I should clarify that in some types of RE drug treatment may not work.
For RE caused by Traumatic Masturbation Syndrome, mastubatory re-conditioning is the only known cure.
For RE caused by chronic masturbation and/or heavy pornography use, stopping all masturbation and porn watching, combined with psychotherapy is the treatment of choice.
If the chronic masturbation and porn use is diagnosed as an obsessive compulsive disorder, sometimes a drug combination therapy of an SSRI antidepressent and Wellbutrin (to counter the SSRI's sexual side effect of RE ---yes it IS ironic) will be prescribed
For low RE caused by low arousal levels due to lack of sexual attraction to the partner or sexual boredom, marital therapy can sometimes help but of all the causes of RE this is the hardest one to cure.
Drugs are most effective when the RE is caused by performance or other types of anxiety, which is the most common cause of RE.