Erectile Dysfunction: Causes, Symptoms and Diagnosis
A complete, NICE-aligned guide to erectile dysfunction — covering causes, symptoms, all four MHRA-approved treatments, psychological ED, co-morbidities, and how to get a discreet online prescription.
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Erectile Dysfunction: Causes, Symptoms and Diagnosis
What erectile dysfunction is, why it happens, how it’s diagnosed, what it can say about your wider health, and the treatment options in the UK.
Part of our erectile dysfunction health guides.
Key fact: Erectile dysfunction is common and usually treatable, and because it shares causes with heart disease and diabetes, it can be an early sign of those conditions. A new erection problem is a good reason for a health check.
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Start ED Consultation →What is erectile dysfunction?
Erectile dysfunction (ED) is when you regularly can’t get or keep an erection firm enough for satisfying sex. Most men have occasional difficulties, often linked to tiredness, stress or alcohol, and that’s normal. It becomes ED when it happens persistently, causes you distress, or follows a consistent pattern over several weeks.
ED is the most common sexual problem men see a doctor about, but many men never ask for help because of embarrassment or a belief that nothing can be done. It becomes more common with age, but it can affect men of any age. Most men with ED can be treated successfully.
This guide covers how erections work, what causes ED, how it’s recognised and diagnosed, its links with your wider health, and the full range of treatments. For a shorter overview, see ED: the basics.
How erections work, and why they fail
An erection depends on a chain of events happening in the right order. Sexual stimulation, physical or mental, releases a chemical messenger called nitric oxide in the penis. This relaxes the smooth muscle in the penile arteries, widening them so blood flows into the two spongy chambers of the penis (the corpora cavernosa). As the chambers fill, they press on the veins that drain the penis, and the erection becomes firm.
ED happens when this process is disrupted at any stage: not enough blood flow, damage to the nerves, a hormone imbalance, or psychological factors such as anxiety interrupting the signal. An enzyme called PDE5 normally switches the “relax” signal off. ED tablets (PDE5 inhibitors) block this enzyme, making it easier for an erection to happen and last when you’re aroused.
What causes erectile dysfunction?
ED has three main groups of causes. They often overlap, and many men have more than one.
Physical causes
- Heart and circulation disease: narrowed arteries reduce blood flow to the penis. ED can be an early sign of vascular disease.
- Diabetes: damages both the blood vessels and the nerves that erections depend on.
- High blood pressure: damages artery walls and reduces blood flow.
- Obesity: linked with low testosterone, insulin resistance and poorer blood vessel function.
- Low testosterone (hypogonadism): reduces sex drive and can weaken erections.
- Nerve conditions: multiple sclerosis, Parkinson’s disease, spinal cord injury, and nerve damage after pelvic or prostate surgery.
- Sleep apnoea: linked with lower testosterone and poorer oxygen supply at night.
Psychological causes
- Performance anxiety: a common cause, especially in younger men, and it can become a self-reinforcing cycle.
- Depression and anxiety: interfere with arousal and sex drive.
- Relationship difficulties: communication problems, emotional distance or unresolved conflict.
- Stress: long-term stress affects hormones and sexual function.
Medicines that can cause ED
- Antidepressants, particularly SSRIs
- Beta-blockers and some other blood pressure medicines
- Thiazide diuretics (water tablets)
- Anti-androgens and some prostate medicines
- Opioid painkillers
Don’t stop a prescribed medicine without talking to your doctor first. For a full breakdown, see what causes erectile dysfunction, psychological erectile dysfunction and ED in young men.
Symptoms and diagnosis
The main symptom of ED is persistent difficulty getting or keeping an erection firm enough for satisfying sex, usually over at least several weeks. Some men also notice lower sex drive, fewer or no erections on waking, or problems with ejaculation, such as ejaculating too early or too late.
Clues to the cause
- Consistent difficulty, not just now and then.
- No erections on waking or at night: suggests a physical cause. If you still get them, a psychological cause is more likely.
- Situational pattern: ED in some situations but not others suggests a psychological factor.
- Sudden onset, especially after a stressful event, suggests a psychological cause; a gradual onset suggests a physical one.
- Heart and circulation risk factors: high blood pressure, diabetes, being overweight or smoking.
How ED is assessed
A full assessment includes your blood pressure, blood sugar (HbA1c or a fasting glucose test), cholesterol, a morning testosterone level, thyroid function if needed, and questions about your mood and relationships. Access Doctor’s online consultation covers your medical history as part of the prescribing assessment; blood tests are done by your GP.
