Publication Highlights:

Marijuana remains the most abused illegal substance among youth. By the time they graduate high school, about 46 percent of U.S. teens will have tried marijuana at least once in their lifetime. Although use among teens dropped dramatically in the previous decade (to a prevalence of about 12.4 percent for past-month use in 2007), adolescent marijuana use is again on the upswing. In 2013, nearly 23 percent of high school seniors were current marijuana users, and 6.5 percent used marijuana daily.

If your child is using marijuana, he or she might:

• seem unusually giggly and/or uncoordinated
• have very red, bloodshot eyes or frequently use eye drops
• have a hard time remembering things that just happened
• have drugs or drug paraphernalia, including pipes and rolling papers (perhaps claiming they belong to a friend, if confronted)
• have strangely smelling clothes or bedroom
• use incense and other deodorizers
• wear clothing or jewelry or have posters that promote drug use
• have unexplained lack of money or a surplus of cash on hand

http://www.drugabuse.gov/publications/marijuana-facts-parents-need-to-know/want-to-know-more-some-faqs-about-marijuana