Other uses for this medicine This medication may be prescribed for other uses; ask your doctor or pharmacist for more information. Effects may last up to 36 hours. These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects. This boosts blood flow and helps you get an erection from sexual activity. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. It works for up to 36 hours.How Cialis Works. Tadalafil and other PDE5 inhibitors primarily work by inducing muscle relaxation. Tadalafil stops the breakdown of a chemical responsible for relaxing muscles. In ED and PAH, the drug targets muscle cells in blood vessels. When the blood vessel muscle cells relax, this expands the vessel and increases blood flow; this . View other PDE5 Inhibitors. Cialis (tadalafil) is an expensive drug used to treat erection problems in men. It may also be used to treat the enlargement of the prostate gland. This drug is slightly more popular than comparable drugs. It is available in both brand and generic versions. GoodRx can help you save over 97% off the average retail price of the generic version. Generic Cialis at certain pharmacies is less than $13 with a free .