In short
- Viagra (sildenafil) is taken 30 minutes to 4 hours before sex; Cialis (tadalafil) improved erections for up to 36 hours after one dose in trials.
- Only Cialis is approved for daily use (2.5 mg or 5 mg) and for symptoms of an enlarged prostate (BPH).
- In Viagra’s trials, 63% to 82% of men reported improved erections depending on dose, against 24% on placebo.
- In a Cialis trial, 64% of men on 20 mg had successful sex 33 to 39 hours after a dose, against 37% on placebo.
- Brand-name Viagra cost $96 to $139 a dose online on October 18, 2026, and brand-name Cialis from $29; their generics cost $1.60 to $7.25 a dose.
Viagra and Cialis both treat erectile dysfunction by blocking an enzyme called PDE5, which lets more blood flow into the penis when you are aroused. Neither causes an erection on its own. The main difference is timing. Viagra (sildenafil) is taken 30 minutes to 4 hours before sex and covers one occasion. Cialis (tadalafil) improved erections for up to 36 hours after one dose in trials, and it is the only ED pill approved as a low daily dose.
Two other pills are approved for ED: vardenafil, once sold as Levitra, and avanafil, sold as Stendra. Below is how all four compare on timing, results, side effects and price, and which tends to suit whom.
The four approved ED pills
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| Viagra (sildenafil) | Cialis (tadalafil) | Vardenafil (Levitra) | Stendra (avanafil) | |
|---|---|---|---|---|
| When to take it | 30 min to 4 h before sex, about 1 h for most | Before sex, or once daily | About 60 min before sex | As early as about 15 min before sex |
| Peak level in the blood | Median 60 min | Median 2 h | 30 min to 2 h | Median 30 to 45 min |
| Half-life | About 4 h | 17.5 h | About 4 to 5 h | About 5 h |
| Food | High-fat meal delays it about 1 h | No effect | With or without food | High-fat meal delays it about 1 h |
| Daily dosing approved | No | Yes, 2.5 or 5 mg | No | No |
| Other approved uses | Pulmonary hypertension (as Revatio) | BPH; pulmonary hypertension (as Adcirca) | None | None |
| First approved | Mar 27, 1998 | Nov 21, 2003 | Aug 19, 2003 | Apr 27, 2012 |
Figures are from each drug’s FDA label on DailyMed and its Drugs@FDA record. Drugs@FDA lists the Levitra brand and its dissolving version, Staxyn, as discontinued; generic vardenafil tablets are still made. All four are prescription-only.
How long each one lasts
“Half-life” is the time it takes for half of a dose to leave the body. Sildenafil’s is about 4 hours and tadalafil’s 17.5 hours, which is why tadalafil’s window is so much longer.
The Cialis label reports a trial built around that window. Men took 20 mg and then tried to have sex a day or a day and a half later. At 22 to 26 hours, 61% had at least one successful attempt, against 37% on placebo. At 33 to 39 hours, 64% did, against 37%.
The Viagra label allows it to be taken anywhere from 30 minutes to 4 hours before sex. In practice, sildenafil suits a planned evening and tadalafil a weekend, or any time if you take it daily.
How well they work
The labels report results in different ways, so the numbers aren’t directly comparable, but both drugs worked for most men in their trials:
- Viagra: in four 12- to 24-week trials of 1,797 men, 63% on 25 mg, 74% on 50 mg and 82% on 100 mg reported improved erections, against 24% on placebo. The men’s ED had a range of causes, including diabetes.
- Cialis: tested in 22 trials of up to 24 weeks with more than 4,000 men for as-needed use, and in three trials with 853 men for daily use, it improved erectile function over placebo, including in studies of men with diabetes and, for as-needed use, men after prostate surgery.
- Vardenafil: in four 3-month trials of 2,431 men, each dose (5, 10 and 20 mg) improved erectile function scores over placebo.
- Stendra: in four 2- to 3-month trials, avanafil improved erectile function over placebo; one trial measured success starting about 15 minutes after a dose.
No head-to-head trial is reported on these labels. If one drug doesn’t work for you at the full dose, a clinician may suggest trying another.
