Cialis (tadalafil) is FDA-approved to treat three conditions: erectile dysfunction, enlarged prostate symptoms, and pulmonary arterial hypertension. What sets it apart from similar medications is its long duration of action, staying effective for up to 36 hours after a single dose. That extended window is why it’s sometimes called “the weekend pill.”
Erectile Dysfunction
Erectile dysfunction is the most well-known use for Cialis. The drug works by relaxing blood vessels in the penis, making it easier to get and maintain an erection when you’re sexually aroused. It doesn’t create arousal on its own.
Clinical trials show strong results. At the 20 mg dose, between 72% and 91% of men reported improved erections, compared to 20% to 47% of men taking a placebo. Those improvements held up across a wide range of patient groups, including men with diabetes, heart disease, and other conditions that commonly contribute to ED.
One of the biggest practical advantages is timing. In a study of 348 men, 61% on Cialis reported successful intercourse at the 24-hour mark, and 64% still reported success at 36 hours, compared to 37% on placebo at both time points. That long window means you don’t need to time a pill right before sex, which many men find less stressful and more spontaneous than shorter-acting alternatives.
How the Two Dosing Options Work
Cialis comes in two distinct dosing approaches, and they suit different lifestyles. The as-needed option is a 10 mg or 20 mg tablet taken about 30 minutes before anticipated sexual activity, no more than once per day. This works well for men who are sexually active a few times a month and prefer to take medication only when they need it.
The daily option is a much smaller dose, typically 2.5 mg or 5 mg, taken at the same time every day regardless of when sex might happen. Because the drug has a half-life of about 17.5 hours, taking it daily builds a steady level in your system. This means you’re essentially always ready without planning around a pill. Daily dosing is also the approach used when Cialis treats both ED and enlarged prostate symptoms at the same time.
Enlarged Prostate Symptoms
Cialis is the only erectile dysfunction drug also approved to treat benign prostatic hyperplasia (BPH), a condition where the prostate gland grows large enough to squeeze the urethra and cause urinary problems. Common symptoms include a weak stream, frequent urination (especially at night), difficulty starting urination, and feeling like your bladder never fully empties.
The drug works here by relaxing smooth muscle in the prostate and bladder neck, easing the physical constriction around the urethra. In clinical trials, men taking Cialis showed significant improvement in symptom scores measuring both how often they urinated and how well they could empty their bladder, compared to placebo. The typical dose for BPH is 5 mg daily.
For men who have both ED and bothersome urinary symptoms, which is common since both conditions become more prevalent with age, a single daily Cialis tablet can address both at once. That convenience is a real advantage over taking separate medications for each problem.
Pulmonary Arterial Hypertension
Under the brand name Adcirca, tadalafil is also approved to treat pulmonary arterial hypertension (PAH), a serious condition where blood pressure in the arteries of the lungs is abnormally high. This forces the right side of the heart to work harder than it should, eventually weakening it.
The same mechanism that relaxes blood vessels in the penis also relaxes the blood vessels in the lungs, lowering pulmonary blood pressure and improving the heart’s ability to pump blood through them. The result is better exercise capacity and reduced symptoms like shortness of breath and fatigue. The dose used for PAH is significantly higher than what’s prescribed for ED or prostate symptoms.
Common Side Effects
Most side effects are mild and directly related to the drug’s blood-vessel-relaxing action throughout the body. Headache is the most frequent, affecting 11% to 15% of men. Indigestion occurs in 8% to 10%. Back pain is a somewhat unique side effect of Cialis specifically: 5% to 6% of men experience it, typically starting 12 to 24 hours after a dose and lasting up to 48 hours. These side effects tend to diminish with continued use and are generally less intense at lower daily doses than at the higher as-needed doses.
Important Safety Concerns
The most critical safety rule with Cialis is simple: never combine it with nitrate medications. Nitrates, commonly prescribed for chest pain (such as nitroglycerin), also lower blood pressure. Taken together, the two drugs can cause a dangerous, potentially life-threatening drop in blood pressure leading to cardiovascular collapse. This includes recreational use of “poppers” (amyl nitrite), which work through the same mechanism.
Alcohol amplifies the blood-pressure-lowering effect as well. Drinking while taking Cialis increases the risk of dizziness, lightheadedness, and fainting. A drink or two is generally manageable for most people, but heavy drinking combined with the drug can cause real problems. Men with a history of recent heart attack, stroke, very low blood pressure, or uncontrolled high blood pressure need careful evaluation before using Cialis at all.