Putting addicts in jail is certainly not the answer. Harsh enforcement against drug users is one of the biggest failings of the War on Drugs. So is the ban on "soft" drugs like weed and hallucinogens, which don't have the same abuse potential.

But the majority of people serving sentences for drug crimes are there for selling drugs.

http://www.rollingstone.com/culture/lists/top-10-marijuana-m...

"About 40,000 inmates of state and federal prison have a current conviction involving marijuana, and about half of them are in for marijuana offenses alone; most of these were involved in distribution. Less than one percent are in for possession alone."

Remember that distribution of weed, while it sounds relatively harmless, is very often controlled by violent gangs. It's like getting Al Capone for evading taxes. The best solution is to legalize weed and put it in the hands of legal businesses.

Also:

http://fivethirtyeight.com/datalab/releasing-drug-offenders-...

There he shows that releasing all prisoners who are in jail with drug offenses as the most serious charge would only reduce the prison population by about 14%. This is counting both distribution AND simple possession. Not insignificant, but not the headline figure of 50% that you often hear.