Sildenafil 20mg: Why It Is Not an ED Dose in the UK
Sildenafil 20mg is the Revatio strength for lung disease, not a licensed ED dose. Here is what to take instead, when it works, and what to do if a dose goes wrong.
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Key Takeaways
Sildenafil 20mg is the Revatio dose for lung disease, not a licensed ED dose. ED tablets are 25, 50 and 100mg. They work in 30 to 60 minutes, last about 4 hours, and you should take no more than one dose a day.
Sildenafil 20mg is not licensed for erectile dysfunction (ED) in the UK. It is the strength of Revatio, a prescription-only medicine for pulmonary arterial hypertension (high blood pressure in the lungs), taken three times a day. Generic 20mg sildenafil tablets for this condition also exist. A specialist prescribes them for people with that diagnosis.
Do not use Revatio or other 20mg sildenafil tablets for ED. They were prescribed for a specific lung condition, not for erection problems, and they should not be used for ED, whether they are yours or someone else's.
Why 20mg is unlicensed for ED#
ED tablets come as 25mg, 50mg and 100mg. Viagra and generic sildenafil are sold in these strengths. Generic sildenafil is prescription-only. Viagra Connect (50mg) is the version a pharmacist can supply without a prescription after a consultation.
Most men start on 50mg. The prescriber then moves up to 100mg or down to 25mg depending on results and side effects. The maximum is 100mg, and you should take only one dose in 24 hours.
Some people ask about taking five 20mg Revatio tablets to make 100mg. Do not do this. Matching the milligrams does not make it safe or appropriate. A prescriber checks your heart, kidneys, blood pressure and other medicines before supplying sildenafil for ED, and taking tablets prescribed for someone else, or for another condition, skips those checks. You also cannot make 25mg or 50mg from 20mg tablets. The sums do not work.
If you have been prescribed Revatio, take it only as directed for your lung condition. Speak to your specialist or prescriber if you have ED.
What to expect after taking an ED dose#
| Time after the tablet | What to expect |
|---|---|
| 0 to 30 minutes | Usually nothing yet |
| 30 to 60 minutes | Effect starts for most men, but only with sexual arousal |
| About 1 hour | Levels in the blood peak |
| Up to 4 hours | Erections are easier to get and keep. Some men notice effects for up to 5 hours |
| 24 hours | The earliest time you can take another dose |
For more on timing, see how long sildenafil takes to work.
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What changes the timeline#
- Food. A high-fat meal can delay the effect by about an hour. A light meal makes little difference.
- Alcohol. It can make erections harder to get and add to dizziness. Keep it low.
- Arousal. Sildenafil does not cause an erection by itself. You still need to be aroused.
- Dose. Higher doses have a stronger effect but more side effects. A higher dose does not work faster.
- Stress and worry. Performance anxiety can cancel out a correct dose.
- Your health and medicines. Liver and kidney problems, and some medicines, slow how fast your body clears sildenafil.
If a dose is late, missed or does not work#
Sildenafil is taken as needed, so there is no schedule to miss. If you took it too early or too late, wait. Do not take a second tablet to catch up.
If nothing happens after an hour, do not take another one. Try again another day, leaving at least 24 hours between doses.
One attempt is not a fair test. Try a dose a few times, with a light meal, little alcohol and proper arousal. If it still does not work, ask your prescriber about a different dose or another medicine such as tadalafil.
If you take Revatio for lung disease, take a missed dose as soon as you remember. Then carry on as normal. Never double up.
Who needs a different dose, or should avoid it#
Do not take sildenafil if you:
- use nitrates (such as GTN spray or isosorbide) or nicorandil
- take riociguat
- have severe liver disease, such as cirrhosis
- have had a recent heart attack or stroke
- have very low blood pressure
- have retinitis pigmentosa, or lost sight in one eye from an optic nerve problem
The nitrate risk is serious. See sildenafil and nitrates.
A prescriber may suggest 25mg if you have mild-to-moderate liver impairment or severe kidney impairment (creatinine clearance below 30 mL/min). They may also start at 25mg if you take erythromycin, ketoconazole, itraconazole or saquinavir. These raise sildenafil levels.
Ritonavir and other HIV protease inhibitors have a stricter rule. You should have no more than 25mg in 48 hours.
Tell the prescriber about alpha-blockers, other blood pressure medicines and heart disease. You also need to be fit enough for sex.
Got questions? Speak to a pharmacist on WhatsApp now
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Side effects and warning signs#
Headache is very common (more than 1 in 10 people). Flushing, indigestion, a blocked nose, dizziness and vision changes, such as a blue tint, are common (up to 1 in 10 people). These are more likely at higher doses. For the 100mg dose, see sildenafil 100mg.
Get urgent medical help if you have any of these:
- an erection lasting more than 4 hours
- sudden loss of vision in one eye
- sudden hearing loss or ringing in the ears
- chest pain during sex
Getting the right strength in the UK#
Your GP can prescribe sildenafil for ED. On the NHS, free supply is limited to certain groups, such as men with diabetes, prostate surgery, spinal cord injury, multiple sclerosis or Parkinson's. Others can use a private prescription or Viagra Connect.
ED can sometimes be an early sign of heart or blood vessel disease. A proper assessment matters.
If you buy online, check the pharmacy is on the GPhC register. Avoid any site that sells without asking about your health. Counterfeit tablets are common.
Totiva stocks sildenafil in 50mg and 100mg, and the live service page shows current strengths. Four tablets cost £6.99 (50mg) or £7.99 (100mg). The consultation is free and you only pay once treatment is approved, so you can start an ED consultation when you are ready.
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Medical Information: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting, stopping, or changing any treatment.
