Legal Question in Family Law in California

If the judge ordered a child custody evaluation - you should concentrate you efforts on the evaluator. Criminal records, letters from people who know her drug habit, school teachers, school records etc presented to the evaluator in a timely fashion are important. You should also be prepared to discuss the situation that led to the judge giving the mother sole legal custody - and what has changed with you since then, that make the order inappropriate now. Declarations on your behalf stating how the situation has changed since the judge granted her sole custody could help a lot. The evaluator then could ask if she were willing to take a drug test; a negative response from her could lead to an evaluator's recommendation for a switch in custody.

It would seem appropriate to request drug screening and testing to be done as part of the evaluation. Drug testing results are usually available much faster than the time it typically takes to complete a full custody evaluation. If mother tests dirty or refuses to abide by a court order to test, you should file an ex parte motion asking for custody pending the outcome of the full evaluation.