The exact FDA-label dosing for sildenafil and tadalafil: starting doses, timing, food rules, who starts lower, and how to choose between as-needed and daily.
Both first-line ED medications are generics that work the same way and differ mainly in how long they last. Sildenafil (generic Viagra) starts at 50 mg taken as needed about an hour before sex and lasts roughly an evening. [1] Tadalafil (generic Cialis) starts at 10 mg as needed and keeps working up to 36 hours, or can be taken as a small 2.5 to 5 mg tablet every day so there is nothing to time at all. [2]
A prescription is more than a drug name, and "sildenafil 50 mg" on its own is not a plan. Below is the full dosing picture the way a provider actually writes it: dose, route, timing, maximum frequency, what moves the dose up or down, and who needs to start lower.
The standard start: sildenafil 50 mg, one tablet by mouth, as needed, about 1 hour before sexual activity. It can be taken anywhere from 30 minutes to 4 hours before. Maximum one dose per day. [1]
Adjustment: based on effect and side effects, the dose moves up to 100 mg or down to 25 mg. [1] These are the only three strengths on the label; there is no benefit to splitting toward in-between numbers.
Food and alcohol: the label allows it with or without food, but a heavy, high-fat meal slows absorption and can blunt or delay the effect, so a lighter stomach works faster. [1] Moderate alcohol did not dangerously drop blood pressure in the label's interaction study, but heavy drinking impairs erections on its own and adds to lightheadedness. [1]
Who starts at 25 mg instead: men over 65, men with liver disease such as cirrhosis, men with severe kidney impairment, men taking alpha-blockers (tamsulosin, doxazosin and similar, and only once the alpha-blocker dose is stable), and men on strong CYP3A4 inhibitors such as ketoconazole or erythromycin. [1] On ritonavir, the cap is stricter: 25 mg, and no more than one dose in 48 hours. [1]
As needed: tadalafil 10 mg, one tablet by mouth before anticipated sexual activity, maximum one dose per day. Adjust to 20 mg or down to 5 mg based on response. Do not split the tablet. [2] The effect lasts up to 36 hours, which is the practical difference: one Friday tablet can cover the weekend. [2]
Once daily: tadalafil 2.5 mg by mouth, once daily at about the same time every day, regardless of when sex happens. Increase to 5 mg if needed. [2] Daily dosing suits men who are sexually active more than about twice a week, men who hate planning, and men who also have urinary symptoms from an enlarged prostate, which tadalafil 5 mg daily is separately approved to treat. [2]
Food: no food effect. Tadalafil works the same with or without a meal. [2]
Kidney and liver limits: with moderate kidney impairment the as-needed start drops to 5 mg with a 10 mg maximum every 48 hours; with severe impairment or dialysis the ceiling is 5 mg every 72 hours and daily dosing is not recommended. With liver disease the as-needed cap is 10 mg, and severe liver disease rules it out. [2]
Neither drug is stronger than the other in any way that matters at equivalent doses; head-to-head preference studies mostly track lifestyle fit, and men switched from sildenafil to tadalafil in trials largely did fine on either. [3] Cost differences between the generics are small. What is worth paying attention to is the trial-and-adjust process, not the brand mythology.
If the adjusted dose still is not working, the next steps are real and covered in what to do when ED pills do not work. Before your first tablet, read the first-dose briefing, and know the warning signs.
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A licensed US provider reviews your health history in chat, same day, and writes the dose that fits your medications, age, kidneys, and liver rather than a one-size template. Dose adjustments afterward are part of the care, not a new fee. Message us and we confirm coverage in your state. The full process is in how to get an ED prescription online.
Reviewed by PA Michael Rubio, US Medical Director
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