The standard recommended dose of Viagra is 50 mg, taken about one hour before sexual activity. It comes in three strengths (25 mg, 50 mg, and 100 mg), and 100 mg is the maximum you should take in a single day. Your prescriber may adjust your dose up or down from that 50 mg starting point depending on how well it works and how you tolerate it.
The Three Available Doses
Viagra tablets are manufactured in 25 mg, 50 mg, and 100 mg. Most men start at 50 mg. If that works well but causes bothersome side effects, stepping down to 25 mg is the usual next move. If 50 mg isn’t effective enough, 100 mg is the highest approved dose. You take it only when you need it, not on a daily schedule, and never more than once in a 24-hour period.
A lower starting dose of 25 mg is typically recommended for men over 65, those with significant liver problems like cirrhosis, or those with severe kidney impairment. In these groups, the body clears the drug more slowly, so a standard 50 mg dose produces higher blood levels than it would in a younger, healthier person.
When and How to Take It
The general guidance is to take Viagra roughly one hour before you plan to have sex, though the window is flexible. It can be taken anywhere from 30 minutes to 4 hours beforehand. The drug reaches its strongest effect around the 1- to 2-hour mark, and the effect gradually fades after that. By the 4-hour point, most men notice a noticeably weaker response compared to the peak.
What you eat matters. A high-fat meal eaten around the same time as the pill delays the drug’s peak effect by about an hour and reduces the peak concentration in your blood by roughly 29%. That doesn’t mean it won’t work at all, but taking it on an empty stomach or after a light meal gives you a faster, stronger response. If you’ve just had a heavy dinner, plan for a longer wait before expecting results.
Viagra also requires sexual arousal to work. It doesn’t produce an automatic erection on its own. It relaxes blood vessels in the penis so that when you’re sexually stimulated, blood flows in more easily.
Side Effects at Different Doses
Side effects are dose-dependent, meaning they become more common and more noticeable as the dose goes up. The most frequently reported ones include headache, facial flushing, nasal congestion, indigestion, and temporary changes in vision (a slight blue tint or increased light sensitivity). At 25 mg, these tend to be mild or absent for most men. At 100 mg, they’re more likely and more pronounced.
This is exactly why the 50 mg starting dose exists. It’s meant to be the sweet spot between effectiveness and tolerability. If you’re getting good results at 50 mg with few side effects, there’s no benefit to taking more.
Medications That Don’t Mix With Viagra
Viagra lowers blood pressure as part of how it works. On its own, that drop is mild. Combined with certain other drugs, it can become dangerously steep.
- Nitrates are the most critical concern. These are medications for chest pain or heart conditions, often taken as pills or sprays. Combining them with Viagra can cause a severe, potentially life-threatening drop in blood pressure. This combination is not just risky; it’s an absolute contraindication.
- Alpha-blockers, commonly prescribed for enlarged prostate or high blood pressure (brand names include Flomax, Cardura, Hytrin, and Minipress), can also cause low blood pressure when taken alongside Viagra. If you use one of these, your prescriber will likely start you at the 25 mg dose and advise separating the timing of the two medications.
- Other blood pressure medications can amplify Viagra’s blood-pressure-lowering effect. This doesn’t always rule out using it, but it means closer monitoring and possibly a lower dose.
Viagra vs. Sildenafil for Other Conditions
Sildenafil, the active ingredient in Viagra, is also sold under the brand name Revatio for treating pulmonary arterial hypertension, a type of high blood pressure in the lungs. The dosing is completely different: Revatio is taken as 20 mg three times a day, every day. Viagra for erectile dysfunction is taken as a single dose of 25 to 100 mg only when needed. These are separate prescriptions for separate conditions, and the two shouldn’t be used interchangeably.
Generic sildenafil for erectile dysfunction is widely available and uses the same 25/50/100 mg dosing as brand-name Viagra. The active ingredient and dose ranges are identical.