How Long Does Cialis Last? Half-Life, Timing and Side Effects

An as-needed dose of Cialis lasts up to 36 hours. The FDA label says tadalafil improved erectile function compared with placebo up to 36 hours after dosing. That is why tadalafil is often called the weekend pill.

"Lasts" means the window in which sexual stimulation can produce an erection more easily. It does not mean a constant erection, and Cialis does nothing without arousal. An erection that lasts more than 4 hours is a medical emergency.

• Cialis as needed (5 to 20 mg): effect up to 36 hours.
• Cialis once daily (2.5 to 5 mg): taken every day at about the same time, so there is no dosing window to plan around.
• Sildenafil (Viagra) and vardenafil (Levitra): short-acting, with half-lives of about 4 hours and 4 to 5 hours.

Which schedule fits you is covered in our daily vs as-needed tadalafil guide.

Tadalafil's mean terminal half-life is 17.5 hours in healthy men, according to the CIALIS label. Half-life is the time the body takes to clear half of a dose. A long half-life is what produces the long window, and it is what makes a low daily dose possible: blood levels build to a steady state rather than spiking and dropping.

The label also notes that exposure is higher in older men and in men with reduced kidney function, which is why those groups get lower maximum doses. For example, men with severe kidney impairment or on dialysis are limited to 5 mg as needed, no more than once every 72 hours.

Most of a single dose is cleared within about 3 to 4 days. That is a general pharmacology rule of thumb: a drug is largely eliminated after about five half-lives, and five times 17.5 hours is roughly 88 hours. The label does not give a single clearance time, and it varies with age, liver and kidney function and other drugs you take.

This matters for two reasons. Side effects like back pain can last into the next day. And interactions can happen long after you took the pill, which is why the label's nitrate rule uses a 48-hour wait.

Tadalafil reaches peak blood levels between 30 minutes and 6 hours after a dose, with a median of 2 hours, per the label. Food does not change how it is absorbed, so it can be taken with or without a meal. The label simply says to take as-needed Cialis before anticipated sexual activity, without a fixed lead time. Many men take it a few hours ahead, and because the window is so long, timing is less critical than with sildenafil.

For starting doses, strengths and the rules for older men and kidney or liver problems, see our tadalafil dosage guide.

The most common Cialis side effects are headache, upset stomach, back pain and muscle aches. In the label's placebo-controlled studies of as-needed use, the rates were:

• Headache: 11% at 10 mg, 15% at 20 mg (5% on placebo)
• Dyspepsia (indigestion): 8% at 10 mg, 10% at 20 mg (1% on placebo)
• Back pain: 5% at 10 mg, 6% at 20 mg (3% on placebo)
• Myalgia (muscle aches): 4% at 10 mg, 3% at 20 mg
• Nasal congestion: 3%
• Flushing: 3%
• Pain in a limb: 3%

Back pain and muscle aches are tadalafil's signature side effect. The label says they generally started 12 to 24 hours after dosing and typically resolved within 48 hours, felt as a diffuse ache in the lower back, buttocks or thighs. About 0.5% of men stopped as-needed Cialis because of them.

Get emergency care for an erection lasting more than 4 hours, sudden vision loss in one or both eyes, sudden hearing loss or ringing in the ears, chest pain, or fainting. If side effects persist, a clinician can lower the dose or switch to the daily low dose.

Not on your own. The CIALIS label says the safety and effectiveness of combining Cialis with other PDE5 inhibitors or ED treatments have not been studied, and it tells patients not to take Cialis with other PDE5 inhibitors. Viagra (sildenafil) is a PDE5 inhibitor, so the label's answer is no.

Stacking two drugs that both lower blood pressure raises the risk of dizziness, fainting and side effects, and because tadalafil lingers for days, a Viagra taken "the next day" can still overlap with it. If one drug is not working, the safer move is to ask a clinician about a dose change or a switch.

The label warns that substantial alcohol, 5 or more units, with Cialis can lower blood pressure and cause dizziness, a faster heart rate or headache. A drink or two is a different situation from heavy drinking, but alcohol also blunts erections on its own. Because tadalafil stays active for a day or more, the caution applies to the whole window, not only the hour after the pill.

Do not take Cialis if you use any nitrate or a guanylate cyclase stimulator such as riociguat. The combination can cause a dangerous drop in blood pressure. If you develop chest pain after Cialis and a nitrate is medically necessary, the label says at least 48 hours should pass after your last dose, and only with close monitoring.

• Alpha-blockers and blood pressure drugs: combining them can lower blood pressure. See ED meds and blood pressure.
• Strong CYP3A4 inhibitors such as ketoconazole or ritonavir: the label caps as-needed Cialis at 10 mg no more than once every 72 hours, and daily Cialis at 2.5 mg.
• Heart disease: the label lists recent heart attack, unstable angina, recent stroke and uncontrolled blood pressure among the groups not studied. Sex itself has to be safe for your heart.
• Adcirca: tadalafil is also sold for pulmonary arterial hypertension. Do not take Cialis if you already take Adcirca.

As-needed Cialis gives a window of up to 36 hours per dose. Daily Cialis at 2.5 or 5 mg keeps a steady level so you do not plan around a pill. Daily dosing also treats urinary symptoms of an enlarged prostate (BPH), which the label covers. The trade-off is cost and pill count: about 30 tablets a month. We cover the full decision in daily vs as-needed tadalafil, and price it out in how much generic Cialis costs.

• CIALIS (tadalafil) prescribing information, Eli Lilly: half-life, 36-hour efficacy, absorption, adverse reactions, back pain timing, alcohol, nitrates, CYP3A4 limits, combination warning: DailyMed, CIALIS label (read 2026-10-30)
• Sildenafil half-life: DailyMed, VIAGRA label
• Vardenafil half-life: DailyMed, vardenafil hydrochloride tablet
• Patient overview: MedlinePlus, Tadalafil
• HealthyMale tadalafil and Cialis listings: healthymale.com/erectile-dysfunction (checked 2026-10-30)