The specific medicines prescribed will vary depending upon your own particular experience of withdrawal and the symptoms you are manifesting, and it may be that certain medications will not be appropriate depending on your substance of abuse or your own personal health history; an experienced medical professional will be able to make those decisions to ensure you go through withdrawal as safely as possible.
Over time, most users need more and more of the same drug simply to achieve the same effects they experienced when consuming a lower dosage less frequently. Eventually, the user must have the drug simply to function and avoid feeling sick or terrible; this is one of the hallmarks of addiction. Stopping use of the drug often causes intense cravings, which is another symptom of withdrawal and addiction.
This is an ongoing debate in the medical community, but it is generally agreed that there is no one cause for the development of addiction. According to the National Institute on Drug Abuse, contributing factors may include a genetic predisposition to develop addictive tendencies, an environment that is permissive of drug abuse, access to illicit substances, and certain developmental issues. The existence of a Dual Diagnosis is one of the biggest risk factors for the development of addiction. Heroin Withdrawal | First Week In