It's pretty simple. Since you have do mandatory drug testing to have a job, the same should apply for unemployment/welfare as well.
Testing would be every 3 months and also at random intervals occurring no more frequent than every 3 weeks. This also ensures if someone has been on drugs that the drugs will not have passed out of their system.
Anyone who fails a drug test will immediately lose all welfare benefits and not be eligible for benefits for 6 months first offense, 12 months second offense, and a lifetime ineligibilty after a third offense.