Penile injections are one of the most effective treatments for erectile dysfunction with some studies estimating a 93% success rate. This technique is reserved for patients who fail (or are unable to use) other erectile aides such as pills, pellets into the urethra, or vacuum erection devices. Self-injection is straight forward but does carry some risks, such as dizziness, penile curvature, pain and priapism (an erection lasting longer than 4 hours).
Remember that although many men utilize injections, only commercial formulations such as Edex or Caverject are FDA approved. The generic versions of medications often contain the same medicines or more potent medications and by using them you assume the risks.