Medications can be injected directly into the corpora cavernosa to attain and maintain erections. Medications such as papaverine hydrochloride, phentolamine, and prostaglandin E1 can be used alone or in combinations to attain erections. Combining small amounts of each drug is preferred over using a single drug because of increased efficacy and fewer side effects. Even though such injections can be effective, they are not widely used because the injections are painful, there may be scarring of the penis, and there is a risk of developing priapism.