Currently, medications are available to help treat addiction to opioids (like heroin), tobacco, and alcohol. Medications for other drug addictions are in development--like drugs to treat addiction to marijuana and stimulants like cocaine and meth.
One reason there aren't more drugs available is that there isn't much incentive for big pharmaceutical companies to develop them. Basically, developing addiction meds isn't worth a lot of money and isn't good PR for the drug companies. However, in response to this, the National Institute on Drug Abuse has made development of medications to treat addiction a top priority. You can read more about this on their website: http://www.drugabuse.gov/tib/MedicationsDev.html
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