1. Judge your child's mood
Think about why you are concerned about your child. Do they seem to be feeling differently? Have they had unexplained changes in mood? Maybe it seems like your child is acting fearful for no clear reason. It is possible that it could be marijuana use. Marijuana is a psychoactive substance; it interacts with the user's brain, temporarily changing the way he or she thinks and feels
2. Look for changes in behavior
Smoking marijuana can cause cognitive impairment during a high which increases as more marijuana is consumed. If you think your child may be high, look for the following mental symptoms:[2][3]
Slowed reaction time
Impaired decision-making
Diminished memory
A tendency to "space out" or lose the thread of conversations
Paranoia or irrational beliefs that one is in danger. This symptom may be more common among users with existing psychiatric problems or a predisposition to them.[4][5]
3. Look for red eyes
If you really think that your child is smoking pot, it is time to start actively looking for evidence. Red eyes are one of marijuana's most notorious side-effects.[9] Marijuana sometimes gives a reddish or reddish-yellow cast to the whites of a user's eyes. This happens because marijuana may cause the capillaries in the eyes to dilate.[10]It's also possible for marijuana smoke to irritate a user's eyes and cause redness, though marijuana doesn't have to be smoked to cause eye redness. Remember not to jump to conclusions. Did your child stay up too late last night studying (or playing video games)? That could easily cause red eyes.