It's 2:00am, the night after homecoming. Your son has been out with his date and new friends, and has just walked in. However, he is acting strange, and you suspect that he may have been using marijuana. These "new friends" don't have the best reputation around school, and he has been trying to think of ways to impress his date. Should you be worried?

How quickly does marijuana take effect? When marijuana is smoked, the effects start within minutes and peak in 10 to 30 minutes. Usually the high is over in about 3.5 hours. If marijuana is ingested (such as eating a cookie or brownie laced with marijuana) the effects are slower to peak and last for a longer period of time. By the time your son makes it home, he is likely to be coming down from his marijuana high, so many of the signs will be less pronounced. However, if you attempt to engage your son in a conversation, you are still likely to see that he is having difficulties in keeping his attention and focus.

What are the signs to look for? In addition to the signs listed below, it is important to consider the situation that your child just came from. If they have been hanging out with friends that you don't know very well or consider to be suspicious, your gut instinct may be right. Or if they are coming from a popular high school social event where there is a possibility of increased social pressures to take drugs or alcohol, this may increase the chance as well.

Bodily Signs:

  • Bloodshot eyes
  • Dry mouth
  • Smells like marijuana (sweet smell, similar to burned basil leaves)

Note: It is a myth that, when someone is high on marijuana, their pupil size increases. Research shows that even if there is a change in pupil size, the difference is so small that humans are unable to perceive it.

Behavioral Signs:

  • Responding to unusual sensations (such as tingling arms)
  • Increased appetite, especially cravings for sweets
  • Use of eye drops
  • Difficulties in thinking, comprehending, and remembering
  • Drowsiness
  • Easily distracted
  • Uncoordinated, awkward movements

Emotional Signs:

  • Elevated mood
  • Giggling or being silly
  • Lack of anxiety or stress

Verbal Signs:

  • Slowed and/or slurred responses
  • Difficulties expressing themselves coherently
  • Making comments that their sense of taste, touch, smell, sound, or vision is heightened (e.g., "Wow, this piece of pizza is the most amazing thing I have ever eaten in my entire life" or "I've never noticed how intense this pink wall color in the kitchen is").
  • Making comments that time seems to have slowed.

You will note that many of these symptoms overlap with the signs of being on other substances, such as alcohol (for example, drowsiness, uncoordinated movements, elevated mood). However, a few of the symptoms are more typical of marijuana use than alcohol use. These are: smelling like marijuana, commenting on perceptual changes, giggling, and increased appetite. These can be particularly noticeable if someone has recently used marijuana. If you suspect your child has been using marijuana, it may be best to have a conversation about it the next morning when he is thinking more clearly and able to have a real discussion with you about how frequently he is using. If you suspect that he has a chronic problem with the substance, you may want to consider seeking professional help and/or talk to his or your physician.