Tadalafil: What It Is, How Cialis Works and What It Is Used For

This page covers what tadalafil is, what it is used for, how it works, how long it lasts, food and alcohol, side effects from its label, and who sells it. Generic tadalafil tablets carry the same FDA labeling as the brand. We do not give doses; the prescriber sets the strength.

What is Cialis?

Cialis is the brand name for tadalafil tablets, made by Eli Lilly. The label's first page reads "Initial U.S. Approval: 2003". Generic tadalafil is approved by the FDA as the same active drug, and it is what most online programs sell.

Gummies, chews and sublingual tablets that contain tadalafil are different. A pharmacy mixes them, and they are not FDA-approved products. Every plan in our price tables says which kind it is.

Tadalafil uses: what is tadalafil used for?

The Cialis label lists three uses (DailyMed: Cialis label):

• Erectile dysfunction (ED). "CIALIS ® is indicated for the treatment of erectile dysfunction (ED)."
• Enlarged prostate. "CIALIS is indicated for the treatment of the signs and symptoms of benign prostatic hyperplasia (BPH)." BPH is a non-cancer growth of the prostate that makes peeing harder.
• Both together. "CIALIS is indicated for the treatment of ED and the signs and symptoms of BPH (ED/BPH)."

MedlinePlus, the US National Library of Medicine's drug guide, adds the fourth use. "Tadalafil (Adcirca) is used to improve the ability to exercise in people with pulmonary arterial hypertension", which is high blood pressure in the lung arteries (MedlinePlus: tadalafil, read 14 November 2026). Adcirca and Cialis are the same drug sold under different names for different conditions.

For the prostate, MedlinePlus lists the symptoms it helps: "difficulty urinating (hesitation, dribbling, weak stream, and incomplete bladder emptying), painful urination, and urinary frequency and urgency". The prostate use relies on the daily form of the pill.

How does Cialis work?

An erection needs blood to flow into the penis. During arousal, nerves release nitric oxide, which raises a messenger called cGMP. cGMP relaxes the muscle in the penis so blood can flow in. An enzyme called PDE5 breaks cGMP down.

Tadalafil blocks PDE5. The label says "The inhibition of phosphodiesterase type 5 (PDE5) enhances erectile function by increasing the amount of cGMP. Tadalafil inhibits PDE5." It adds that "the inhibition of PDE5 by tadalafil has no effect in the absence of sexual stimulation". So it does not cause an erection by itself, and it does not raise desire.

The same effect on cGMP happens in the muscle of the prostate and bladder. The label says "The mechanism for reducing BPH symptoms has not been established", so nobody knows exactly why it helps the prostate.

How long tadalafil lasts

Tadalafil is the long-acting ED pill. The label says it improved erections compared with a dummy pill "up to 36 hours following dosing", and its half-life is 17.5 hours. Half-life is the time it takes for half of the drug to leave the blood. Sildenafil (Viagra) lasts a few hours.

A trial found "59.2% of intercourse attempts were successful" 36 hours after a dose, against 28.3% on placebo, which means a dummy pill (Porst et al., Urology 2003, PubMed). Our guide to how long Cialis lasts has the full timing.

Daily vs as-needed tadalafil

Tadalafil is sold two ways. As needed, a higher strength is taken before sex. Daily, a lower strength is taken every day, so timing stops mattering. The label says the daily form "provides continuous plasma tadalafil levels". Our daily tadalafil cost guide compares what each costs per month.

Tadalafil, food and alcohol

Food does not matter. The label says absorption is "not influenced by food; thus CIALIS may be taken with or without food".

Alcohol needs more care than with sildenafil. The label says "both alcohol and CIALIS, a PDE5 inhibitor, act as mild vasodilators", which means both widen blood vessels. Heavy drinking with it can cause dizziness, a fast heartbeat and a drop in blood pressure on standing. Tell the prescriber how much you drink.

Medicines that do not mix with tadalafil

Nitrates, the chest-pain drugs, are the firm rule. The label says "Administration of CIALIS to patients using any form of organic nitrate is contraindicated", which means you must not take them together. In an emergency, it says at least 48 hours should pass after the last dose before a nitrate is given. Riociguat, a lung blood pressure drug, is also off limits.

Alpha-blockers, other blood pressure drugs, and some antibiotics, antifungals and HIV drugs need care. Our ED pill side effects guide covers each group.

Tadalafil side effects

These are from Table 1 of the Cialis label: eight trials of as-needed use, highest strength tested, against a dummy pill (placebo).

Back pain is the tadalafil side effect. The label says it "generally occurred 12 to 24 hours after dosing and typically resolved within 48 hours" (Cialis label). A pooled study of many ED trials found tadalafil "had the lowest overall rate of all adverse events" of the pills compared, at usual starting strengths (Chen et al., Eur Urol 2015, PubMed). Adverse events means side effects.

When to get help

The label tells patients with "an erection lasting greater than 4 hours, whether painful or not" to "seek emergency medical attention". Sudden loss of vision or hearing also needs urgent care.

Who sells generic tadalafil, and what it costs

These programs publish a price that includes the visit. The table is ranked on our score. Prices come from each seller's own page, as checked November 14, 2026.

Every plan, strength and read date is on our tadalafil price page. The per-pill cost guide adds the cash price with your own prescription, and Best online ED programs ranks every program.