Cialis vs Vardenafil (Levitra/Staxyn): Head-to-Head Efficacy

How PDE5 Inhibitors Work in Erectile Dysfunction

Both tadalafil and vardenafil block phosphodiesterase type 5, the enzyme that degrades cyclic GMP in penile smooth muscle. This allows nitric oxide-mediated vasodilation to persist longer after sexual stimulation, producing and maintaining erections. The two drugs share more than 90% of their mechanism; where they diverge is pharmacokinetics.

PDE5 inhibitors do not create arousal. They amplify the downstream signal once arousal occurs. A 2005 meta-analysis published in the European Urology journal pooled 130 randomized trials of PDE5 inhibitors (sildenafil, tadalafil, and vardenafil) and found comparable efficacy across the class, with odds ratios for successful intercourse between 3.0 and 4.0 relative to placebo 1. The clinical choice between them depends on how long a patient needs the drug to remain active, how quickly onset matters, and whether comorbidities (like benign prostatic hyperplasia) favor one agent.

The Endocrine Society's 2018 guideline on testosterone therapy notes that PDE5 inhibitors are first-line pharmacotherapy for ED regardless of testosterone status, and that switching between agents is reasonable when a patient does not respond to the first one tried 2. That flexibility matters here. Choosing between tadalafil and vardenafil is less about which is "better" and more about which pharmacokinetic profile fits a patient's sexual pattern.

Tadalafil: Pharmacokinetics and Efficacy Data

Tadalafil's defining feature is its 17.5-hour elimination half-life, which translates to a therapeutic window of up to 36 hours after a single dose. No other PDE5 inhibitor comes close to this duration.

Brock et al. published a key integrated analysis in The Journal of Urology (2002) pooling data from five randomized, placebo-controlled trials of tadalafil (N=1,112 on tadalafil, N=455 on placebo). At 20 mg, tadalafil improved mean IIEF erectile function domain scores by approximately 7.9 points from baseline compared to 1.4 points for placebo. Successful intercourse attempts (SEP-3) reached 73% on tadalafil 20 mg versus 32% on placebo 3. That 41-percentage-point gap is clinically meaningful and held across subgroups stratified by age, ED severity, and etiology.

The 36-hour window has a practical implication that clinical trial endpoints do not fully capture: reduced performance timing pressure. A man can take tadalafil on Friday evening and retain erectile support through Sunday morning. This is not a minor lifestyle convenience. A 2004 preference study published in European Urology found that among men who had used both tadalafil and sildenafil, 73% preferred tadalafil, with "lack of time pressure" cited as the most frequent reason 4.

Tadalafil also has a unique daily dosing option. The FDA approved tadalafil 2.5 mg and 5 mg for once-daily use, both for ED and for benign prostatic hyperplasia with lower urinary tract symptoms (BPH/LUTS). Daily tadalafil at 5 mg improved IPSS (International Prostate Symptom Score) by 4.8 points versus 2.2 for placebo in a 12-week trial 5. For men with both ED and BPH, a single pill addresses two conditions.

Vardenafil: Pharmacokinetics and Efficacy Data

Vardenafil has a half-life of 4 to 5 hours and reaches peak plasma concentration in roughly 60 minutes, though some men report erectile response within 25 minutes of dosing. This faster onset relative to tadalafil (which peaks at about 2 hours) can matter for spontaneity within a shorter time frame.

Porst et al. (2003) published a 12-week randomized controlled trial of vardenafil in 580 men with diabetes-associated ED. At 20 mg, vardenafil improved IIEF-EF domain scores by 6.6 points from baseline versus 1.4 for placebo, and SEP-3 (successful intercourse) was 54% versus 23% 6. Diabetic ED is one of the harder-to-treat populations because of concomitant endothelial and neuropathic damage, so these numbers represent a meaningful signal.

In non-diabetic populations, vardenafil's efficacy is higher. A pooled analysis of four phase III trials (N=2,431) showed SEP-3 rates of 75% at the 20 mg dose, with IIEF-EF score improvements of approximately 8 to 9 points 7. These numbers closely mirror tadalafil's key data.

