Cialis is the brand name for the medication tadalafil, a prescription drug used primarily to treat erectile dysfunction (ED) and the signs and symptoms of benign prostatic hyperplasia (BPH) in adult men. It is also marketed under the brand name Adcirca to treat pulmonary arterial hypertension (PAH) and improve exercise ability.

Tadalafil belongs to a class of drugs known as phosphodiesterase type 5 (PDE5) inhibitors. It works by blocking the PDE5 enzyme, which relaxes the muscles in the penis and increases blood flow to facilitate an erection during sexual stimulation. For BPH, it relaxes the muscles in the prostate and bladder to improve urine flow.

Key Characteristics
Mechanism: It is a selective inhibitor of PDE5, enhancing erectile function by increasing cyclic guanosine monophosphate (cGMP) levels.
Duration: Effects can last up to 36 hours, distinguishing it from other ED medications like Viagra.
Dosage Options: Available as as-needed doses (typically 5 mg to 20 mg taken at least 30 minutes before sexual activity) or daily low-dose versions (2.5 mg to 5 mg).
Common Side Effects: Include headache, indigestion, back pain, muscle aches, flushing, and stuffy or runny nose.
Serious Risks: Can cause a sudden drop in blood pressure if taken with nitrates (e.g., nitroglycerin); rare but serious side effects include prolonged erections (priapism), vision loss, or hearing loss.
Availability: Both brand-name Cialis and lower-cost generic tadalafil are widely available with a prescription.