See a GP in person if you’re under 40 with no obvious cause, if your ED started alongside chest pain or other heart symptoms, or if blood tests show significantly abnormal results. This is best done before, or alongside, any online treatment.
For more detail, see signs of erectile dysfunction.
Erectile dysfunction and your wider health
ED is rarely just about sex. It is closely linked with heart disease, diabetes, obesity, depression and hormone problems, and it can be an early warning sign of them. That’s why a check of your wider health is part of good care for ED.
ED and heart disease
The arteries in the penis are smaller than those in the heart, so narrowing can affect erections before it causes heart symptoms, often by several years. Studies link ED with a higher risk of heart attack and stroke, so new ED in a man with risk factors needs a heart health check. Read the guide
ED and diabetes
ED is much more common in men with diabetes, because diabetes damages blood vessels and nerves and can lower testosterone. ED tablets still help many men with diabetes, though they may work less well, and good blood sugar control helps. Read the guide
Psychological ED
Performance anxiety, depression, stress and relationship difficulties are common causes, especially in younger men, and the worry about failing can keep the problem going. Talking therapies such as CBT and psychosexual therapy can help. Read the guide
ED after surgery
Operations on the prostate, bladder, bowel or pelvic blood vessels can damage the nerves or blood supply involved in erections. Recovery and treatment options depend on the operation. Read the guide
How erectile dysfunction is treated
NICE recommends a PDE5 inhibitor tablet as the first medicine to try for most men with ED, alongside treating any underlying cause and making lifestyle changes. Four are licensed in the UK. They all work in the same way, and sexual arousal is always needed: none of them causes an erection on its own.
| Medicine | When to take it | How long it lasts | Good to know | Guide |
|---|---|---|---|---|
| Sildenafil (Viagra) | About 1 hour before sex | About 4 to 5 hours | A heavy or high-fat meal can slow it down. Viagra Connect 50mg can be bought from a pharmacy after a pharmacist consultation. | Sildenafil uses |
| Tadalafil (Cialis) | At least 30 minutes before sex, or a low dose every day | Up to 36 hours | Not affected by food. The 5mg daily dose is also licensed for an enlarged prostate. | Tadalafil uses |
| Vardenafil (Levitra) | 25 to 60 minutes before sex | About 4 to 5 hours | A high-fat meal can slow it down. Not suitable with some heart rhythm medicines, or for people with a heart rhythm problem called long QT. | Vardenafil guide |
| Avanafil (Spedra) | 15 to 30 minutes before sex | Up to about 6 hours | The quickest to start working. Available as the brand Spedra. | Avanafil guide |
For a side-by-side comparison, see Viagra vs Cialis vs Levitra vs Spedra and tadalafil vs sildenafil.
If tablets don’t work or aren’t suitable
- Alprostadil: a medicine given as an injection into the penis, a pellet placed in the urethra, or a cream applied to the tip of the penis. It works even when the nitric oxide signal is weak, so it can help where tablets don’t or can’t be used.
- Aviptadil with phentolamine: another injection into the penis, used by specialists.
- Vacuum erection devices: a pump that draws blood into the penis, with a ring to hold the erection. No medicine is involved.
- Talking therapies: CBT and psychosexual therapy help when anxiety, stress or relationship issues play a part, often alongside tablets at first.
- Testosterone treatment: only if blood tests confirm low testosterone. It can improve sex drive and help tablets work better.
- Penile implants: a surgical option when other treatments haven’t worked.
Lifestyle changes
For many men, healthier habits improve erections and help tablets work better, and for some they’re enough on their own. See lifestyle changes for erectile dysfunction.
- Lose weight if you’re overweight: this improves blood vessel and hormone function.
- Be active: regular aerobic exercise helps erections, especially in men with heart and circulation risk factors.
- Stop smoking: smoking narrows arteries; stopping improves blood flow over time.
- Cut down on alcohol: heavy drinking makes erections harder to get, both on the night and in the long term.
Our guide to whether ED treatment works explains what to expect and what to do if first treatments don’t help. To compare ED tablets and prices, see our ED treatment online page.
Safety: medicines that must never be combined
Never take an ED tablet with: nitrate medicines such as a GTN spray or patch, or isosorbide mononitrate or dinitrate tablets (for angina); nicorandil; riociguat; or nitrate “poppers” (amyl or butyl nitrite). Together they can cause a sudden, dangerous fall in blood pressure. If you use any of these, talk to your doctor about other options. Access Doctor’s consultation checks for all of them.
ED tablets also aren’t suitable if you’ve recently had a heart attack or stroke, or have unstable angina, certain types of heart failure, or very low or uncontrolled high blood pressure. Get urgent medical help if you have chest pain after taking an ED tablet, sudden loss of sight or hearing, or an erection that is painful or lasts more than 2 hours.