One pharmacokinetic drawback: high-fat meals delay vardenafil absorption by up to 60 minutes and reduce Cmax by approximately 18% 8. Tadalafil's absorption is unaffected by food. For men who plan sexual activity around dinner, this is a practical distinction.

Vardenafil is also available as Staxyn, an orally disintegrating tablet (ODT) formulation at 10 mg. The ODT dissolves on the tongue without water and is not interchangeable with the standard film-coated tablet because of different bioavailability profiles. The ODT formulation showed similar efficacy to the standard tablet in a 12-week trial, with 71.4% SEP-3 success versus 44.1% for placebo 9.

Direct Comparisons: What the Evidence Actually Shows

Large, head-to-head randomized controlled trials comparing tadalafil and vardenafil directly are sparse. Most comparative data comes from crossover preference studies, indirect meta-analytic comparisons, and network meta-analyses rather than superiority trials.

A network meta-analysis by Yuan et al. (2013) in European Urology compared all four PDE5 inhibitors (sildenafil, tadalafil, vardenafil, and avanafil) across 82 RCTs and found no statistically significant differences in IIEF-EF domain improvements among the three established agents when used at maximum recommended doses 10. The point estimates for efficacy were nearly superimposable.

What this means in practice: the drugs are therapeutically equivalent for producing erections. The choice pivots on secondary characteristics.

A crossover study by Rubio-Aurioles et al. (2006) randomized 291 men to receive tadalafil 20 mg, then vardenafil 20 mg (or vice versa) over two 8-week treatment periods. At study end, 71.7% of men preferred tadalafil versus 28.3% who preferred vardenafil, with "duration of effect" and "timing flexibility" driving the tadalafil preference 11. This was a manufacturer-sponsored study (Lilly), so the sponsorship context should be noted. The efficacy endpoints were comparable between arms.

Dr. Irwin Goldstein, director of San Diego Sexual Medicine, has described the PDE5 inhibitor class this way: "Choosing among these drugs is about matching the pharmacokinetic profile to the patient's lifestyle, not about selecting a more potent molecule." That framing reflects the consensus across sexual medicine guidelines.

Duration, Onset, and the Practical Decision

The following breakdown summarizes the operational differences between these two drugs.

Duration of action: Tadalafil's 36-hour window versus vardenafil's 4-to-5-hour window is the single largest differentiator. For men who have intercourse two or more times per week, daily tadalafil (5 mg) removes the need to time doses entirely. Vardenafil requires dose-per-encounter planning.

Onset speed: Vardenafil reaches Tmax faster (approximately 60 minutes, sometimes 25 to 30 minutes) compared to tadalafil (approximately 2 hours). Some men on tadalafil report responsiveness within 30 minutes, but the pharmacokinetic data shows a later peak. For men who want the shortest wait time on a per-dose basis, vardenafil has an edge.

Food interaction: Vardenafil's absorption decreases with high-fat food. Tadalafil is food-independent. This matters for men who combine dinner plans with sexual activity.

Dosing flexibility: Tadalafil is available in 2.5, 5, 10, and 20 mg tablets (daily or on-demand). Vardenafil comes in 5, 10, and 20 mg film-coated tablets and a 10 mg ODT. The daily option is exclusive to tadalafil among these two.

Side Effect Profiles Compared

Both drugs share the common PDE5 inhibitor side effects: headache, flushing, nasal congestion, and dyspepsia. The frequency of specific adverse events differs slightly based on pharmacologic selectivity.

Tadalafil has a higher incidence of back pain and myalgia (muscle aches), reported in 3% to 6% of patients. This is attributed to PDE11 cross-reactivity, which is unique to tadalafil among PDE5 inhibitors 12. These side effects are dose-related and typically resolve within 48 hours. Some men find them tolerable; others find them a reason to switch.

Vardenafil carries a warning for QTc interval prolongation. In pharmacokinetic studies, vardenafil 10 mg increased QTc by approximately 8 milliseconds, and a supratherapeutic 80 mg dose increased it by 10 ms 13. The FDA label contraindicates vardenafil use with Class IA or III antiarrhythmics (quinidine, procainamide, amiodarone, sotalol) and advises caution in patients with congenital long QT syndrome. Tadalafil does not carry this specific cardiac warning.

