Short answer: all three are PDE5 inhibitors with broadly similar efficacy. Tadalafil lasts much longer, sildenafil is most food-sensitive, and vardenafil uniquely carries a QT-prolongation warning — none is objectively "best" for everyone.
Sildenafil and tadalafil get most of the attention, but vardenafil is the third member of the original PDE5 inhibitor class — approved within months of tadalafil and pharmacologically distinct in a few specific ways. Here's how all three actually compare.
Same Mechanism, Three Different Molecules
All three drugs are selective inhibitors of PDE5, the enzyme that breaks down cGMP in the smooth muscle of the corpus cavernosum. Blocking that breakdown preserves the signal that allows increased blood flow into the penis during sexual stimulation.[2] Sildenafil got there first, approved March 27, 1998, followed by vardenafil on August 19, 2003, and tadalafil shortly after, on November 21, 2003.[3]
At a Glance
| Drug | Onset | Half-life | Food effect | FDA approved |
|---|---|---|---|---|
| Sildenafil (Viagra) | ~30–60 min | ~4 hours | Delayed/reduced by high-fat meal | 1998 |
| Vardenafil (Levitra) | ~30 min–2 hrs (median 60 min) | ~4–5 hours | Some sensitivity to food | 2003 |
| Tadalafil (Cialis) | ~30 min–2 hrs | ~17.5 hours | None significant | 2003 |
Vardenafil's label puts peak concentration at 30 minutes to 2 hours after dosing (median around 60 minutes), with the standard dose taken roughly an hour before activity.[1]Sildenafil's onset runs similarly fast, though a high-fat meal delays and can reduce its peak level.[3]Tadalafil's onset is a bit slower and more variable, but unlike sildenafil, food doesn't meaningfully affect it.[4] On half-life, vardenafil and sildenafil are close cousins — roughly 4 to 5 hours each — while tadalafil stands well apart at approximately 17.5 hours, the basis for its up-to-36-hour labeled window compared to the few-hour window of the other two.[1]
Potency Isn't the Same as Effectiveness
In lab measurements of raw binding potency (IC50 — the concentration needed to inhibit 50% of PDE5 activity), vardenafil comes out most potent at roughly 0.091 nmol/L, followed by tadalafil at about 1.8 nmol/L, with sildenafil the least potent of the three at about 3.7 nmol/L.[2]That sounds like it should translate to real-world superiority for vardenafil — but a pharmacotherapy review notes there's no current evidence that this greater in vitro potency actually produces superior clinical results.[5]A 2025 systematic review found sildenafil produced effective erections in 77% to 84% of participants at standard doses, and separately highlighted tadalafil's "weekend pill" reputation as coming specifically from its long duration rather than any efficacy edge.[6]
Where the Side-Effect Profiles Diverge
All three drugs show some cross-reactivity with PDE6, an enzyme concentrated in retinal photoreceptors — sildenafil and vardenafil show "low activity" against it, while tadalafil shows "very low activity," reflecting greater selectivity for PDE5 over PDE6.[2] That selectivity difference is thought to explain why vardenafil and tadalafil are believed to produce fewer visual side effects than sildenafil.[5]
Vardenafil carries one FDA-labeled warning the other two don't have: a caution about QT interval prolongation. A clinical study in 59 healthy men found both a therapeutic (10 mg) and a supratherapeutic (80 mg) dose of vardenafil produced measurable increases in QTc interval — comparable to an active control drug — with an additional, additive effect when combined with another QT-prolonging medication.[7]Based on that, vardenafil's label specifically advises against use in patients with congenital QT prolongation syndrome or those taking Class IA or Class III antiarrhythmic medications — a contraindication that doesn't appear on the sildenafil or tadalafil labels.[7]
Shared across all three: priapism (a painful erection lasting more than four hours) is an uncommon but documented risk requiring urgent medical care, and all three are metabolized through the same liver enzyme pathway (CYP3A4) — which is why all three carry similar interaction warnings for strong CYP3A4 inhibitors like certain antifungal and HIV medications.[2]
The Bottom Line
The three drugs are more alike than different — same mechanism, broadly similar efficacy, similar core risks. Where they genuinely diverge is duration (tadalafil's the clear outlier), food sensitivity (sildenafil's the one to plan meals around), and one cardiac-specific warning unique to vardenafil. None of these differences make one objectively better; they just point toward different fits depending on your health history and how you want to plan around the medication.
Providers vary in which of the three they prescribe by default — compare options on RENVA's Men's Health / TRT hub if you have a preference or a health history that makes one option better suited to you.
Sources
- LEVITRA (vardenafil HCl) tablets — Full Prescribing Information — U.S. Food and Drug Administration accessdata.fda.gov
- PDE5 inhibitors – pharmacology and clinical applications 20 years after sildenafil discovery — PMC (National Institutes of Health) pmc.ncbi.nlm.nih.gov
- VIAGRA (sildenafil citrate) — Full Prescribing Information — U.S. Food and Drug Administration accessdata.fda.gov
- CIALIS (tadalafil) tablets, for oral use — Full Prescribing Information — U.S. Food and Drug Administration accessdata.fda.gov
- Pharmacotherapy Update: New Competition for Viagra — Cleveland Clinic Center for Continuing Education clevelandclinicmeded.com
- Comparative Efficacy and Safety of Sildenafil, Tadalafil, Vardenafil — PMC (National Institutes of Health) pmc.ncbi.nlm.nih.gov
- STAXYN (vardenafil) — Full Prescribing Information — U.S. Food and Drug Administration accessdata.fda.gov
Frequently Asked Questions
Is vardenafil stronger than sildenafil or tadalafil?
It has higher lab-measured potency, but there's no evidence this translates into better real-world results — clinical effectiveness across the three is broadly comparable.[5]
What's unique about vardenafil's safety profile?
It carries an FDA warning about QT interval prolongation not found on sildenafil or tadalafil labels, and is contraindicated in patients with congenital QT prolongation syndrome or on certain antiarrhythmic medications.[7]
Which of the three lasts the longest?
Tadalafil, by a wide margin — its half-life of about 17.5 hours supports effectiveness up to 36 hours, compared to a few hours for sildenafil and vardenafil.[1]
Does food affect all three the same way?
No. Sildenafil is the most food-sensitive — a high-fat meal delays and reduces its peak concentration. Vardenafil has some sensitivity, while tadalafil is not meaningfully affected by food.[3]