Urology / Men's health
PDE5 inhibitors
Erectile dysfunction tablets (e.g. sildenafil, tadalafil) — The first-line tablets for erectile dysfunction — effective and safe, but never combined with nitrates.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
Quick answer
What is PDE5 inhibitors?
PDE5 inhibitors are tablets that treat erectile dysfunction by improving blood flow into the penis in response to sexual stimulation. Some are also used for benign prostate symptoms and a rare lung-pressure condition.
- How it works: During arousal the body releases nitric oxide, which raises a signalling molecule (cyclic GMP) that relaxes blood vessels and lets the penis fill with blood.
- In practice: In practice PDE5 inhibitors are the first-line treatment for erectile dysfunction, and most respond well.
What it is
PDE5 inhibitors are tablets that treat erectile dysfunction by improving blood flow into the penis in response to sexual stimulation. Some are also used for benign prostate symptoms and a rare lung-pressure condition. They are the usual first-choice treatment.
How it works
During arousal the body releases nitric oxide, which raises a signalling molecule (cyclic GMP) that relaxes blood vessels and lets the penis fill with blood. PDE5 inhibitors block the enzyme that breaks cyclic GMP down, so the natural erection response is stronger and lasts longer. Because the same pathway is shared with nitrate heart drugs, combining the two removes the body's "brake" on blood-vessel widening — which is why that combination is dangerous.
In practice
In practice PDE5 inhibitors are the first-line treatment for erectile dysfunction, and most respond well. The single most important safety rule overshadows everything else: they must never be taken with nitrates (such as GTN spray or isosorbide tablets used for angina) or with nicorandil, because the combination can cause a dangerous, sometimes fatal, drop in blood pressure — anyone using these heart medicines cannot use PDE5 inhibitors. They are also used with great caution alongside alpha-blockers (often prescribed for prostate symptoms) and other blood-pressure-lowering drugs, separating doses to avoid dizziness or fainting. A practical point that affects how well they work: the shorter-acting agents need sexual stimulation to work and, for some, are best taken on an emptier stomach, while longer-acting tadalafil gives a wider window and is also used in a small daily dose for prostate symptoms. Erectile dysfunction can be the first sign of cardiovascular disease, so it is also a prompt to check heart and metabolic health. Men should seek urgent help for an erection lasting over four hours or sudden visual or hearing changes.
Examples
Practical use
How to take it & use it well
- Take the tablet a while before you plan to be intimate, as most of these medicines need time to start working. They only help when you are also sexually aroused, so they do not cause an erection on their own.
- Some of these tablets work better on an empty stomach, as a large or fatty meal can slow them down, while a longer-acting option can be taken either as needed or as a small regular dose. Follow the advice for the specific one you have been given.
- Limit alcohol around the time you take it, as drinking can both reduce how well it works and add to side effects such as a drop in blood pressure or dizziness.
- Do not take more than one of these tablets, or repeat a dose sooner than advised, as taking extra does not improve the effect and increases the risk of side effects.
- If the first occasion does not work, do not assume the medicine has failed. It often takes several proper attempts, with arousal, before you and your doctor can judge whether it suits you.
- Seek urgent help for an erection that is painful or lasts several hours, or for sudden chest pain, loss of vision or hearing while using it, as these are emergencies.
Common uses
- Erectile dysfunction
- Benign prostatic symptoms (daily tadalafil)
- Pulmonary arterial hypertension (specific products, specialist)
Monitoring
- Response and tolerability; cardiovascular fitness for sexual activity
- Blood pressure and interacting medicines (nitrates, alpha-blockers)
- Underlying causes of ED (diabetes, vascular, hormonal, psychological)
Weighing it up
Advantages & disadvantages
Advantages
- They are an effective and well-established treatment for erectile difficulties and help many men regain reliable erections.
- They are taken by mouth and discreet, with options that work on demand or, for one of them, as a small daily dose.
- One of the longer-acting choices can also help with symptoms of an enlarged prostate at the same time.
- They work with natural arousal rather than forcing an erection, so the experience feels more normal.
- They are generally well tolerated, and side effects are often mild and short-lived.
Disadvantages
- They must never be combined with nitrate heart medicines or nicorandil, as together they can cause a dangerous and even fatal fall in blood pressure.
- Common side effects include headache, facial flushing, a blocked nose, indigestion and, with some, temporary changes in vision.
- They do not treat the underlying cause of erection problems, which can include heart disease, diabetes, stress or relationship issues.
- They are not suitable for some men, including those with certain heart conditions or who have recently had a stroke or heart attack.
- Buying them from unregulated websites risks fake products and missing important safety checks of your heart health.
Key safety principles
What to watch for
- NEVER take with nitrates (GTN, isosorbide) or nicorandil — the combination can cause a dangerous, even fatal, fall in blood pressure.
- Use with caution with alpha-blockers and other blood-pressure-lowering drugs (risk of dizziness/fainting); separate dosing as advised.
- Seek urgent help for an erection lasting more than 4 hours (priapism) or sudden loss of vision or hearing.
Key interactions
What to avoid or check alongside
- They must never be taken with nitrate medicines for angina or with nicorandil, as the combination can cause a life-threatening drop in blood pressure.
- Other medicines for the prostate or blood pressure that relax blood vessels, such as alpha-blockers, can add to the blood-pressure-lowering effect and cause dizziness or fainting.
- Certain antibiotics, antifungals and HIV medicines slow how these tablets are broken down, raising their levels and the chance of side effects.
- Other treatments that widen blood vessels, including some recreational drugs known as poppers, can dangerously lower blood pressure when combined.
- Grapefruit juice can increase the amount in your system, so it is best avoided around the time you take it.
Patient & carer advice
- Do not use if you take nitrate or nicorandil heart medicines — tell every prescriber you use these tablets
- The shorter-acting ones need sexual stimulation to work and may work better not straight after a heavy, fatty meal
- Get urgent help for an erection lasting over 4 hours or any sudden vision or hearing change
Use with
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Answers
PDE5 inhibitors: frequently asked questions
Why can I never take these tablets with nitrates?
Nitrates and nicorandil, used for angina, and these erection tablets both lower blood pressure. Taken together they can cause a sudden, severe and potentially fatal drop, so this combination is completely off-limits. Always tell your doctor about any heart medicines you take.
How long before sex should I take it?
Most of these tablets need to be taken a while before intimacy to give them time to work, and you still need to feel aroused for them to have an effect. The exact timing differs between the medicines, so follow the advice for the one you have been given.
What should I do if I get an erection that won't go away?
An erection that is painful or lasts for several hours needs urgent medical attention, as it can damage the penis if not treated. Go to A&E rather than waiting for it to settle on its own.
Do these tablets work straight away the first time?
Not always. It can take several proper attempts, with genuine arousal, before you can judge whether the medicine suits you. If repeated tries do not help, go back to your doctor rather than giving up.
Is it safe to buy erection tablets online?
Buying from unregulated websites risks counterfeit medicines and means your heart health is not checked first, which can be dangerous. Get them through your GP, a registered online service or a pharmacist so you are assessed properly.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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