Still, over the past 20 years the prevalence of marijuana use has declined. Half as many people reported current marijuana use in 2000 as 20 years earlier. And while 11 million Americans (4.8 percent) reported marijuana use in the past month in 2000, this compares with an estimated 24 million (13.2 percent) in 1979.

People age 18 to 25 are the most likely to use marijuana (13.6 percent) and people over 35 are the least likely (2.3 percent). Marijuana use among youth age 12 to 17 doubled from 1992 to 1995, from 3.4 percent to 8.2 percent. Since then it has declined to the 7.2 percent level.

Marijuana use among high school students increased in the 1990s, following a gradual decline that began in 1979. Marijuana use among high school seniors rose from 12 percent in 1992 to 22.4 percent in 2001. During that same time period (1992 to 2001) current use among tenth graders rose from 8 percent to 19.8 percent, and among eighth graders from 4 percent to 9.2 percent. Research finds that this increase in marijuana use among youth is associated with a decline in the belief that it is harmful and a decline in the disapproval of marijuana use.

The effects of marijuana are subtler and less noticeable than the effects of many other drugs. A person under the influence may not be as easily recognized as such, compared with someone who is drunk on alcohol, tweaking on methamphetamine, or nodding on opiates. The effects of marijuana peak within 20 minutes and last two or three hours.

Marijuana affects the parts of the brain involved in attention, memory, learning, and the integration of sensory experiences with motivation and emotions. Marijuana intoxication impairs driving skills because it diminishes reaction time, motor coordination, and the ability to maintain and shift attention. An adverse reaction to marijuana resembles a panic or anxiety attack.

Chronic marijuana use, like cigarette use, results in respiratory problems such as nagging coughs, frequent chest colds, chronic bronchitis, and increased risk of pneumonia. Scientific evidence indicates that long-term marijuana use can adversely affect the immune system and reproductive systems.

Marijuana smoke contains some of the same cancer-causing agents that are in tobacco smoke. In fact, the tar and carbon monoxide levels absorbed by marijuana smokers are three to five times greater than those absorbed by tobacco smokers. Smoking five joints per week exposes users to as many carcinogens as smoking a pack of cigarettes per day.

Both tolerance and mild withdrawal effects have been noted. THC produces the same patterns of biochemical events that reinforce dependence on other drugs such as cocaine and heroin. Cannabis abuse and cannabis dependence are diagnostic categories for substance abuse disorder defined by the American Psychiatric Association. A person is considered addicted if he or she compulsively and uncontrollably uses, craves, and seeks drugs, even in the face of repeated negative health and social consequences.

If you think that marijuana is a benign, harmless drug, then think again. The use of marijuana creates significant, detrimental consequences, especially among youth. Nationwide nearly a quarter of a million Americans (223,597) who sought addiction treatment reported marijuana as their primary substance problem in 1999. Half of these were individuals under the age of 20. The average age of first marijuana use has been estimated at 13 years. And if kids are regularly smoking marijuana (or abusing any other drug, for that matter) they are not attending to the other necessary aspects of growing up-psychologically, emotionally and cognitively.

If you think today's marijuana is the same drug you may have dabbled with in your college years 20 or 30 years ago, think again. It is not. Compared with the marijuana of decades ago, today's marijuana is a much more potent drug, the effect of which can hasten the progression from abuse to dependence. Add to the mix that it is now sometimes dipped in other substances, particularly PCP (phencyclidine) or formaldehyde, or smoked in combination with crack cocaine.

Marijuana use is not an innocent, innocuous rite of passage, but a perilous pastime that can disrupt your child's learning and developmental progression. It can and does result in addiction. Marijuana use, no matter how innocently it may begin, is a slippery slope-a risky proposition that can lead your child down the road to the dangerous and unpredictable world of drug abuse.

Carol Falkowski, director of research communications at the Hazelden Foundation, has monitored drug abuse trends at the national level for nearly two decades. She is author of the reference book, Dangerous Drugs: An Easy-to-Use Reference for Parents and Professionals, (2nd edition) Hazelden Publishing, 2003.

Published in The Voice, Summer 2003