Having had personal experience with this very issue I would like to respond.
Mu brother in law was alleged to be a drug user (marijuana) by the mother of the child, they have joint custody, physical and legal. The mother alleged the drug use during a visitation hearing. The information the mother presented the judge was verbal testimony offered by my brother in law's sister. My brother in law recently called CPS on his sister because she was DUI with the kids in the car. She was arrested and charged with DUI and neglect, endangerment, etc. Now this sister goes and tells the mother of the child with which whom she is friends that my brother and law smoke pot. So the mother offers this as information in court. The judge makes a court order for my brother in law to submit to random testing over the next 30 days as well as hair follicle testing (one time) as well.
My brother in law does the tests and comes up negative.
The court order is dismissed.
My brother in law walks downstairs to the clerks desk and files a lawsuit against the mother.
Anyone wanna guess what for??
In court, its not about what you know or what you think you know, its about what you can PROVE. I advise you to proceed with this very cautiously, you could easily get locked at the hip on something like this in federal court for many years.