For the full list of interactions, see sildenafil uses, side effects and interactions and Cialis drug interactions.
Common myths about erectile dysfunction
Myth: ED only affects older men
False. ED becomes more common with age, but it can affect men of any age. One study found that about 1 in 4 men seeking help for new erection problems were aged 40 or under. In younger men, stress and performance anxiety are common causes, but physical causes should still be checked. See ED in young men.
Myth: ED means you’re not attracted to your partner
False. ED usually has physical causes, such as reduced blood flow, nerve or hormone problems, or side effects of medicines, and it is not a reflection of attraction or desire. When psychological factors are involved, they’re usually stress or anxiety rather than lack of attraction.
Myth: ED tablets cause an erection on their own
False. ED tablets make it easier to get and keep an erection when you’re sexually aroused. Without arousal, nothing happens. See what is Viagra?
Myth: ED medication is dangerous for the heart
For most men whose heart health is stable, ED tablets are safe when prescribed after a medical assessment. They must never be taken with nitrate medicines (such as a GTN spray), nicorandil, riociguat or “poppers”, and they are not suitable if you have recently had a heart attack or stroke, have unstable angina or certain types of heart failure, or very low or uncontrolled high blood pressure. Your prescriber checks for all of these during the consultation. See ED and heart disease.
Myth: Online ED medication isn’t safe or legitimate
Legitimate UK online pharmacies are registered with the General Pharmaceutical Council (GPhC), and a pharmacist reviews your medical history before anything is supplied. Access Doctor’s pharmacy, Pharmadocs UK Limited, is GPhC-registered (No. 9011198), and our prescriptions are issued by GPhC-registered pharmacist prescribers. The real risk comes from websites that sell ED tablets without a consultation, which can contain the wrong dose or ingredient. Always check a pharmacy’s GPhC registration.
All erectile dysfunction guides
Our full library of ED guides, medically authored and reviewed by Dr Abdishakur M Ali (GMC no. 7041056).
Understanding ED
- ED: the basics: what ED is, how erections work and when to seek help
- What causes erectile dysfunction?: physical, psychological and medicine-related causes
- Signs of erectile dysfunction: symptoms, blood tests and next steps
- Erectile dysfunction in young men: why it happens and how it’s treated
- Psychological erectile dysfunction: the anxiety cycle, CBT and sex therapy
- Can surgery cause erectile dysfunction?: ED after prostate, pelvic and vascular surgery
ED and health conditions
Treatment and lifestyle
- Understanding and overcoming erectile dysfunction: every treatment option explained
- Lifestyle changes for erectile dysfunction
- Does erectile dysfunction treatment work?
- Stopping ED medication: what happens and when it makes sense
- Kamagra dangers: why it’s unsafe and what to use instead
Comparing ED tablets
Sildenafil (Viagra)
- What is Viagra?
- Sildenafil uses: dosage, side effects and interactions
- Taking Viagra for the first time
Tadalafil (Cialis)
- Tadalafil uses: on-demand and daily dosing
- Daily tadalafil: the 5mg daily dose explained
- Cialis drug interactions: medicines, alcohol and recreational drugs
Vardenafil (Levitra) and avanafil (Spedra)
Frequently asked questions about erectile dysfunction
What is erectile dysfunction?
Erectile dysfunction is when you regularly can't get or keep an erection firm enough for satisfying sex. Occasional difficulties are normal. ED is a concern when it happens regularly, causes distress, or follows a consistent pattern over several weeks. It becomes more common with age, but it can affect men of any age.
What are the most common causes of erectile dysfunction?
The most common physical causes are heart and circulation disease, diabetes, high blood pressure, obesity and low testosterone. Psychological causes, particularly performance anxiety, depression and stress, are common in younger men. Some medicines, such as antidepressants, beta-blockers and diuretics, can also cause ED. Many men have a mix of physical and psychological factors.
What is the difference between sildenafil and tadalafil?
Sildenafil (Viagra) is taken about an hour before sex and lasts about 4 to 5 hours; a heavy meal can slow it down. Tadalafil (Cialis) is taken at least 30 minutes before sex, lasts up to 36 hours and isn't affected by food, and it can also be taken as a low daily dose. They work about as well as each other for most men, so the choice usually comes down to how you want to use it.
Can erectile dysfunction be a sign of heart disease?
Yes. ED and heart disease often share the same cause: narrowed arteries. Because the arteries in the penis are smaller than those in the heart, narrowing can affect erections first, often several years before any heart symptoms. New ED in a man with risk factors such as high blood pressure, diabetes or smoking is a good reason for a heart health check.
