Ideally, erections will last 30-60 minutes and will become more rigid if stimulation occurs. With injection treatment, high quality erections are available on demand, and they last longer than natural ones. The erection does not always disappear at orgasm or ejaculation. There are concerns with injections. The key ones are priapism, pain, dropout rate, and cost.
Priapism is the word to describe an unwanted, prolonged erection.
Injecting too much of the drug may cause an erection which lasts much longer than intended. After four hours, men should seek medical help for reversal of the erection. This is done by injecting an adrenaline-like drug into the penis. The pain from injecting is primarily from the needle puncture. Many men are frightened to think of injecting the penis with a needle.