Sildenafil vs Tadalafil: Onset, Duration, Side Effects

Sildenafil (the drug in Viagra) and tadalafil (the drug in Cialis) are two of the most widely used tablets for erectile dysfunction. Both are FDA-approved for ED, both block the same enzyme (PDE5), and neither works without sexual stimulation. The differences that matter in daily life are timing, food, side-effect pattern and whether you want a daily option. This page compares them using the FDA prescribing information for each drug, the head-to-head trials, and current generic cash prices. For causes of ED and the non-drug options, start with our erectile dysfunction guide. If your concern is ejaculating too early rather than erections, see our premature ejaculation guide.

The molecule matters more than the brand name. Generic sildenafil and generic tadalafil contain the same active ingredient as the brands and are inexpensive (see the cost section below).

Sildenafil vs tadalafil at a glance

All figures below come from the two FDA labels on DailyMed: Viagra (sildenafil) — DailyMed Drug Label and Cialis (tadalafil) — DailyMed Drug Label.

	Sildenafil (Viagra)	Tadalafil (Cialis)
FDA-approved uses	Erectile dysfunction	Erectile dysfunction; benign prostatic hyperplasia (BPH); both together
When to take	About 1 hour before sex; anywhere from 30 minutes to 4 hours	As needed before sex, or once a day at about the same time
Peak blood level	30 to 120 minutes (median 60) on an empty stomach	30 minutes to 6 hours (median 2 hours)
How long it works	Effect seen up to 4 hours, weaker than at 2 hours	Better than placebo for up to 36 hours
Half-life	About 4 hours	17.5 hours (mean)
Food	A high-fat meal delays the peak by about 60 minutes	Not affected by food
As-needed doses	Start 50 mg; range 25 to 100 mg; at most once a day	Start 10 mg; range 5 to 20 mg; at most once a day
Daily option	None	2.5 mg, may increase to 5 mg (5 mg for BPH)

Which works faster: sildenafil or tadalafil?

On paper, they start at a similar time. The Viagra label says most men take sildenafil about an hour before sex, but it may be taken anywhere from 30 minutes to 4 hours beforehand. Peak blood levels arrive within 30 to 120 minutes, with a median of 60 minutes on an empty stomach (Viagra (sildenafil) — DailyMed Drug Label).

The Cialis patient information says sex may be possible from 30 minutes after a dose. Tadalafil's peak blood level comes later, between 30 minutes and 6 hours, with a median of 2 hours (Cialis (tadalafil) — DailyMed Drug Label). So if speed is the only goal, sildenafil on an empty stomach peaks sooner; tadalafil's advantage is its longer window, which the label tells prescribers to take into account when advising on timing.

Food and timing

Food is a real difference. A high-fat meal slows sildenafil: the label reports a mean delay of 60 minutes in reaching peak level and a 29% lower peak concentration, though it can still be taken with or without food (Viagra (sildenafil) — DailyMed Drug Label). Tadalafil's absorption is not influenced by food, so it can be taken with a meal without a delay (Cialis (tadalafil) — DailyMed Drug Label).

How long do they last? Duration and half-life

This is the headline difference. Sildenafil and its active breakdown product each have a half-life of about 4 hours. In the label's time-course study, sildenafil's effect lasted up to 4 hours, but the response at 4 hours was weaker than at 2 hours (Viagra (sildenafil) — DailyMed Drug Label).

Tadalafil's mean half-life is 17.5 hours. The Cialis label says an as-needed dose improved erectile function compared with placebo for up to 36 hours. In one of the label's trials, 61% of men on tadalafil 20 mg reported at least one successful intercourse about 24 hours after the dose (versus 37% on placebo), and 64% at about 36 hours (versus 37%) (Cialis (tadalafil) — DailyMed Drug Label).

A longer window does not mean a 36-hour erection. Both drugs only help an erection happen in response to sexual stimulation. An erection lasting more than 4 hours needs immediate medical help with either drug (Viagra (sildenafil) — DailyMed Drug Label; Cialis (tadalafil) — DailyMed Drug Label); see the safety box below.

Is one more effective? What head-to-head trials show

Direct head-to-head trials find them about equally effective; analyses that add indirect comparisons favour sildenafil.

