Being a parent can be so challenging and the job is even more difficult if your teen is experimenting with alcohol and other substances.  Staying informed and being aware of signs that could signal drug use is so important.
Parents and teachers need to watch for the following signs that the American Council for Drug Education says are commonly exhibited by youth who use alcohol and other drugs.
But remember: the key is to watch for changes in the child's physical appearance, personality, attitude or behavior.
Physical Signs

• Loss of appetite, increase in appetite, any changes in eating habits, unexplained weight loss or gain. Slowed or staggering walk; poor physical coordination

• Inability to sleep, awake at unusual times, unusual laziness

• Red, watery eyes; pupils larger or small than usual; blank stare

• Cold, sweaty palms; shaking hands

• Puffy face, blushing or paleness

• Smell of substance on breath, body, or clothes

• Extreme hyperactivity; excessive talkativeness. Runny nose; hacking cough

• Needle marks on lower arms, legs, or bottom of feet

• Nausea, vomiting, or excessive sweating

• Tremors or shakes of hands, feet, or head

• Irregular heartbeat

• Behavioral Sign

• Change in overall attitude/personality with no other identifiable cause

• Changes in friends; new hangouts; sudden avoidance of old crowd; doesn't want to talk about new friends; friends are known drug users

• Change in activities or hobbies

• Drop in grades at school or performance at work; skips school or is late for school

• Change in habits at home; loss of interest in family and family activities

• Difficulty in paying attention; forgetfulness

• General lack of motivation, energy, self-esteem, "I don't care" attitude

• Sudden oversensitivity, temper tantrums, or resentful behavior

• Moodiness, irritability, or nervousness

• Silliness or giddiness

• Paranoia

• Excessive need for privacy; unreachable

• Secretive or suspicious behavior

• Car accidents

• Chronic dishonesty

• Unexplained need for money, stealing money or items

• Change in personal grooming habits

• Possession of drug paraphernalia

Drug Specific Signs
Marijuana: Glassy, red eyes; loud talking and inappropriate laughter followed by sleepiness, a sweet burnt scent; loss of interest, motivation; weight gain or loss.

Tobacco/Nicotine: Smell of tobacco; stained finger or teeth.

Alcohol: Clumsiness, difficulty walking, slurred speech; sleepiness; poor judgment; dilated pupils; possession of a false ID card.
Depressants:(including barbiturates and tranquilizers) Seems drunk as if from alcohol but without the associated odor of alcohol; difficulty concentrating; clumsiness; poor judgment; slurred speech; sleepiness; and contracted pupils.
Stimulants: Hyperactivity; euphoria; irritability; anxiety; excessive talking followed by depression or excessive sleeping at odd times; may go long periods of time without eating or sleeping; dilated pupils; weight loss; dry mouth and nose.
Inhalants: (Glues, aerosols, and vapors) Watery eyes; impaired vision; memory and thought; secretions from the nose or rashes around the nose and mouth; headaches and nausea; appearance of intoxication; drowsiness; poor muscle control; changes in appetite; anxiety; an unusual number of spray cans in the trash.