Side-by-side table
| SildenafilViagra | TadalafilCialis | VardenafilLevitra, Staxyn | AvanafilStendra | |
|---|---|---|---|---|
| Usual start dose | 50 mg | 10 mg as needed, or 2.5–5 mg daily | 10 mg | 100 mg |
| Labeled range | 25–100 mg | 5–20 mg as needed | 5–20 mg | 50–200 mg |
| Take before sex | About 1 hour (30 min to 4 hours) | At least 30 minutes to 2 hours | About 1 hour | About 15–30 minutes |
| Window | About 4 hours | Up to 36 hours | About 4–5 hours | Several hours |
| High-fat meal | Delays onset | No real effect | Can delay tablets | Can delay onset slightly |
| Daily option | No | Yes | No | No |
| Generic in U.S. | Yes, since 2017 | Yes, since 2018 | Yes | Limited |
| Notable side effect | Blue-tinted or blurry vision | Back and muscle aches | Vision changes | Generally similar |
Doses above are the labeled starting points for healthy adults. Prescribers often start lower for men over 65, men with liver or kidney problems, and men taking interacting medications. Interactions →
Sildenafil (Viagra)
The original, approved in 1998, and still the most familiar. It's taken as needed, about an hour before sex, and works for roughly four hours.
- Food matters. A heavy, high-fat meal can delay it by about an hour and blunt the peak. Many men take it on an emptier stomach.
- Vision side effects. Because it also mildly affects an enzyme in the eye, some men notice a blue tint, blurriness, or light sensitivity. It's temporary.
- Cheap as a generic. Generic sildenafil arrived in late 2017. The same drug is also sold in 20 mg tablets (brand name Revatio, for a lung condition), which some prescribers use for flexible dosing.
Tadalafil (Cialis)
The long-acting option. Its effect lasts up to 36 hours, which is why it earned the nickname "the weekend pill."
- Less planning. The long window means sex doesn't have to be timed to a pill.
- Food doesn't matter. Absorption isn't meaningfully affected by meals.
- Daily dosing. It's the only one approved as a low daily dose (2.5 or 5 mg) for ED. The 5 mg daily dose is also approved for urinary symptoms from an enlarged prostate (BPH), which helps men who have both.
- Back and muscle aches are more common with tadalafil than the others, usually 12–24 hours after a dose.
- Lingers longer. The long duration also means a longer wait before nitrates could safely be given in an emergency (48 hours).
Vardenafil (Levitra, Staxyn)
Similar in timing to sildenafil: taken about an hour before sex, with a window of around four to five hours.
- Two forms. A standard tablet and a 10 mg tablet that dissolves on the tongue (originally sold as Staxyn). They're not interchangeable mg-for-mg, so don't swap one for the other without your prescriber.
- Heart rhythm caution. Its label warns about a small effect on the heart's QT interval, which matters for men with certain rhythm conditions or on related medications.
Avanafil (Stendra)
The newest of the four, approved in 2012, and the fastest to start: the 100 and 200 mg doses can work in about 15 minutes, and the 50 mg dose in about 30.
- More selective. It acts less on the related enzymes behind vision changes and muscle aches, though real-world side effect differences are modest.
- Usually costs more. Generic versions have been far less available than for sildenafil and tadalafil, so check the price before choosing it.
As-needed vs. daily
Most men take a PDE5 inhibitor only when they plan to have sex. Daily low-dose tadalafil is the alternative.
| As needed | Daily tadalafil |
|---|---|
| Fewer total pills, and less medication on days you don't need it | No timing at all, which many couples find more natural |
| Requires some planning | Takes about 5 days of daily use to reach a steady level |
| Any of the four drugs | Also treats BPH urinary symptoms |
Cost can cut either way, depending on how often you'd use the as-needed dose. Your prescriber and pharmacist can help compare.
How men and doctors choose
Head-to-head studies haven't shown one drug to be clearly more effective than the others at equivalent doses. The choice usually comes down to:
- Timing and spontaneity, the main reason men pick tadalafil.
- Side effects. A man who gets back aches on tadalafil may do better on sildenafil, and vice versa for vision changes.
- Other conditions and medications, like BPH, heart rhythm issues, or drugs that raise PDE5 inhibitor levels.
- Price and insurance coverage. Generic sildenafil and tadalafil are usually the cheapest.
If one doesn't work after several proper tries, switching to another or adjusting the dose with your prescriber is common and reasonable.
Rules that apply to all four
- Prescription only in the United States.
- No more than one dose in 24 hours for as-needed use, and don't take two different PDE5 inhibitors together.
- Sexual stimulation is still required.
- Never with nitrates or riociguat. Full safety guide →