There are three major categories that the warning signs of substance abuse can be placed into: physical, behavioral, and psychological.
Physical Signs
Physical clues include bloodshot eyes, large pupils, frequent nosebleeds, seizures, injuries or accidents without an alibi, poor hygiene, shakes and tremors, slurred speech, changes in sleep and eating habits, and sudden weight gain or loss.
Behavioral Signs
Behavioral shifts include poor attendance to work and school, loss of interest in activities, unexplainable need for money, silent and withdrawn demeanor towards family and friends, change in relationships and friend groups, frequently getting into trouble, and mood swings.
Psychological Signs
Psychological cues include a change in attitude, sudden mood changes, irritability, outbursts, lack of motivation, inability to focus, lethargic, withdrawn from family and friends, paranoia without reason, and periods of unusual agitation or hyperactivity.