The medication works by relaxing the cavernosal smooth muscle cells. Injections are one of the most effective forms of ED treatment: up to 92% of patients find it effective. In a study conducted by the British Medical Journal, 88% of patients who failed to respond to PDE5-Inhibitors (Viagra, Cialis, Levitra) were successful with injection therapy. Additionally, 48% of men who failed to respond to PDE5-inhibitors responded when used in conjunction with injection therapy. According to a Continuing Medical Education (CME) Article, of the men who stop using injection therapy, 82% of them would still recommend it to a friend. 

Injection therapy treatments should not be used more than once in a 24-hour period. The most common adverse effect is priapism. Priapism is defined as a prolonged erection which lasts for more than four hours. Patients must be cautioned to call their physician if an erection persists for 4 hours or longer. Other reported side effects include hematomas, burning pain after injection, urethral damage, local infections, curvature, and prolonged erections. 

There are multiple specialty pharmacies in the US that can provide these patient specific medications.