Answer:
Probably Hair
Step-by-step explanation:
First of all, Forensic scientist would probably have to take a blood test on a human who has/done drugs
Another reason is because forensic scientist would take a sample of their sample
Lastly, Skin cells would be tested since they would check your fingerprints or something in the human body
Your hair not really since that would be in crime cases or something like that
anyways hopefully this helped