How they work — and what they do not do
All four block an enzyme called PDE5. Blocking it lets a signalling molecule build up in the smooth muscle of the penile arteries, the muscle relaxes, the arteries open, and blood flows in.
The part men are most often not told: these drugs do not create an erection on their own. They amplify a signal your body has to start. You still need to be aroused and physically stimulated. A large share of the men who report a pill 'not working' took it, waited, and expected something to happen unprompted.
The other common mistake is giving up too early. Guidelines suggest trying up to eight separate attempts at the highest dose you tolerate before concluding a drug has failed. Many men try twice at a starting dose, feel embarrassed, and quit.
Which one to ask for
Sildenafil (the generic of Viagra). Works in 30 to 60 minutes, lasts around 4 to 6 hours. A heavy or fatty meal delays it considerably, so take it on a relatively empty stomach. The cheapest and most familiar option. Typical doses are 25, 50 or 100 mg.
Tadalafil (the generic of Cialis). The differentiator is duration — up to 36 hours from a single dose, which is why it picked up the nickname 'the weekend pill'. Food barely affects it. It can also be taken as a low daily dose of 2.5 or 5 mg, which removes the planning entirely and happens to help urinary symptoms from an enlarged prostate at the same time. That daily option is the one most men over 50 end up preferring.
Vardenafil (the generic of Levitra). Very similar to sildenafil in timing. Occasionally works for a man who did not respond to sildenafil, though less commonly prescribed now.
Avanafil (Stendra). The fastest of the four — often 15 to 30 minutes — and reported to cause somewhat fewer visual side effects. Still usually the most expensive, because generic supply is limited.
There is no evidence that any one of these is stronger than the others at equivalent doses. Choose on timing, side effects and price.
The nitrate warning, in plain terms
Nitrates are heart medicines that widen blood vessels: nitroglycerin tablets or spray, isosorbide mononitrate or dinitrate, and the recreational 'poppers' (amyl nitrite). ED pills widen blood vessels too. Taken together, blood pressure can crash to a level that starves the heart and brain, and people have died from this combination.
This is not a caution to weigh up. It is an absolute no. If you carry nitroglycerin for chest pain, tell any prescriber — including an online one — before you take anything on this page.
If you have taken sildenafil, vardenafil or avanafil, you must wait at least 24 hours before any nitrate. For tadalafil the wait is at least 48 hours. Carry a card or note in your wallet so emergency staff know.
Getting a dose that works
Start at a middle dose and adjust. If it half-worked, the answer is usually more drug rather than a different drug. If side effects are the problem, the answer is usually less.
Men with diabetes, men on multiple blood pressure medicines, and men who have had prostate surgery respond less often and may need the top dose. That is expected, not a sign that nothing will help.
Side effects
Common, and usually manageable
- Headache — the most frequent complaint by far
- Facial flushing and a feeling of warmth
- Blocked or runny nose
- Indigestion or reflux
- Back and muscle aches, mostly with tadalafil, usually 12–24 hours later
- A blue tinge to vision or light sensitivity, mostly with sildenafil, and temporary
Get medical help straight away
- An erection lasting more than 4 hours (priapism) — this is an emergency. Go to an emergency room; after several hours the tissue can be permanently damaged.
- Sudden loss of vision in one or both eyes — stop the drug and seek care immediately.
- Sudden hearing loss or ringing — stop and seek care.
- Chest pain during sex — do not take a nitrate. Call emergency services and tell them you have taken an ED medication.
Common questions
Are the cheap generics as good as brand-name Viagra?
Yes. Generic sildenafil contains the same active ingredient at the same dose and must meet the same FDA standards. The price difference is branding, not chemistry. Buy from a licensed pharmacy — US or otherwise verified — rather than an unregulated website.
Will I need this forever?
Not necessarily. If the cause is treatable — weight, blood sugar, a medication you are on, sleep apnoea, anxiety — men do sometimes come off them. If the cause is long-standing vascular damage, expect to keep using something.
Do they lower testosterone or cause dependence?
No to both. They do not affect hormone levels and they are not habit-forming. Some men do develop a psychological reliance — a worry that sex will not work without one — which is worth raising with a counsellor rather than ignoring.
What if it doesn't work at all?
Confirm you gave it a fair trial: highest tolerated dose, adequate stimulation, no heavy meal beforehand, several attempts. If it genuinely failed, that is useful information and points toward injections, a vacuum device, or a hormone check. It also warrants a proper vascular assessment.