Child custody is based on what is in the best interest of the child. The court uses a list of statutory factors to aid them in arriving at that determination.
Evidence of your wife's alcohol and drug use is certainly a factor in determining the custody. Also, you yourself may give testimony as to what you have seen. That is not irrelevant, nor is it excluded as opinion or hearsay. If you have other documents, you should have them reviewed by an attorney as there are procedures that must be followed to have them received as evidence.
Contact an attorney in your area for advice on how to proceed.
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In all custody cases the Court will determine custody based on the best interests of the child. If she was awarded custody earlier you will need to show a major material change since custody was awarded or agreed upon.
The issues you raise appear to be major and should be brought up in Court. The alcohol and drug abuses are serious and the Court will be very concerned with that type of home environment and parental behavior.
You definitely need to consult with an experienced custody attorney in your area, who will advise you on the best Court strategy. I don't see any negative consequences of bringing the evidence up.