skeletal muscle, hence the back ache. Avanafil is the most selective, and correspondingly the least likely to cause either.
The common effects and what to do
| Effect | Roughly how common | What helps |
|---|---|---|
| Headache | About 1 in 6 | Hydrate well; a simple analgesic taken with the dose. Often improves after several uses. If persistent, try a lower dose or a different molecule. |
| Facial flushing | About 1 in 10 | Harmless and usually brief. Avoid alcohol, which compounds it. |
| Nasal congestion | About 1 in 10 | Saline spray. Check with a pharmacist before adding a decongestant if you have high blood pressure. |
| Indigestion or reflux | About 1 in 14 | Avoid lying flat soon after; avoid large fatty meals with the dose; discuss antacids with a pharmacist. |
| Blue tinge or light sensitivity | About 1 in 30 (sildenafil) | Temporary. More common at higher doses. Switching to tadalafil or avanafil usually eliminates it. |
| Back or muscle ache | About 1 in 20 (tadalafil) | Appears 12–24 hours after the dose. Responds to simple analgesia; a lower dose or a different molecule resolves it. |
| Dizziness | Uncommon | Stand up slowly, stay hydrated, moderate alcohol. Review alpha-blocker timing with your prescriber. |
Rare but serious effects
- Priapism
- An erection lasting more than four hours. Rare with tablets, more likely with injection therapy. A surgical emergency — go to an emergency department, do not wait it out.
- NAION
- Non-arteritic anterior ischaemic optic neuropathy — sudden, painless vision loss in one eye. Very rare. Risk appears higher in people with a 'crowded' optic disc, diabetes or hypertension. Anyone with a previous episode should not take these drugs.
- Sudden hearing loss
- Rare, sometimes with tinnitus or dizziness. Stop the medication and seek same-day care.
- Severe hypotension
- Most likely with nitrates (contraindicated), alpha-blockers, or dehydration.
When to switch rather than tolerate
Side effects are not something to endure indefinitely. There are four molecules with meaningfully different profiles, and switching is straightforward.
| If your problem is | Consider |
|---|---|
| Visual disturbance on sildenafil | Tadalafil or avanafil — minimal PDE6 activity |
| Back or muscle ache on tadalafil | Sildenafil or avanafil — no PDE11 activity |
| Persistent headache on any of them | A lower dose first, then a different molecule; avanafil is often best tolerated |
| Reflux | A lower dose, dosing away from meals, or a different molecule |
| Needing an effect too quickly | Avanafil, the fastest to act |
| Disliking the planning | Daily low-dose tadalafil |
Frequently asked questions
Are ED medication side effects dangerous?
Do side effects get better over time?
Why do I get a blue tinge to my vision?
Why does my back hurt after tadalafil?
Can I take painkillers with ED medication?
What this is based on
We link to primary sources — clinical guidelines, regulator publications and peer-reviewed research — wherever possible. Links open on third-party sites we do not control.
- [01]U.S. Food and Drug Administration. Drugs@FDA — approved drug products and prescribing information.
- [02]MedlinePlus (National Library of Medicine). Drugs, Herbs and Supplements.
- [03]American Urological Association. Erectile Dysfunction: AUA Guideline (2018).