Here's a good idea. Either put contraceptive into prescribed methadone or link the contraceptive regime to the methadone administration.
The Scotsman reports;
"Why are we in a situation where so many who are addicted to drugs are having children? As a first step, we should explore putting some form of oral contraception in methadone or using other methods. In that way we could reduce these problems and prevent some of these children coming into harm" - Duncan McNeil, Labour MSP for Greenock and Inverclyde
As long as the addict consents I can't see a problem.