• Direct comparisons. A meta-analysis of 16 trials that compared tadalafil with sildenafil directly found similar efficacy and similar overall side-effect rates. Tadalafil improved psychological outcomes such as sexual confidence more, and men and their partners preferred it PMID: 28741090.
• An older systematic review. In a systematic review funded by the US Agency for Healthcare Research and Quality, four head-to-head trials of sildenafil, vardenafil and tadalafil found no difference in ED improvement or side effects, though many of those trials were of low quality PMID: 19884626.
• Network meta-analyses. These mix direct and indirect comparisons, and they lean towards sildenafil on efficacy. One network meta-analysis of 82 trials found sildenafil 50 mg had the greatest efficacy of the starting doses but also the highest rate of side effects, while tadalafil 10 mg had intermediate efficacy and the lowest side-effect rate PMID: 25817916. A 2026 network meta-analysis of 83 placebo-controlled trials concluded that sildenafil showed significantly greater efficacy than the other PDE5 inhibitors, while tadalafil had the lowest odds of treatment-related side effects; two of its authors are Viatris employees, and Viatris markets Viagra PMID: 42296271.
• The overall picture. An overview of 23 systematic reviews concluded that the evidence directly comparing different PDE5 inhibitors is limited, that rankings favouring sildenafil came mainly from indirect comparisons, and that better head-to-head trials are needed PMID: 34557099.

In short, the head-to-head trials show no clear winner, and the rankings that favour sildenafil rest largely on indirect comparisons. Timing, side effects and cost are reasonable grounds for choosing, and a clinician can switch you if the first one does not suit.

Which do men prefer?

When men try both, more of them choose tadalafil.

• In a double-blind crossover trial of 219 men, each drug was taken with its own dosing instructions. After trying both, 73% of evaluable men chose tadalafil for the extension period PMID: 15041116.
• In a crossover trial of 215 men starting treatment, 66% preferred tadalafil 20 mg and 34% sildenafil 50 mg, with no significant difference in side effects PMID: 14693299.
• In an open-label crossover trial of 367 men new to these drugs, where doses could be adjusted, 71% chose tadalafil and 29% sildenafil. Erectile function scores were similar on both (P = 0.08), while the rate of successful intercourse was higher on tadalafil (77% vs 72% of attempts, P = 0.003) PMID: 16287454.

These trials are from 2003 to 2005, when tadalafil was new, and preference may partly reflect dosing routine. Between about a quarter and a third of men in them still chose sildenafil.

Sildenafil vs tadalafil side effects

The side effects are broadly similar because both drugs widen blood vessels, but the pattern differs. The labels warn that side-effect rates from different drugs' trials cannot be compared directly, so read the figures below as each drug against its own placebo.

Sildenafil (Viagra). In flexible-dose trials, the most common side effects were headache (16% vs 4% on placebo), flushing (10% vs 1%), indigestion (7% vs 2%), nasal congestion (4% vs 2%) and abnormal vision (3% vs 0%), described as mild and short-lived, mostly a colour tinge, light sensitivity or blurring (Viagra (sildenafil) — DailyMed Drug Label).

Tadalafil (Cialis), as needed. At 10 or 20 mg, the most common were headache (11% to 15% vs 5%), indigestion (8% to 10% vs 1%), back pain (5% to 6% vs 3%), muscle aches (3% to 4% vs 1%), nasal congestion and flushing (3% each vs 1%). Back pain and muscle aches generally began 12 to 24 hours after a dose and typically settled within 48 hours (Cialis (tadalafil) — DailyMed Drug Label).

The direct-comparison meta-analysis matches this pattern: flushing was less common with tadalafil, while back pain and muscle aches were more common PMID: 28741090. A 2026 retrospective analysis of a direct-to-consumer telehealth database (132,100 patients on sildenafil, tadalafil or vardenafil) found similar side-effect rates at medium and high doses for sildenafil (35.0% of 10,201) and tadalafil (33.9% of 6,564), with reflux more common on tadalafil and flushing more common on sildenafil. The same analysis reported larger gains in satisfaction scores with sildenafil 50 to 100 mg than with tadalafil 10 to 20 mg. The data are self-reported by relatively healthy users rather than from a trial PMID: 41261009.

