A 5 mg dose of Cialis (tadalafil) can improve erectile function for up to 36 hours after you take it. That’s dramatically longer than other erectile dysfunction medications, which typically wear off in 4 to 6 hours. The 5 mg dose is also the strength prescribed for daily use, and when taken every day it maintains a steady level in your body so timing around sexual activity becomes irrelevant.
How the 36-Hour Window Works
Tadalafil has an average half-life of 17.5 hours in healthy adults. That means roughly half the drug is still active in your bloodstream nearly 18 hours after you swallow it. By the 36-hour mark, enough of the medication remains to support an erection when you’re sexually aroused, though the effect gradually weakens as the drug clears your system.
This doesn’t mean you’ll have an erection for 36 hours. Tadalafil works by relaxing blood vessels in the penis so blood flows in more easily when you’re aroused. Without arousal, nothing happens. The 36-hour window simply means the drug is available to help during that time if the moment arises.
You should take it at least 30 minutes before sexual activity. Most men notice the effects within 30 to 60 minutes, though some report it working a bit sooner.
As-Needed vs. Daily Use
The 5 mg dose serves two distinct purposes depending on how it’s prescribed. When taken as needed, a single 5 mg tablet provides that 36-hour window. When prescribed for daily use, you take 5 mg at the same time every day regardless of when you plan to have sex.
Daily dosing builds a continuous level of the drug in your system. After a few days, you don’t need to plan around the pill at all because there’s always enough tadalafil circulating to support erectile function whenever you need it. This approach is often preferred by men who have sex more than twice a week or who want the spontaneity of not thinking about timing. Daily 5 mg dosing is also the regimen used for treating enlarged prostate symptoms alongside ED.
What Affects How Long It Lasts
Several factors can shorten or extend the drug’s effective window in your body.
Age: Men 65 and older clear tadalafil more slowly. In studies, healthy older adults had a half-life of about 22 hours compared to 16 to 17 hours in younger men, resulting in roughly 25% higher drug exposure. In practical terms, the medication stays active longer if you’re older.
Other medications: Certain drugs slow the liver enzyme responsible for breaking down tadalafil. Antifungal medications like ketoconazole are the most studied example. When ketoconazole was given alongside tadalafil, the half-life nearly doubled, jumping from about 16 hours to over 30 hours, and total drug exposure more than doubled. Other medications that use the same liver pathway, including some antibiotics and HIV treatments, can have a similar effect. On the flip side, drugs like rifampin (used for tuberculosis) speed up the enzyme and can reduce tadalafil’s effectiveness.
Liver and kidney function: Both organs play a role in clearing the drug. If either is compromised, tadalafil stays in your system longer and at higher concentrations, which can increase both effects and side effects.
Food: Unlike some other ED medications, tadalafil absorption isn’t significantly affected by meals. You can take it with or without food and expect roughly the same timeline.
Alcohol and Blood Pressure Effects
Tadalafil lowers blood pressure slightly on its own because it relaxes blood vessels. Alcohol does the same thing. Combining the two can amplify that drop, particularly when you stand up quickly. In clinical studies using higher doses (10 mg and 20 mg), men who consumed the equivalent of about six drinks showed clinically significant blood pressure drops, dizziness, and lightheadedness more often than those who drank without taking the medication.
At lower alcohol amounts (around four drinks), those effects largely disappeared. While the 5 mg dose is lower than what was tested, the interaction still applies. A drink or two is unlikely to cause problems, but heavy drinking within that 36-hour window increases the chance of feeling dizzy or faint.
How Long It Takes for BPH Symptoms
If you’re taking daily 5 mg tadalafil for an enlarged prostate (BPH), the timeline for symptom relief is different from ED. Erectile function improvements can be noticeable within a few days of starting daily dosing, but urinary symptoms like frequent urination, weak stream, and nighttime bathroom trips take longer to respond.
In a large clinical trial of over 1,000 men, daily 5 mg tadalafil improved urinary symptom scores by an average of 2.6 points more than placebo after 12 weeks. Most of the benefit appeared within those first 12 weeks, with smaller additional gains continuing up to a year. So while ED effects are essentially immediate once the drug reaches steady levels, BPH relief is a slower process measured in weeks rather than hours.
How 5 mg Compares to Higher Doses
Tadalafil also comes in 10 mg and 20 mg doses, but those are only used as-needed, not daily. All three doses share the same 36-hour activity window because the half-life doesn’t change with dose. What changes is the intensity of the effect and the likelihood of side effects like headache, muscle aches, or nasal congestion. The 5 mg dose produces fewer side effects because less drug is circulating at any given time, which is one reason it’s the standard choice for daily use.
For men who find 5 mg insufficient on an as-needed basis, moving to 10 mg or 20 mg increases the peak drug level without extending the duration. The clock still runs about 36 hours either way.