Viagra vs Cialis: which lasts longer and which suits you?

Medically reviewed by Muhammad A Jalil, Superintendent Pharmacist (GPhC Reg No: 2236161)

Published 2026-08-22 · Clinically reviewed 2026-08-22 · Updated 2026-08-23

Viagra (sildenafil) lasts around four to six hours; Cialis (tadalafil) up to 36. How the two compare on speed, food, side effects and daily use.

Viagra and Cialis — better known to prescribers as sildenafil and tadalafil — are the two most used erectile dysfunction tablets in the UK, and at licensed doses they are similarly effective. The real difference is time: sildenafil works for around four to six hours, while tadalafil lasts up to 36 and also comes as a low-strength daily tablet. Which suits you better comes down to how you live, not which is "stronger" — and it is a decision to make with a prescriber.

How do they work?

Both belong to the same family, the PDE5 inhibitors. During arousal, blood vessels in the penis release signals that relax muscle and let blood flow in; an enzyme called PDE5 switches those signals off. Blocking PDE5 keeps the signals working for longer, making an erection easier to get and keep. That mechanism explains a rule that applies to both tablets: without sexual stimulation, neither does anything at all.

How do they compare at a glance?

	Sildenafil (Viagra)	Tadalafil (Cialis)
Starts working	30–60 minutes	30 minutes–2 hours
Lasts	Around 4–6 hours	Up to 36 hours
Affected by food	Yes — fatty meals delay it	Minimal effect
Dosing	As needed: 25, 50 or 100 mg	As needed: 10 or 20 mg; or daily: 2.5 or 5 mg
Suits	Planned occasions	Spontaneity, frequent sex

Both are long off-patent, so the generic versions prescribed in the UK contain the same active ingredients as the original brands.

How long does each one last?

Sildenafil gives a window of roughly four to six hours — comfortably enough for an evening, gone by morning. Tadalafil stays active for up to 36 hours, which is why it earned the nickname "the weekend pill": a Friday-evening dose can still be working on Sunday morning. Lasting longer does not mean a 36-hour erection; it simply means that whenever arousal happens inside that window, the tablet is there to help.

How quickly do they work?

Sildenafil is usually effective from about half an hour, peaking around the hour mark. Tadalafil's onset is more variable — some men respond within 30 minutes, others need closer to two hours — but because it lasts so long, precise timing matters far less. The daily 2.5 mg or 5 mg tadalafil option removes timing from the equation entirely: after a few days of steady dosing there is a continuous background effect, with no tablet to remember in the moment.

What about food and alcohol?

This is a genuinely practical difference. A heavy or fatty meal can delay sildenafil by an hour or more and weaken its peak, so it performs best on an empty or lightly filled stomach. Tadalafil is largely unaffected by food. Alcohol undermines erections with either tablet — a drink or two is fine, but heavy drinking works directly against the medicine.

Do the side effects differ?

The shared side effects are those of widened blood vessels: headache, facial flushing, blocked nose and indigestion, usually mild and short-lived. Sildenafil occasionally causes a temporary blue-green tinge to vision; tadalafil is slightly more associated with back pain and muscle aches, likely because it lingers longer. Neither may ever be combined with nitrate heart medicines or with poppers (amyl nitrite) — the combination can drop blood pressure dangerously — and men taking alpha-blockers for prostate or blood pressure problems need doses timed carefully. Seek urgent help for sudden vision or hearing loss, or an erection lasting over four hours.

Which one suits you?

Think about pattern rather than power. If sex tends to be planned and occasional, sildenafil's shorter window is easy to work with. If you value spontaneity, find timing pressure stressful, or are sexually active twice a week or more, tadalafil — particularly the daily dose — often fits better. Cost differences between generics are modest either way. A prescriber will also weigh your heart health, other medicines and any previous experience with either tablet before recommending one; some men simply respond better to one than the other, and switching is straightforward with guidance.

Frequently asked questions

Is one stronger than the other?

No. At licensed doses their success rates in trials are similar. "Stronger" usually turns out to mean "suited my circumstances better" — duration, food sensitivity and timing differ far more than effectiveness.

Can I take them together, or on the same day?

Never. Combining two PDE5 inhibitors stacks their blood-pressure effects without improving results. Leave a clear gap, as advised by your prescriber, when switching from one to the other.

Can I switch if the first one disappoints?

Yes — non-response to one tablet does not predict failure with the other, and switching is a standard next step after a fair trial of six to eight attempts. Our guide on what to do when sildenafil doesn't work covers the groundwork worth checking first.

Do either of them increase sex drive?

No. Both act on blood flow, not desire. If low libido is the main issue, that points to different causes — hormones, mood, medicines or relationship factors — and is worth raising in a consultation.

The safest route to either medicine is a proper medical assessment rather than guesswork. You can check your eligibility for erectile dysfunction treatment online in a few minutes — a UK prescriber reviews every consultation and helps you choose the option that fits your health and your life.