By Michael Woods Source: Toledo Blade Marijuana shook off its "weed-with-roots-in-hell" reputation decades ago, after scientific studies punctured old myths and challenged popular misconceptions about the drug. Folklore about marijuana dates to a classic 1936 film, Reefer Madness: Devil's Harvest. It showed marijuana causing instant addiction, a craving for heroin, crime sprees, and insanity. Newer studies gradually painted a different portrait of marijuana as a drug that rarely leads to addiction or serious crime by users. Marijuana found a niche in medicine. Although rarely used, it is a second-line drug that can relieve nausea and vomiting and certain other problems when other drugs fail. Millions of Americans have tried marijuana. A 1999 National Academy of Sciences (NAS) report estimated that one-third of the U.S. population over age 12 - 69 million people - had tried marijuana at least once. Most used marijuana for brief periods in their teens or 20s, and stopped. The growing acceptance of marijuana has fostered a new misconception, especially among younger people: That all the scientific uncertainties about marijuana's safety have been resolved. Marijuana, they believe, is a totally harmless substance persecuted by overly zealous law enforcement officials. In reality, serious scientific questions about marijuana's effects and safety remain unanswered. They extend beyond possible health problems from inhaling marijuana smoke into the lungs. As NAS noted, marijuana smoke, like tobacco smoke, contains carcinogens and other harmful chemicals. Inhale smoke containing those substances, and the toxic materials go into the blood and circulate throughout the body. One of the most serious unanswered questions involves marijuana's effects on brain cells. Here's the situation: Marijuana interferes with the normal workings of brain cells. That's why marijuana produces its "high" and causes changes in the way a user thinks and senses the world. Computerized brain images of heavy marijuana users show different patterns of blood flow and nerve cell activity. Psychological tests of long-term users also show unusual problems with "cognitive functioning." That means problems with memory, focusing attention, performing complex tasks, and other problems. A scientific debate is under way - largely hidden from public view - on the importance of those changes. Do brain cells fully recover after a person stops using marijuana, with the memory impairments disappearing? Or does marijuana have a toxic effect on nerve cells that slowly causes lasting damage that worsens after years of use? Studies in animals reinforce the concerns. They show that marijuana's active ingredient alters the activity of a brain system critical for normal memory. Experts agree that cognitive changes last for hours or days after a person uses marijuana. But they disagree on whether those problems last longer and grow worse over time. The disagreements are sharp, and one study may reach conclusions exactly the opposite of another. Early in March, for example, an international research group reported that cognitive impairments do last and worsen. They studied 102 people who had used marijuana almost daily for years. "The kind of impairments observed in this study have the potential to impact academic achievements, occupational proficiency, interpersonal relationships, and daily functioning," they reported in the Journal of the American Medical Association (JAMA). Mental impairments, researchers said, develop silently and may be apparent only after 10 or 20 years of heavy marijuana use. A year earlier, equally distinguished researchers found no lasting ill effects after studying 108 heavy marijuana users. "We still must live with uncertainty," Harvard University's Dr. Robert G. Pope, Jr., summed up the situation in a JAMA editorial. Today's marijuana users will do the same - with their own long-term health at stake - as unknowing subjects in a huge, real-life experiment. Their fate will help scientists paint marijuana's final portrait. Michael Woods is the Blade's science editor. His column on health appears each Monday. Source: Blade, The (OH) Author: Michael Woods Published: March 25, 2002 Copyright: 2002 The Blade Contact: letters@theblade.com Website: http://www.toledoblade.com/