Sildenafil, Tadalafil and Other Medicines: Which Interactions Actually Matter
Reviewed by the Kamagra AUS Pharmacy Team on 12 November 2025 · Next review June 2027
Summary
PDE5 inhibitors like sildenafil and tadalafil have one interaction that's an absolute no — and a handful of others worth mentioning to your doctor. Here's the real picture, without the noise.
On this page
PDE5 inhibitors — the drug class that includes sildenafil, tadalafil, vardenafil and avanafil — have one interaction that overrides every other consideration, and a smaller list of medicines worth mentioning to a doctor or pharmacist before starting treatment. Sorting the absolute rule from the "worth a conversation" list makes the whole topic far less confusing than it can look online.
The one absolute rule: nitrates
PDE5 inhibitors must never be combined with nitrate medicines (commonly prescribed for angina, such as glyceryl trinitrate) or with amyl nitrite and related recreational "poppers." Both nitrates and PDE5 inhibitors relax blood vessels, and together they can drop blood pressure to a dangerous level. This is the one interaction that is a hard stop, not a "check with your doctor" — if you take a nitrate medicine for a heart condition, PDE5 inhibitors are not a safe option without specific medical guidance.
Blood pressure medicines, generally
Many men on treatment for high blood pressure take a PDE5 inhibitor without issue, since doctors prescribe them together regularly — but the combination can occasionally cause a bigger-than-expected drop in blood pressure in some individuals, particularly when a new blood pressure medicine or dose is started around the same time. Mentioning any blood pressure medicine to your doctor or pharmacist before starting a PDE5 inhibitor is sensible, not because it's usually a problem, but because your prescriber can flag it if your specific combination needs a closer look.
Alpha-blockers (for prostate symptoms)
Alpha-blockers, sometimes prescribed for an enlarged prostate, work similarly to lower blood pressure and can compound with a PDE5 inhibitor's effect on blood pressure. Doctors often manage this by adjusting timing or dose rather than ruling either medicine out — it's a "discuss with your prescriber" situation, not an automatic no.
Blood thinners and other regular medicines
There's no broad, well-established direct interaction between PDE5 inhibitors and common blood-thinning medicines such as aspirin or warfarin, and many men take both. That said, "no well-established interaction" isn't the same as "never mention it" — any regular prescription medicine, blood thinners included, is worth disclosing to your doctor or pharmacist when starting a new one, simply so the full picture is on record.
The practical takeaway
The single rule that matters most is nitrates: never combine them with sildenafil, tadalafil, vardenafil or avanafil. Everything else on this list is a "worth mentioning," not a "definitely avoid" — and the safest way to get a definitive answer for your own situation is a short conversation with a doctor or pharmacist who can see your full medicine list.
This article is general information, not medical advice. It does not cover every possible interaction. Always tell your doctor or pharmacist about every medicine, supplement and recreational substance you use before starting a new medicine.
Frequently asked questions
What's the one medicine I should never combine with sildenafil or tadalafil?+
Nitrate medicines (such as glyceryl trinitrate for angina) and amyl nitrite ('poppers'). The combination can cause a dangerous drop in blood pressure and is not a case-by-case judgement call — it's an absolute rule.
Can I take a PDE5 inhibitor if I'm on blood pressure medicine?+
Often yes, and doctors commonly prescribe both together, but it's worth mentioning your blood pressure medicine to your doctor or pharmacist first, since the combined effect on blood pressure can vary between individuals.
Do PDE5 inhibitors interact with blood thinners like aspirin or warfarin?+
There's no well-established direct interaction, and many men take both. Still, disclose every regular medicine, including blood thinners, to your doctor or pharmacist before starting a PDE5 inhibitor.
I take an alpha-blocker for prostate symptoms — can I also take sildenafil?+
Possibly, but this combination is one your prescriber typically manages through timing or dose, since both medicines can lower blood pressure. Speak with your doctor before combining them.
Kamagra AUS Health Editorial Team
Plain-English health writing from our in-house editorial team — sourced to the TGA, healthdirect and each medicine's product information, and focused on how Australians actually access and use medicines safely.
How our content is written & reviewedSources for the medical information in this guide
- Healthdirect Australia — Sildenafil — Australian guidance on medicines and health conditions — search "sildenafil" for current advice.
- PDE5 Inhibitors — StatPearls, NCBI Bookshelf — Peer-reviewed clinical pharmacology of the whole drug class.
- TGA — Sildenafil product information — Therapeutic Goods Administration — search the TGA's Product Information / ARTG for sildenafil-based products.
Related treatments
Browse the medicines and conditions related to this guide:
Mentioned in this guide
Shop the treatments covered here
Genuine medicines from the guide above — discreetly delivered Australia-wide.
