--- title: "Sildenafil and tadalafil: Uses & Side Effects" description: "PDE5 inhibitors for erectile dysfunction — Viagra (sildenafil) and Cialis (tadalafil): how they work, dosing, NHS access, side effects, and safety with…" url: https://healthanswers.co.uk/treatments/sildenafil-and-tadalafil/ robots: noindex --- # Sildenafil and tadalafil: Uses & Side Effects Treatments PDE5 inhibitors for erectile dysfunction — Viagra (sildenafil) and Cialis (tadalafil): how they work, dosing, NHS access, side effects, and safety with heart medicines. Written by HealthAnswers editorial team Medically reviewed by [HealthAnswers UK doctor review panel](https://healthanswers.co.uk/our-doctors/) Reviewed 3 July 2026 ## Quick answer What are sildenafil and tadalafil used for? Sildenafil (Viagra) and tadalafil (Cialis) improve erections by increasing blood flow when you are sexually aroused — they work for about 70 to 80% of men with physical ED. Sildenafil lasts 4 to 6 hours; tadalafil up to 36 hours or can be taken daily at low dose. Available on NHS prescription and from UK pharmacies. Never take with nitrates (GTN spray) or poppers. ## Who is this page for? This page is for people in the UK who want a plain-English overview of Sildenafil and tadalafil, including when to seek help and what NHS care usually involves. It explains general information, not what is wrong with you personally. ## Who should skip this page? Skip this page if you need a diagnosis, a prescription, or emergency care. It cannot replace a GP, pharmacist, NHS 111 or 999. If you are in immediate danger, call 999; for urgent advice that is not life-threatening, call 111 in England, Scotland or Wales, or use your GP out-of-hours service in Northern Ireland. On this page 13 sections ## Key facts about sildenafil and tadalafil - PDE5 inhibitors require sexual stimulation — they do not cause automatic erections. - Generic sildenafil is available on NHS prescription after GP assessment. - Sildenafil works best on an empty stomach; tadalafil is less affected by food. - Combining with nitrates or poppers causes dangerous blood pressure drop — never mix. - See a GP for new ED — it can indicate cardiovascular disease needing treatment. ## PDE5 inhibitors — sildenafil and tadalafil **Sildenafil** (Viagra) and **tadalafil** (Cialis) are **PDE5 inhibitors** — the first-line **medical treatment** for [erectile dysfunction](https://healthanswers.co.uk/conditions/erectile-dysfunction/) with a physical component. They increase blood flow to the penis **when you are sexually aroused** — they do not create desire or spontaneous erections without stimulation. ## How they work During arousal, nerves release **nitric oxide**, raising **cGMP**, which relaxes smooth muscle in penile arteries. **PDE5** breaks down cGMP — inhibitors **prolong** the signal, improving rigidity and maintenance. **Require intact nerve pathways and arousal** — will not work if testosterone is severely low (until corrected) or if purely psychogenic without any arousal. ## Sildenafil (Viagra, generic) | Aspect | Detail | | --- | --- | | Doses | 25, 50, 100mg | | Onset | 30 to 60 minutes | | Duration | 4 to 6 hours | | Food | High-fat meal delays absorption — take on empty stomach for fastest effect | | Frequency | Max once per 24 hours | | NHS | Generic sildenafil on prescription — quantity limits vary by ICB | **Viagra Connect:** 50mg **pharmacy-only** — pharmacist consultation — no prescription needed for eligible men. ## Tadalafil (Cialis, generic) | Aspect | Detail | | --- | --- | | On-demand doses | 10, 20mg | | Daily doses | 2.5, 5mg | | Onset | 30 minutes (daily dosing removes timing pressure) | | Duration | Up to 36 hours (“weekend pill”) | | Food | Minimal interaction | | Daily 5mg | Also licensed for benign prostatic hyperplasia (BPH) urinary symptoms | **Advantage:** Less planning; daily low dose suits frequent activity or combined ED/BPH. ## Effectiveness **70 to 80%** of men with physical ED achieve improved erections sufficient for intercourse. **Less effective when:** - diabetes with neuropathy - post- radical prostatectomy (nerve damage) - severe vascular disease - low testosterone untreated **Try alternate PDE5 inhibitor** if first fails — non-responders to sildenafil sometimes respond to tadalafil. ## Getting them in the UK - GP prescription — after ED assessment and cardiovascular review - Pharmacy supply — Viagra Connect, some tadalafil brands — pharmacist checklist - Private online clinics — must be regulated — check GPhC registration **Avoid:** unregulated websites selling counterfeit tablets — may contain wrong dose or contaminants. ## Side effects **Common:** - headache - flushing - dyspepsia - nasal congestion - back pain (tadalafil more than sildenafil) - limb pain (tadalafil) **Visual:** blue