No scientific evidence indicates that marijuana improves hearing, eyesight, and skin sensitivity. Marijuana use increases the heart rate as much as 50 percent, depending on the amount of THC. It can cause chest pain in people who have a poor blood supply to the heart - and it produces these effects more rapidly than tobacco smoke does.
Scientists believe that marijuana can be especially harmful to the lungs because users often inhale the unfiltered smoke deeply and hold it in their lungs as long as possible. Therefore, the smoke is in contact with lung tissues for long periods of time, which irritates the lungs and damages the way they work. Marijuana smoke contains some of the same ingredients in tobacco smoke that can cause emphysema and cancer. In addition, many marijuana users also smoke cigarettes; the combined effect of smoking these two substances creates an increased health risk.
"Burnout" is a term first used by marijuana smokers themselves to describe the effect of prolonged use. Young people who smoke marijuana heavily over long periods of time can become dull, slow moving, and inattentive. These "burned-out" users are sometimes so unaware of their surroundings that they do not respond when friends speak to them, and they do not realize they have a problem.
Laboratory studies have shown that animals exhibit symptoms of drug withdrawal after cessation of prolonged marijuana administration. Some human studies have also demonstrated withdrawal symptoms such as irritability, stomach pain, aggression, and anxiety after cessation of oral administration of tetrahydrocannabinol (THC), marijuana's principal psychoactive component. Now, NIDA-supported researchers at McLean Hospital in Belmont, Massachusetts, and Columbia University in New York City have shown that individuals who regularly smoke marijuana experience withdrawal symptoms after they stop smoking the drug.
Studies at Columbia University in New York City have demonstrated that, in...