Daily tadalafil vs as needed

Tadalafil is the only one of the two with a once-daily option. The Cialis label recommends starting daily use at 2.5 mg, taken at about the same time every day without regard to timing of sex, and increasing to 5 mg if needed. Steady blood levels are reached within 5 days of daily dosing. Daily tadalafil is not recommended for people with severe kidney impairment (creatinine clearance under 30 mL/min or on dialysis) (Cialis (tadalafil) — DailyMed Drug Label).

In the label's 12-week trials of the daily dose, each compared with its own placebo group, tadalafil 5 mg a day was linked to headache in 6% (versus 5% on placebo), indigestion in 5% (versus 2%), and back pain and flushing in 3% each (versus 1% each) (Cialis (tadalafil) — DailyMed Drug Label).

On effectiveness, a meta-analysis of six randomized trials (1,596 men) found that tadalafil 5 mg a day for at least 6 months improved erectile function scores more than placebo and was well tolerated PMID: 32676425. The overview of systematic reviews found low-dose daily tadalafil may be slightly more effective than high-dose as-needed tadalafil, though the difference was small and only just statistically significant PMID: 34557099.

Daily dosing may suit men who would rather not plan a dose around sex, and at 5 mg it is also the approved dose for urinary symptoms from BPH (below).

Sildenafil vs tadalafil for BPH

Tadalafil is FDA-approved for the urinary symptoms of BPH, and for men who have both BPH and ED, at 5 mg once a day. The label says tadalafil is not recommended together with alpha-blockers when the aim is to treat BPH (Cialis (tadalafil) — DailyMed Drug Label). The Viagra label lists erectile dysfunction as sildenafil's only indication (Viagra (sildenafil) — DailyMed Drug Label). If you have both ED and urinary symptoms, this is one of the clearest reasons to ask about tadalafil.

Sildenafil or tadalafil with alcohol

The two labels say different things about alcohol. In one Viagra study, sildenafil 50 mg given with alcohol at 0.5 g/kg (enough for a peak blood alcohol of about 0.08%) did not increase alcohol's blood-pressure-lowering effect in healthy volunteers (Viagra (sildenafil) — DailyMed Drug Label).

The Cialis label notes that alcohol and tadalafil both widen blood vessels. Heavy drinking (5 units or more) with tadalafil can increase the chance of dizziness, a faster heart rate, a drop in blood pressure on standing, and headache (Cialis (tadalafil) — DailyMed Drug Label). The Viagra result comes from a single dose of alcohol at that level in healthy volunteers, so it is not a reason to drink heavily with either drug.

Can sildenafil and tadalafil be taken together?

No. Both labels say that combining the drug with other PDE5 inhibitors or other ED treatments has not been studied. The Viagra label adds that such combinations may further lower blood pressure and are not recommended, and the Cialis label tells patients not to take tadalafil with other PDE5 inhibitors (Viagra (sildenafil) — DailyMed Drug Label; Cialis (tadalafil) — DailyMed Drug Label).

The same applies to any compounded product that combines PDE5 inhibitors; the labels do not support combining them. FDA states that compounded drugs are not FDA-approved, meaning it does not verify their safety, effectiveness or quality before they are sold (FDA: Compounding and the FDA, questions and answers). This site does not recommend them. The labels also warn against combining an ED dose with Revatio (sildenafil for pulmonary arterial hypertension) or Adcirca (tadalafil) (Viagra (sildenafil) — DailyMed Drug Label; Cialis (tadalafil) — DailyMed Drug Label).

Interactions that change the dose

Both drugs are broken down mainly by the liver enzyme CYP3A4, so some medicines raise their levels (Viagra (sildenafil) — DailyMed Drug Label; Cialis (tadalafil) — DailyMed Drug Label):

• Sildenafil. With ritonavir, the label sets the dose at 25 mg, no more than 25 mg in 48 hours. A 25 mg starting dose should be considered with strong CYP3A4 inhibitors such as ketoconazole or itraconazole, with erythromycin, in people over 65, and in people with liver impairment or severe kidney impairment (Viagra (sildenafil) — DailyMed Drug Label).
• Tadalafil. With potent CYP3A4 inhibitors such as ketoconazole or ritonavir, as-needed use is capped at 10 mg no more than once every 72 hours, and daily use at 2.5 mg (Cialis (tadalafil) — DailyMed Drug Label).
• Alpha-blockers. For either drug, the labels advise being stable on the alpha-blocker before starting, at the lowest dose (Viagra (sildenafil) — DailyMed Drug Label; Cialis (tadalafil) — DailyMed Drug Label).