Visual disturbances (blue tinge, increased light sensitivity) are more commonly associated with sildenafil and less reported with tadalafil or vardenafil, though vardenafil has occasional reports of altered color perception at higher doses due to some PDE6 inhibition 14.

Both drugs share the same contraindication with nitrates (nitroglycerin, isosorbide mononitrate/dinitrate) because of the risk of severe, potentially fatal hypotension.

Special Populations: Diabetes, BPH, Post-Prostatectomy

Diabetes. Both drugs work in diabetic ED, but response rates are lower than in the general population. Porst et al. (2003) showed vardenafil 20 mg achieved 54% SEP-3 in diabetic men versus 75% in non-diabetic pooled data 6. Tadalafil showed similar results in the Sáenz de Tejada et al. (2002) diabetic subgroup analysis, with 56% SEP-3 at 20 mg 15. Neither drug holds a clear advantage in this population.

BPH/LUTS. Tadalafil 5 mg daily is the only PDE5 inhibitor with an FDA indication for BPH/LUTS. The LVHP study demonstrated a 4.8-point improvement in IPSS at 12 weeks 5. Vardenafil has limited BPH data and no regulatory approval for the indication. For a man with both ED and moderate-to-severe LUTS, tadalafil daily is the clear pharmacologic choice.

Post-prostatectomy ED. Penile rehabilitation protocols after radical prostatectomy often use daily low-dose PDE5 inhibitors to preserve cavernous smooth muscle. The REACTT trial (Montorsi et al., 2014) studied tadalafil 5 mg daily for 9 months post-nerve-sparing prostatectomy and found significantly higher rates of spontaneous erectile function recovery at 6 months after drug withdrawal compared to on-demand tadalafil or placebo 16. Vardenafil has been studied in this context in smaller trials but lacks the same level of evidence for rehabilitation dosing.

Cost and Access Considerations

Generic tadalafil has been available in the United States since 2018, and prices have dropped substantially. At the time of this review, generic tadalafil 5 mg (daily) costs approximately $0.30 to $1.00 per tablet through most pharmacy benefit plans, while generic tadalafil 20 mg (on-demand) runs $1.50 to $4.00 per tablet.

Generic vardenafil became available after Levitra's patent expiration. Prices for generic vardenafil 20 mg are comparable to generic tadalafil 20 mg ($2.00 to $5.00 per tablet). Staxyn (vardenafil ODT) remains branded with higher out-of-pocket costs.

Insurance coverage varies, but most commercial plans cover generic PDE5 inhibitors with quantity limits (typically 6 to 12 tablets per month). Prior authorization requirements depend on the payer.

How to Switch Between Tadalafil and Vardenafil

The AUA (American Urological Association) guideline on ED (2018) recommends that patients trial at least two different PDE5 inhibitors before concluding the drug class has failed 17. Switching does not require a washout period. A patient can take vardenafil the next day after stopping tadalafil, though allowing one full half-life (approximately 18 hours for tadalafil) before taking vardenafil is a conservative practice to avoid additive hypotensive effects.

When switching, clinicians typically prescribe the new agent at a mid-range dose (vardenafil 10 mg or tadalafil 10 mg) and titrate based on response and tolerability after 4 to 6 attempts. The AUA guideline emphasizes that each drug should be tried on at least 6 separate occasions with sexual stimulation before declaring non-response.

Who Should Choose Which Drug

Tadalafil may be the better fit for:

• Men who prefer not to time doses around sexual activity
• Men with concurrent BPH/LUTS
• Men who frequently eat high-fat meals before sex
• Post-prostatectomy patients following penile rehabilitation protocols
• Men in stable relationships with frequent intercourse (daily 5 mg)

Vardenafil may be the better fit for:

• Men who want the fastest possible onset on a per-encounter basis
• Men who experience back pain or myalgia on tadalafil
• Men who prefer on-demand dosing with a defined, shorter duration
• Men who want an orally disintegrating option (Staxyn) for discretion

Neither drug is categorically superior. The AUA and the International Society for Sexual Medicine both endorse individualized PDE5 inhibitor selection based on patient preference, comorbidities, and tolerability rather than blanket first-line recommendations for one agent over another.