PDE5 inhibitors — sildenafil, tadalafil, vardenafil, avanafil — must never be combined with nitrates. That includes:
- Prescribed nitrates for angina: GTN spray or tablets, isosorbide mononitrate, isosorbide dinitrate
- Recreational alkyl nitrites — poppers
This is not a caution or a relative contraindication. It is absolute.
Why It Is Dangerous
Both drug classes lower blood pressure, through complementary parts of the same pathway. Nitrates increase nitric oxide, raising cGMP. PDE5 inhibitors prevent cGMP being broken down.
Together the effect is not additive but amplified: cGMP accumulates, vessels dilate profoundly, and blood pressure can fall to a level that stops adequate blood reaching the heart and brain. The result can be collapse, heart attack, stroke or death.
The Timing Trap
People assume that if the tablet has "worn off", the risk has gone. That is wrong, and it is where tadalafil in particular catches people out.
- Sildenafil, vardenafil, avanafil: the usual advice is to avoid nitrates for at least 24 hours
- Tadalafil: at least 48 hours, because of its long duration
The subjective effect fading is not the same as the drug leaving your system. If you took tadalafil on Friday, Saturday night is still within the window.
Why Poppers Specifically
Poppers are widely used recreationally, are not obtained on prescription, and are not something people think of as medication. So they are frequently not mentioned when someone is asked "are you taking any other medicines?"
They are the most likely nitrate exposure for a man buying ED medication, and the least likely to be disclosed. If a pharmacist or prescriber asks about recreational drug use, this is what the question is for — and an accurate answer costs nothing while an inaccurate one can be fatal.
If You Use Poppers
The safe position is not to combine them at all. If you use poppers and want ED treatment, say so during the consultation. A prescriber can discuss the timing and the risks properly, and there may be alternatives that do not carry this interaction.
What you should not do is obtain ED medication from a source that does not ask, and then work it out yourself.
In an Emergency
If someone becomes unwell after combining them — chest pain, severe dizziness, fainting, confusion — call 999 and say exactly what was taken, including the recreational drug. Emergency treatment for this situation differs from standard care, and the usual first-line drugs for chest pain are nitrates, which would make things dramatically worse.
Nobody in an emergency department will be interested in judging the disclosure. They will be interested in not giving a nitrate to someone who has taken a PDE5 inhibitor.
Other Interactions Worth Knowing
Less dramatic but real:
- Alpha blockers for prostate symptoms or blood pressure can cause a significant drop when combined — usually manageable with timing and dose adjustment, but it needs discussing
- Riociguat and similar drugs for pulmonary hypertension are contraindicated
- Some antifungals, antibiotics and HIV medicines raise PDE5 inhibitor levels, requiring dose adjustment
All of which is the argument for buying from somewhere that asks what else you take, rather than from somewhere that simply takes payment.