A phosphodiesterase type 5 inhibitor, is used to treat erectile dysfunction (ED) and decreased libido in males. Cialez 20^TM works by aiding relaxation of blood vessels and increasing blood flow in the penis during sexual arousal, resulting in improved erectile function. Cialez 20^TM is much longer lasting than Viagrez. Effects can be felt anywhere between 36-48 hours. Tadalafil improves erectile function significantly, possibly increase testosterone through increased sexual activity, and is very safe. There are limited side effects associated with its use. The most common side effects are headache, upset stomach, back pain, and muscle aches, and usually subside with in a few hours.