Is erectile dysfunction more common in diabetic men?
Yes. ED is much more common in men with diabetes, because diabetes can damage the blood vessels and nerves needed for an erection and can lower testosterone. Good blood sugar control helps, and ED tablets still work for many men with diabetes. Diabetes is one of the conditions for which the NHS allows ED medicines to be prescribed.
Can psychological causes lead to erectile dysfunction?
Yes. Performance anxiety, depression, stress and relationship difficulties are common causes, especially in younger men. One difficult experience can lead to worry, the worry makes an erection harder, and each difficulty adds to the anxiety. Clues include still having erections on waking, ED only in some situations, and a sudden start. CBT and psychosexual therapy can help, sometimes alongside ED tablets at first.
What treatments are available for erectile dysfunction in the UK?
NICE recommends a PDE5 inhibitor tablet first: sildenafil, tadalafil, vardenafil or avanafil. If tablets don't work or aren't suitable, options include alprostadil (an injection, urethral pellet or cream), a vacuum erection device, talking therapies, testosterone treatment if levels are low, and, rarely, a penile implant. Lifestyle changes such as losing weight, being active and stopping smoking also help.
What medicines, drinks or drugs should be avoided with Cialis?
Cialis (tadalafil) must never be combined with nitrate medicines such as GTN spray or isosorbide mononitrate, with nicorandil or riociguat, or with nitrate-based recreational drugs known as poppers, because the combination can cause a dangerous fall in blood pressure. Alpha-blockers such as tamsulosin need caution and careful timing rather than an outright ban. Moderate alcohol is generally lower risk than with some other ED medicines, while heavy drinking increases dizziness and can make erections harder to achieve. Stimulant drugs including cocaine, MDMA and methamphetamine are not advised alongside tadalafil because of the added strain on the heart.
Is it safe to take ED medication long-term?
For most men, yes. Sildenafil has been used since 1998, and there's no evidence that ED tablets become less effective over time or cause addiction at prescribed doses. Long-term use is normal for men with ongoing physical causes. It's still worth having your health and medicines reviewed regularly, especially if you start any new medicine.
Is ED treatment available on the NHS?
Generic sildenafil can be prescribed on the NHS for any man with ED. Some other ED medicines can only be prescribed on the NHS for men who meet set criteria, such as diabetes, multiple sclerosis, Parkinson's disease, prostate cancer treatment, kidney failure treated with dialysis, spinal cord injury, or severe distress assessed by a specialist. You can also get a private prescription online without a GP appointment.
Is Kamagra safe to use?
No. Kamagra is not licensed in the UK and is illegal to sell here. Products sold as Kamagra come from unlicensed manufacturers, so the ingredient, dose and purity can't be guaranteed. Only buy ED medication from a pharmacy you can find on the General Pharmaceutical Council (GPhC) register.
How do I get ED treatment from Access Doctor?
Complete a short, confidential online consultation. A GPhC-registered pharmacist independent prescriber reviews your answers and, if treatment is suitable, issues a prescription. No GP appointment is needed. Orders approved before 3pm, Monday to Friday, are dispatched the same day in plain packaging by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day. GPhC pharmacy registration #9011198.
Ready to talk about ED treatment?
It takes about 5 minutes. A GPhC-registered pharmacist prescriber reviews your answers and, if treatment is suitable, we dispatch it from our UK pharmacy in plain packaging.
Start ED Consultation →References
- NICE Clinical Knowledge Summaries. Erectile dysfunction. cks.nice.org.uk/topics/erectile-dysfunction
- NHS. Erection problems (erectile dysfunction). nhs.uk
- European Association of Urology. Guidelines on Sexual and Reproductive Health, 2024. uroweb.org
- Dong JY, Zhang YH, Qin LQ. Erectile dysfunction and risk of cardiovascular disease: meta-analysis of prospective cohort studies. J Am Coll Cardiol 2011;58:1378–85. PubMed
- Capogrosso P et al. One patient out of four with newly diagnosed erectile dysfunction is a young man. J Sex Med 2013;10:1833–41. Abstract
- Summaries of product characteristics for sildenafil, tadalafil, vardenafil and avanafil. medicines.org.uk/emc
- General Pharmaceutical Council. Register of pharmacies. pharmacyregulation.org
Medical disclaimer: This page is for information only and isn't a substitute for medical advice. Most ED medicines are prescription-only, so a clinical consultation is needed before they can be supplied. Always follow your prescriber's advice. In a medical emergency, call 999.
