Cialis (tadalafil) is a prescription medication that helps men get and maintain erections by increasing blood flow to the penis. It works for up to 36 hours after a single dose, which is significantly longer than similar medications. Beyond erectile dysfunction, Cialis is also approved to treat symptoms of an enlarged prostate.
How Cialis Works in the Body
During sexual arousal, your body releases a signaling molecule called nitric oxide in the blood vessels of the penis. This triggers the production of a chemical messenger (cGMP) that tells smooth muscle cells in the vessel walls to relax. When those muscles relax, the blood vessels widen and more blood flows in, producing an erection.
Normally, an enzyme called PDE5 breaks down that chemical messenger fairly quickly, which is part of why erections naturally subside. Cialis blocks PDE5 from doing its job, so the messenger accumulates and the smooth muscle stays relaxed longer. The result is stronger, more sustained blood flow when you’re aroused. This is an important distinction: Cialis doesn’t create arousal on its own. It amplifies the body’s existing response to sexual stimulation.
Erectile Dysfunction
Cialis was first approved in 2003 for erectile dysfunction and remains one of the most widely prescribed treatments. It comes in two dosing approaches. The as-needed option is a 10 mg tablet taken about 30 minutes before sexual activity, no more than once a day. The daily option is a smaller 2.5 mg tablet taken at the same time each day, regardless of when you plan to have sex. Your prescriber may adjust either dose based on how well it works and how you tolerate it.
The daily approach suits men who have sex more than twice a week or who prefer spontaneity without planning around a pill. The as-needed approach works well for less frequent sexual activity. Clinical trials showed that Cialis improved erectile function compared to placebo for up to 36 hours after a single dose, a window that earned it the nickname “the weekend pill.”
Enlarged Prostate Symptoms
Cialis is also approved to treat the urinary symptoms that come with benign prostatic hyperplasia (BPH), a condition where the prostate gland gradually enlarges and presses on the urethra. Men with BPH often experience a weak urine stream, difficulty starting urination, frequent trips to the bathroom, and the feeling that the bladder hasn’t fully emptied.
The same PDE5-blocking mechanism that helps with erections also relaxes smooth muscle in the prostate, bladder neck, and urethra. This eases the physical squeeze on the urinary tract. Cialis also appears to improve blood flow to these tissues, reducing the inflammation and oxygen deprivation that contribute to symptoms over time. Animal studies suggest it may even calm overactive nerve signals in the lower urinary tract, which helps with the urgency and frequency side of BPH. For men dealing with both ED and BPH, the daily 5 mg dose can treat both conditions with a single pill.
How Long It Lasts
Tadalafil has a half-life of about 17.5 hours, meaning half the drug is still active in your bloodstream nearly a full day after you take it. That translates to a clinically effective window of up to 36 hours. By comparison, sildenafil (Viagra) lasts roughly 4 to 6 hours.
This long duration is Cialis’s main practical advantage. You don’t need to time the pill precisely before sex, and the effects can span from one evening well into the next day. Another difference from sildenafil: tadalafil absorption isn’t significantly affected by food or alcohol, so you don’t need to take it on an empty stomach or skip a glass of wine at dinner.
Common Side Effects
Most side effects are mild and stem from 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. Back pain and muscle aches are somewhat unique to Cialis among ED medications and typically show up 12 to 24 hours after taking a dose, then resolve within a couple of days.
These side effects tend to be less noticeable at lower daily doses compared to the higher as-needed dose. For most men, they diminish after taking the medication a few times as the body adjusts.
Who Should Not Take Cialis
The most important safety concern is the interaction with nitrate medications, which are commonly prescribed for chest pain (angina). Nitrates work by boosting the same cGMP pathway that Cialis amplifies. Taking both at the same time can cause a dangerous drop in blood pressure. In studies, combining tadalafil with nitroglycerin caused standing systolic blood pressure to fall below 85 mmHg in significantly more people than nitroglycerin alone, with effects persisting up to 24 hours after the Cialis dose. Diastolic pressure dropped more than 20 points in some cases.
This interaction isn’t limited to prescription nitrates. Recreational drugs like amyl nitrite (“poppers”) carry the same risk. If you take any form of nitrate, Cialis is not safe for you. Men on alpha-blockers for blood pressure or prostate symptoms should also discuss timing and dosing carefully with their prescriber, since both drug classes lower blood pressure through overlapping pathways.