The standard starting dose of Viagra (sildenafil) is 50 mg, taken about one hour before sexual activity. It comes in three tablet strengths (25 mg, 50 mg, and 100 mg), and the dose can be adjusted up or down depending on how well it works and how your body handles it. The maximum is 100 mg, and it should never be taken more than once in a 24-hour period.
How the Three Doses Compare
Viagra tablets are available in 25 mg, 50 mg, and 100 mg. Most people start at 50 mg because it balances effectiveness with a lower risk of side effects. From there, the dose is adjusted based on individual response. If 50 mg works well but causes bothersome side effects like headache or facial flushing, dropping to 25 mg often reduces those effects while still providing benefit. If 50 mg isn’t producing enough of a response, the dose can be increased to the 100 mg maximum.
Side effects tend to be dose-dependent, meaning they become more likely and more noticeable at higher doses. The most common ones are headache, flushing, nasal congestion, and temporary visual changes like a slight blue tint to vision. These are generally mild and short-lived.
Timing, Food, and How Long It Lasts
Viagra reaches its peak concentration in the blood within 30 to 120 minutes after taking it on an empty stomach, with the median being about 60 minutes. That’s why the standard advice is to take it roughly an hour before sexual activity. The effects can last up to four hours, though this varies from person to person.
One practical detail that catches people off guard: eating a high-fat meal before taking Viagra can delay its absorption by about an hour. If you’ve just had a heavy dinner, the medication will still work, but it may take noticeably longer to kick in. A lighter meal or taking it on an empty stomach gives you the most predictable timing.
Viagra also requires sexual arousal to work. It doesn’t produce an automatic erection on its own. What it does is block an enzyme that normally breaks down a signaling molecule involved in relaxing blood vessels in the penis. When you’re sexually stimulated, that signaling molecule builds up more than usual, allowing more blood flow and a firmer erection.
Lower Starting Doses for Some Groups
Adults over 65 typically start at 25 mg rather than 50 mg. The body processes the drug more slowly with age, so lower doses produce higher blood levels compared to younger adults. The same 25 mg starting point applies to people with significant liver or kidney problems, since these organs are responsible for clearing the drug from the body.
Certain medications also call for a lower starting dose. If you take alpha-blockers for an enlarged prostate or high blood pressure, a prescriber will generally start you at 25 mg to avoid a sharp drop in blood pressure when the two drugs interact.
Who Should Not Take Viagra
The most important safety rule with Viagra is that it must never be combined with nitrate medications used for chest pain (angina). Nitrates and Viagra both lower blood pressure through overlapping pathways, and taking them together can cause a sudden, dangerous drop. This applies to all forms of nitrates, including tablets, sprays, and patches. If you use nitrates in any form, Viagra is off the table entirely.
People with recent heart attacks, strokes, or severe heart failure also need careful evaluation before using the medication, because sexual activity itself places demands on the cardiovascular system.
Why 50 mg Is the Default
The 50 mg dose exists as the starting point because clinical trials showed it was effective for the majority of men while keeping side effects manageable. The option to move down to 25 mg or up to 100 mg gives room to fine-tune. In practice, many men find that 50 mg is where they stay. Others discover that 25 mg is plenty, especially if they’re older, lighter in body weight, or taking other medications that slow the drug’s metabolism.
Regardless of dose, the once-per-day limit is firm. Taking a second dose because the first one “didn’t work fast enough” is a common mistake that increases the risk of side effects, particularly headache and a prolonged drop in blood pressure. If a full 100 mg dose isn’t producing results, the issue is worth discussing with a prescriber rather than doubling up.