Nitrates and riociguat must never be combined with either drug (Viagra (sildenafil) — DailyMed Drug Label; Cialis (tadalafil) — DailyMed Drug Label). The safety box below covers these and the other label warnings.

What about vardenafil and avanafil?

Two other PDE5 inhibitors, vardenafil (Levitra) and avanafil (Stendra), are also FDA-approved for ED PMID: 42296271. The two network meta-analyses do not rank them the same way. In the 82-trial analysis, vardenafil 10 mg and avanafil 100 mg had side-effect rates similar to sildenafil 50 mg but markedly lower overall efficacy at those starting doses PMID: 25817916. The 2026 dose-specific analysis, which measured the odds of reaching satisfactory erectile function compared with placebo, put vardenafil 10 mg (odds ratio 7.78) close to sildenafil 50 mg (7.90) and sildenafil 100 mg (9.06), and ahead of tadalafil 20 mg (7.13), tadalafil 10 mg (3.14) and avanafil 200 mg (3.42) and 100 mg (1.75). In that analysis, vardenafil had the highest odds of treatment-related side effects, and its authors note that wide confidence intervals make some of these estimates uncertain PMID: 42296271. Rankings like these do not settle the choice for an individual; the American Urological Association guideline recommends shared decision-making about every suitable treatment PMID: 29746858.

If you cannot or prefer not to take a PDE5 inhibitor, there are non-drug options, which are medical devices rather than drugs: the over-the-counter Eroxon gel, which FDA authorized through its De Novo pathway (FDA De Novo record DEN220078), and vacuum erection devices. The evidence for each is covered in the ED guide and in our reviews of Eroxon and the Encore Deluxe. For how Eroxon compares with Viagra, see our in-depth Eroxon review, and for vacuum devices, including their use alongside tadalafil after prostate surgery, our vacuum erection device guide.

Sildenafil vs tadalafil cost

Both drugs are available as inexpensive generics. The calculator below uses cash prices from Mark Cuban Cost Plus Drug Company's public pricing API, checked on October 2, 2026. Per-tablet prices were $0.045 for generic sildenafil 50 mg (product page), $0.062 for generic tadalafil 10 mg (product page) and $0.0325 for generic tadalafil 5 mg (product page), plus a $5 dispensing fee per order and any shipping charge. You still need a prescription.

The monthly quantities are examples, not a recommendation: 8 as-needed doses a month, or one tablet a day for daily tadalafil. Choose one option; the dispensing fee is always added.

At these prices, the dispensing fee and shipping cost more than the tablets themselves, so ordering several months at once may lower the cost per month. Prices at other pharmacies, with insurance, and through telehealth services vary, so it is worth comparing.

Getting a prescription online

Both drugs need a prescription, and both labels ask prescribers to consider heart health and other medicines before prescribing (Viagra (sildenafil) — DailyMed Drug Label; Cialis (tadalafil) — DailyMed Drug Label). An online service does this through a questionnaire or video visit, though questionnaire-only intake can miss other health problems PMID: 32535075. The table below covers Ro ❔LegitScript status not verified, Hims ❔LegitScript status not verified and Lemonaid Health ❔LegitScript status not verified. Ro's and Lemonaid's ED pages were checked for this article on October 2, 2026, and both list ED medicines; Ro's pricing page was checked on October 3, 2026. Hims's site blocked automated access, so this page states nothing about its service beyond its badge. The badges show the LegitScript status this site could confirm; they currently read "not verified" because LegitScript's directory could not be queried (what this means). Ro and Lemonaid publish prices before a consultation (Ro pricing; Lemonaid, erectile dysfunction); Hims's could not be checked, so its price cell is blank. Our comparison of Hims, Ro, Hone and Lemonaid for ED covers each service in more detail.

Whichever route you choose, ask for the generic molecule by name. The drug is the same; the brand and the platform mainly change the price. Our methodology explains how this site rates evidence and what it earns.