Side effects
Side effects are similar across the class: headache, flushing, indigestion and a stuffy nose. These rates are from each label’s table of men taking the drug as recommended, against placebo:
Scroll sideways to see the full table
| Side effect | Viagra (flexible dose) | Its placebo | Cialis 10 mg / 20 mg as needed | Its placebo |
|---|---|---|---|---|
| Headache | 16% | 4% | 11% / 15% | 5% |
| Flushing | 10% | 1% | 3% / 3% | 1% |
| Indigestion | 7% | 2% | 8% / 10% | 1% |
| Stuffy nose | 4% | 2% | 3% / 3% | 1% |
| Back pain | 2% | 2% | 5% / 6% | 3% |
| Vision changes | 3% | 0% | not listed |
Viagra’s vision changes were mild and brief, mostly a color tinge to vision, sensitivity to light or blurring. Cialis is more often linked with back and muscle pain. On daily Cialis at 2.5 mg and 5 mg, side effects were less common, for example headache in 3% and 6% of men against 5% on placebo.
Who should avoid them
The same warnings apply to all four. Never take them with nitrates (such as nitroglycerin or “poppers”) or riociguat, because blood pressure can drop dangerously. Don’t combine them with each other: both labels say combinations haven’t been studied and may lower blood pressure further. The Viagra label adds that there are no controlled data in men who had a heart attack, stroke or life-threatening arrhythmia in the last 6 months, or who have very low or very high blood pressure, so a clinician must weigh those cases carefully. Vardenafil can also prolong the QT interval of the heart rhythm. Get emergency care for an erection lasting more than 4 hours.
What they cost in October 2026
| Medication | Brand-name price | Generic price |
|---|---|---|
| Viagra / sildenafil | $96 a dose (Rex MD), $139 (Hims) | $1.60 to $6.25 a dose |
| Cialis / tadalafil, as needed | From $29 a dose (Rex MD) | $3 to $7.25 a tablet |
| Cialis / tadalafil, daily | $958 a month (Hims) | From $40 a month |
| Vardenafil | Brand discontinued | Not priced by the providers we track |
| Stendra / avanafil | Not priced by the providers we track | Not priced by the providers we track |
Prices are from each provider’s own site, read October 18, 2026. Generic sildenafil and tadalafil are FDA-approved and contain the same active ingredients at the same strengths as the brands. Compounded chewables are not: they are not Viagra or Cialis, not generics of them, and not FDA-approved. Our guides to Viagra’s cost and Cialis’s cost list every price.
Which fits you
- For a planned evening, sildenafil is cheap, well studied and has the shorter half-life.
- For a weekend, or more spontaneity, a single dose of tadalafil can last up to 36 hours.
- To stop planning altogether, daily tadalafil at 2.5 or 5 mg keeps you ready at any time.
- With an enlarged prostate, daily tadalafil 5 mg is approved for both ED and BPH symptoms.
- If you want the fastest start, avanafil is labeled for use as early as about 15 minutes before sex, though few online providers offer it.
A licensed clinician will weigh these against your heart health, other medicines and how often you have sex. Our sildenafil vs tadalafil guide goes deeper on the two generics, and the ED rankings compare where to get them. See also Viagra and Cialis.
The bottom line
Viagra and Cialis both worked for most men in their trials. Viagra covers one occasion, taken 30 minutes to 4 hours ahead; Cialis lasts up to 36 hours, comes as a daily dose and also treats BPH. As generics, both cost a few dollars a dose as of October 2026, while the brands cost many times more. Pick by timing and health first, then by price.
Questions, answered
Is Cialis better than Viagra?
Can I take Viagra and Cialis together?
Which works faster, Viagra or Cialis?
Which is cheaper, Viagra or Cialis?
Sources
- Viagra prescribing information (Viatris, DailyMed, rev. 11/2023)
- Cialis prescribing information (Eli Lilly, DailyMed, rev. 06/2026)
- Vardenafil hydrochloride tablets prescribing information (DailyMed, rev. 08/2026)
- Avanafil tablets prescribing information (Camber, DailyMed, rev. 12/2025)
- Drugs@FDA: Viagra, NDA 020895
- Drugs@FDA: Cialis, NDA 021368
- Drugs@FDA: Levitra, NDA 021400 (discontinued)
- Drugs@FDA: Stendra, NDA 202276
- Rex MD: branded Viagra and Cialis (read Oct 18, 2026)
- Hims: Viagra (read Oct 18, 2026)