Hmmm, I know therapists have recommended handing over the credit cards with gambling addictions.
I would think in the infancy of recovery maybe it is a good idea for him to hand over his cash and cards, but if he starts begging for them, and gives you a hard time…or it goes on too long. Maybe it isn’t the best idea.
Also, he should be doing other things like counseling, meetings etc… there are reasons why he turned to drugs, and he must deal with those.
I think his loner cold turkey plan is likely to fail. I might tell him you will hold the money, but he must get additional help, and the second he bugs you about it giving him money; the deal is off.
Just my opinion.