Talk to your parents about it. You're not her parent, and your parents will be able to discuss it with her in a rational, mature fashion.
Angry outbursts, mood swings, irritability, manic behavior, or overall attitude change
Talking incoherently or making inappropriate remarks
Risky behavior, such as driving under the influence of drugs, starting a fight, or engaging in unprotected sex
Secretive or suspicious behavior: frequent trips to the restroom, basement, or other isolated areas for privacy while using drugs
Deterioration of physical appearance and grooming
Wearing sunglasses and/or long-sleeved shirts frequently or at inappropriate times Frequent absences from work or school; drop-off in quality of work or grades
Neglect of family responsibilities
Evidence of money problems: frequent borrowing, selling possessions, or stealing items from employer, home, or school
Legal problems rooted in drug use: arrest for driving under the influence, possession of a controlled substance, disorderly conduct, or stealing
if any two of these are there,u can suspect a drug abuse...My dad wont let my sister move, what should she do?