tinge, light sensitivity — rare; **sudden vision loss** (NAION) — extremely rare — stop and seek help **Hearing loss** — rare — reported ## Critical safety — nitrates and poppers **Absolute contraindication:** - GTN spray/tablets (angina) - Isosorbide mononitrate/dinitrate - Recreational poppers (amyl nitrite) Combined effect causes **profound hypotension** — potentially **fatal**. If you have angina, discuss with cardiologist — ED treatment may still be possible with alternative angina management in stable disease. ## Other interactions and cautions - Alpha-blockers (tamsulosin, doxazosin) — hypotension risk — separate dosing times; start PDE5 inhibitor at lowest dose - CYP3A4 inhibitors (ketoconazole, erythromycin) — increase PDE5 levels — lower dose sildenafil - Recent stroke or MI — usually defer 6 months - Unstable angina, severe heart failure — avoid - Retinitis pigmentosa — contraindicated - Anatomical deformity (Peyronie’s severe) — caution ## Priapism — emergency Erection **lasting over 4 hours** without sexual stimulation — **phone 999 or attend A&E** — tissue damage and permanent ED risk if untreated. ## Cost comparison **Generic sildenafil** — cheapest NHS option — pennies per tablet. **Tadalafil daily** — higher cost but convenience premium. **Branded Viagra/Cialis** — same drug, higher price — no clinical advantage over generic. ## Lifestyle alongside tablets PDE5 inhibitors work best combined with: - smoking cessation - weight loss - blood pressure, diabetes, cholesterol control - reduced alcohol - pelvic floor exercises - psychosexual therapy if performance anxiety contributes Tablets treat **symptoms** — addressing **underlying vascular health** improves long-term outcomes and may reduce need for ongoing medication. ## What if PDE5 inhibitors fail? GP or urology referral for: - vacuum erection device — NHS prescription possible - intracavernosal alprostadil injections - urethral alprostadil pellets - testosterone if hypogonadism confirmed - penile implants — last resort ED is common and treatable — sildenafil and tadalafil help most men safely when prescribed appropriately. ## ! Important safety information for sildenafil and tadalafil Book a GP appointment for persistent ED — assessment includes cardiovascular risk, diabetes screening, and medicine review. Seek emergency help for erection over 4 hours (priapism). Do not buy unregulated online medicines — use GPhC-registered pharmacies. Tell your GP all medicines including recreational drugs before starting PDE5 inhibitors. ## Common questions about sildenafil and tadalafil How much sildenafil should I take? Standard starting dose 50mg taken 30 to 60 minutes before sex — adjust to 25mg if side effects or 100mg if insufficient response. Maximum one dose per 24 hours. Generic sildenafil is identical to Viagra — same active ingredient, lower cost. Can I take tadalafil every day? Yes — tadalafil 2.5mg or 5mg daily provides continuous effect — useful if you prefer spontaneity without timing doses. On-demand dosing is 10 to 20mg at least 30 minutes before sex, max once daily. Daily dosing suits men who have sex frequently or also have benign prostate enlargement (licensed indication at 5mg daily). Why did Viagra not work for me? Common reasons — insufficient dose, taking with heavy meal (sildenafil), lack of arousal, severe vascular disease, uncontrolled diabetes, low testosterone, or predominantly psychogenic ED. Try alternate PDE5 inhibitor, ensure arousal, or see GP for second-line options — vacuum device, injections, or referral. Are Viagra and Cialis available over the counter? Sildenafil 50mg (Viagra Connect) and tadalafil (some brands) are available from UK pharmacies after pharmacist consultation — no GP appointment needed for eligible men. Pharmacist checks safety — heart medicines, blood pressure, symptoms needing GP. NHS prescription often cheaper for regular use. What are common side effects of Viagra? Headache, facial flushing, indigestion, nasal congestion, dizziness, temporary blue-tinted vision (rare). Usually mild and short-lived. Chest pain during sex — stop and seek urgent help — could be cardiac event. Priapism — erection over 4 hours — emergency. Can I take Viagra with blood pressure tablets? Often yes — PDE5 inhibitors mildly lower blood pressure. Caution with alpha-blockers like tamsulosin — separate timing. Never with nitrates. Stable heart disease may allow use after cardiologist assessment — usually wait 6 months after heart attack. Unstable angina — contraindicated. ## Sources - [NHS — Sildenafil (Viagra)](https://www.nhs.uk/medicines/sildenafil-viagra/) - [NHS — Tadalafil (Cialis)](https://www.nhs.uk/medicines/tadalafil/) - [NHS — Erectile dysfunction](https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/)