Firmly believe in the stick and carrot approach in this.
Stick: Drug and Alcohol testing of safety critical crew at random.
Carrot: before the stick is introduced have an established D and A treatment programme (Your airline in partnership with their private health care provider and if they don't have one make them get one) that someone with a problem can self refer without your airline getting involved or if you "fess up" to the airline also get referred and get to keep their job once treatment is complete.
Forcing people into the underground with this one is not what EASA wants. If they're serious about treating mental health then they should be forced to develop treatment programmes for all mental health issues.