Cialis (tadalafil) helps a man get and maintain an erection by increasing blood flow to the penis. It works by relaxing the smooth muscle in blood vessel walls, making it easier for blood to fill the erectile tissue when a man is sexually aroused. The drug doesn’t cause an automatic erection on its own; sexual stimulation is still needed to trigger the process. Cialis is also prescribed to relieve urinary symptoms caused by an enlarged prostate.
How Cialis Works in the Body
During sexual arousal, the body releases a chemical messenger called cGMP that signals blood vessels in the penis to relax and widen. Normally, an enzyme called PDE5 breaks down cGMP shortly after it’s produced, which is part of the natural cycle that ends an erection. Cialis blocks PDE5 from doing its job, so cGMP builds up to higher levels and sticks around longer. The result is stronger, more sustained blood flow to the penis.
What makes this mechanism interesting is that it creates a feedback loop. As cGMP levels rise, the drug actually becomes more effective at binding to PDE5, which means it gets better at blocking the enzyme the longer it’s working. This is one reason Cialis can remain active in the body for an unusually long time compared to similar medications.
How Long the Effects Last
Cialis is often called “the weekend pill” because its effects can last up to 36 hours in most men. You take it at least 30 minutes before sexual activity, though some men find it works faster. That long window doesn’t mean you’ll have an erection for 36 hours. It means that during that period, you’ll find it easier to get an erection when you’re sexually stimulated.
The standard as-needed dose is 10 mg, with the option to adjust to 20 mg if needed. You should not take more than one tablet per day, and because the 10 mg and 20 mg doses stay active so long, daily use of those strengths isn’t recommended.
There’s also a daily option. A low dose of 2.5 mg or 5 mg taken once every day keeps a steady level of the drug in your system, so you don’t need to plan around timing. This approach works well for men who have sex frequently or who prefer spontaneity. In clinical trials, men taking a daily 5 mg dose achieved successful intercourse significantly more often than those on placebo, with results appearing as early as the second day of treatment.
Treating an Enlarged Prostate
Cialis is the only drug in its class that’s also approved to treat the urinary symptoms of benign prostatic hyperplasia (BPH), a condition where the prostate gland grows large enough to squeeze the urethra and make urination difficult. Symptoms include a weak stream, frequent urination (especially at night), and the feeling that your bladder hasn’t fully emptied.
The same muscle-relaxing mechanism that helps with erections also loosens smooth muscle in the prostate and bladder neck, easing the flow of urine. The dose for BPH is 5 mg daily. If you’re dealing with both erectile dysfunction and an enlarged prostate, a single 5 mg daily tablet can treat both conditions at once.
How Effective It Is
Cialis works for the majority of men with erectile dysfunction, though results vary depending on the underlying cause. In a randomized, placebo-controlled trial, nearly 49% of men taking 5 mg daily reported successful intercourse by the second day of treatment, compared to about 37% on placebo. The gap widened further over the course of the study as the drug reached steady levels in the body.
Men with ED caused by conditions like diabetes or cardiovascular disease still respond to Cialis, but their success rates tend to be somewhat lower than men whose ED has psychological or age-related causes. The drug does not increase sexual desire. It only helps with the physical mechanics of getting and keeping an erection once arousal is already happening.
Common Side Effects
Most side effects are mild and tied to the same blood-vessel-relaxing action that makes the drug work. Headache is the most frequently reported, followed by indigestion, back pain, muscle aches, flushing, and a stuffy or runny nose. These typically fade within a few hours as the drug’s peak effects subside. Back pain and muscle aches, when they occur, tend to show up 12 to 24 hours after taking a dose and resolve within a couple of days.
Less common effects include dizziness, blurred vision, and a drop in blood pressure that you might notice when standing up quickly. A prolonged erection lasting more than four hours (priapism) is rare but requires immediate medical attention because it can cause permanent damage to erectile tissue.
Who Should Not Take Cialis
The most important safety rule is straightforward: never combine Cialis with nitrate medications. Nitrates, commonly prescribed for chest pain (angina) in forms like nitroglycerin tablets, patches, or sprays, lower blood pressure through a similar pathway. Combining the two can cause blood pressure to plummet to dangerous levels, potentially leading to fainting, heart attack, stroke, or death.
Cialis can also amplify the blood-pressure-lowering effect of alpha-blockers and other antihypertensive medications, so dose adjustments are often necessary if you take those. The drug has not been studied in men with recent heart attacks or strokes, uncontrolled high blood pressure, heart failure, uncontrolled irregular heartbeat, severe liver disease, or certain retinal eye conditions, so it’s not recommended for those groups.
Food, Alcohol, and Absorption
One practical advantage of Cialis over some similar medications is that food doesn’t significantly affect how it’s absorbed. You can take it with or without a meal and expect it to work the same way.
Alcohol is a different story. Both Cialis and alcohol lower blood pressure, so combining them increases the chance of dizziness, lightheadedness, and flushing. Keeping alcohol intake to no more than a few drinks is a reasonable guideline. Grapefruit juice is also worth watching, as it can raise the drug’s levels in your bloodstream by interfering with the enzymes that break it down, effectively making a normal dose act like a higher one.
Daily Use vs. As-Needed Use
Choosing between daily and as-needed dosing comes down to how often you have sex and how much you value spontaneity. The as-needed approach (10 mg or 20 mg) works well if you have sex once or twice a week and don’t mind planning around a 30-minute lead time. The 36-hour window gives you a generous buffer, but you still need to think ahead.
Daily dosing (2.5 mg or 5 mg) eliminates timing concerns entirely. Because the drug is always in your system, you can respond to the moment without preparation. Daily use also provides continuous relief from enlarged prostate symptoms, making it the default choice for men dealing with both conditions. The tradeoff is taking a pill every day regardless of whether you plan to have sex, along with a slightly higher ongoing cost.