I seriously doubt it, but depending on his age he would benefit more from a frank and understanding discussion about why he had them and what he was using them for. Remember - diclazepam is still currently regarded as a 'legal high', so although I can sympathise with any parent who finds drugs in their childrens possession, he is legally entitled to have them and may feel that his use of them is preferable to using illegal drugs.
Im not a parent so I can only begin to imagine what a nightmare you feel you are currently facing, but a careful and considered approach has to be the best way to engage him about his drug use. As for the drugs themselves, if they are actual diclazepam tablets, they are relatively safe in small doses compared to most of the 'legal highs' on sale, as they are basically the same drug as diazepam (Valium) and were originally developed and tested by the same company that invented Valium.
I wish you and your family all the best, and if you require a little extra piece of mind, it will be virtually impossible for chilldren to access drugs like this following the 6th April
Stee
