Who this guide is for
This guide is for men who have been recommended sildenafil (Viagra) or tadalafil (Cialis) for erectile dysfunction and want to get the most from them. It is also for men who tried one of them once or twice, felt it “did not work” and are wondering whether to give up.
Many men who think these medicines failed were actually taking them in a way that worked against them: right after a big meal, too close to sex, without enough arousal or only once. The American Urological Association guideline asks clinicians to give clear instructions to get the full benefit and to adjust the dose until it works well. This guide covers the instructions part. Dose changes stay with your provider.
How these medicines work, and why arousal still matters
Sildenafil and tadalafil both block an enzyme called PDE5. That lets the blood vessels in the penis relax and fill more easily when nerves signal arousal. They do not create desire, and they do not cause an erection on their own.
The tadalafil label is direct about this: because sexual stimulation is needed to start the chemical signal, blocking PDE5 has no effect without it. MedlinePlus describes sildenafil the same way, as increasing blood flow during sexual stimulation. In practice, that means taking the tablet and then waiting for something to happen will usually disappoint. Touch, foreplay and a relaxed setting are part of how the medicine works.
Anxiety works against arousal. If worry about whether the pill will work is the main thing on your mind, the result may be weaker. Our page on performance anxiety and ED explains why.
Timing: how long each takes to work
The two medicines differ most in timing.
| Sildenafil (Viagra) | Tadalafil (Cialis) | |
|---|---|---|
| When to take it | About 1 hour before sex; anywhere from 30 minutes to 4 hours | At least 30 minutes before sex |
| Time to peak level (fasting) | 30 to 120 minutes, median 60 | 30 minutes to 6 hours, median 2 hours |
| Effect of a heavy, fatty meal | Slower to work | No effect on absorption |
| How long the window lasts | Shorter than tadalafil | Up to 36 hours |
| How often | No more than once a day | No more than once a day |
According to MedlinePlus, the ideal time to take sildenafil is about one hour before sexual activity, though it can be taken anywhere from four hours to 30 minutes beforehand. MedlinePlus on tadalafil says it is usually taken at least 30 minutes before. The CIALIS label adds that as-needed tadalafil improved erectile function compared with placebo for up to 36 hours after a dose, which is why it is sometimes called the weekend pill. Our pages on how long Cialis lasts and our sildenafil and tadalafil comparison go further.
Food: why a heavy meal slows sildenafil but not tadalafil
This is the most common reason sildenafil seems not to work. The VIAGRA label reports that taking it with a high-fat meal delays the time to peak level by about 60 minutes and lowers the peak by about 29%. The patient section of the same label gives a cheeseburger and fries as an example of a meal that can make it take longer to start working.
Tadalafil behaves differently. The CIALIS label states that the rate and extent of absorption are not influenced by food. You can take it with dinner without changing how well it works.
Practical steps for sildenafil:
- Take it on an empty stomach or after a light meal, about an hour before you expect to be intimate.
- If dinner is part of the evening, keep it lighter on fat, or take the tablet well before you eat.
- If you have eaten a heavy meal, allow extra time before judging the effect.
Our page on taking Viagra on an empty stomach covers more scenarios.
Give each dose a fair trial
One attempt tells you very little. Stress, fatigue, alcohol, a big meal or a new partner can each blunt the effect on any given night. Before deciding a medicine or dose does not work, try it on several separate occasions, with the timing and food rules above.
Keep a short record each time:
- Date and time you took the tablet
- What and when you last ate
- How much alcohol you had
- How long until you were intimate
- Firmness and how long the erection lasted
- Any side effects, such as headache, flushing or a stuffy nose
Then bring that record to your provider. The AUA guideline calls for the dose to be adjusted for optimal effect, and that is the provider’s job, not something to do by doubling up at home. If the record shows a fair trial with the right technique and the medicine still falls short, there are other options; our page on when ED pills are not working and our ED treatment roadmap explain them.
Grapefruit and some medicines matter too. Both MedlinePlus pages advise talking to your doctor about grapefruit and grapefruit juice, which can change how these medicines are processed, and certain antibiotics, antifungals and HIV medicines can raise their levels. Bring a full medicine list to every visit so your provider can check.
Alcohol deserves a special note. MedlinePlus warns that large amounts of alcohol with tadalafil raise the risk of dizziness, headache, a fast heartbeat and low blood pressure. Our page on alcohol with ED pills has more.
Safety: what to watch for, and when to call
Never combine these medicines with nitrates, including nitroglycerin for chest pain and recreational “poppers.” Together they can drop blood pressure dangerously. Our page on ED pills and nitrates explains the interaction.
Call the clinic if you notice:
- headaches, flushing or indigestion that do not settle with time
- dizziness when standing, especially if you also take blood pressure medicines or alpha-blockers
- no improvement after several fair attempts
Stop the medicine and get urgent care for:
- sudden loss or decrease of vision in one or both eyes
- sudden decrease or loss of hearing, sometimes with ringing or dizziness
MedlinePlus advises calling your doctor immediately and taking no more doses if either of these happens.
Call 911 or go to the ER for:
- chest pain during or after sex. Tell the responders you took sildenafil or tadalafil and when. The CIALIS label says at least 48 hours should pass after a tadalafil dose before nitrates are considered in a life-threatening situation, so this information changes your treatment.
- an erection lasting more than four hours
- fainting, or swelling of the face, lips or throat
How Ultimate Male gets these medicines right
At our San Gabriel and Downey clinics, oral ED medicines are recommended after an evaluation, not handed out on request. A PA-C or MD reviews your heart health, blood pressure, current medicines and labs, then explains how and when to take the medicine that fits you. Follow-up is built in, so a weak first result leads to a conversation about timing, dose or a different option rather than a dead end.
Pills are only one part of the menu, which also includes topical options, compounded Trimix and Quadmix, and the Olympus Male blend. To see them all, visit our page on ED medications, or read more about sildenafil and daily versus as-needed tadalafil.
