I can't tell you how many times I am asked this question by teenage patients, older patients, their families, my friends and colleagues. Marijuana is the most frequently used illicit drug in the United States. It's not just your imagination; its use is on the rise, especially among junior high and high school students. Among adults in the U.S., the prevalence of use has remained 4 percent since the early 1990s. The prevalence of marijuana abuse and dependence, however, has increased significantly. Risk factors for abuse and dependence include being male, Native American, widowed/separated/divorced, and living in the West.
Is Marijuana really a gateway drug and what does that mean? The "gateway" theory of development of drug abuse describes sequential stages of progression in drug involvement from adolescence into adulthood, starting with legal drugs such as alcohol or cigarettes, followed by marijuana, illicit drugs other than marijuana, and abuse of prescription drugs. The evidence for pot as a gateway drug is a mixed bag really. There are twin studies where evidence shows that when one twin uses pot before the age of 17 their odds of drug or alcohol dependence are 2-5 times higher than the twin who didn't smoke pot. A study of school-age children in Spain identified specific factors associated with onset of marijuana consumption: use of alcohol and tobacco, antisocial behavior, and low academic performance. This study supports the gateway theory, although it does not eliminate the possible existence of a common factor underlying initiation of alcohol, tobacco, and marijuana.
So the question here is whether the association is causal (ie, whether marijuana is a "gateway" drug) OR reflects shared risk factors, and that will always be debated. A large body of evidence does suggest that marijuana use appears to be the best predictor of later use of "harder drugs" like cocaine or heroin. Marijuana use also predicts later ecstasy use. My personal experience as a physician has mirrored this and my patients who use hard drugs did start with pot.
Is it true that it makes you infertile? In men, marijuana causes decreased serum testosterone levels, sperm count, and sperm motility. This may lead to decreased libido (interest in sex) and impotence. An increased risk of infertility may result from changes in semen characteristics seen with marijuana smoking.
In women, chronic pot use causes shorter menstrual cycles and increased prolactin levels which may impair fertility.
Can you have withdrawal symptoms if you stop smoking pot? Yes, if you are a chronic user you may have withdrawal symptoms after abrupt cessation. Marijuana withdrawal begins within ten hours of the last dose and consists of irritability, agitation, depression, insomnia, nausea, anorexia, and tremor. Most symptoms peak in 48 hours and last for five to seven days. Some symptoms, such as unusual dreams and irritability, can last for weeks.
Does marijuana cause lung cancer? We're not sure. Marijuana is not smoked with filters, unlike most cigarettes. Marijuana smoke contains nearly four times as much tar and 50 percent more carcinogens than tobacco.
Here is what complicates the question of smoking pot and lung cancer: marijuana users are five times more likely to smoke cigarettes than non-users. Use of nicotine and marijuana together likely enhance the harmful effects of each used independently.
It should be reassuring for pot smokers that although they are probably at increased risk for lung cancer, the magnitude of risk has not been well quantified. A review of 19 studies did NOT detect a significant association between lung cancer and marijuana use, after adjusting for tobacco smoking.
What about lung problems, will it cause lung disease? The association between tobacco smoking and chronic obstructive pulmonary disease (COPD) HAS been established. Longterm pot smoking is associated with many symptoms of obstructive pulmonary disease: airflow obstruction, chronic cough, bronchitis, and decreased exercise tolerance. Regular smokers of three to four marijuana cigarettes per day experience cough, wheeze, and sputum production and exhibit abnormalities in the lungs equivalent to those who smoke approximately 20 tobacco cigarettes per day.
Does smoking pot make you mentally dull (think Jeff Spicoli Fast Times at Ridgemont high)? Again there may be some reassurance to pot smokers on this front. The association between chronic marijuana exposure and cognitive dysfunction has been extensively studied but with varying results. A syndrome formerly known as the "amotivational syndrome," now called the "chronic cannabis syndrome," has been described in which chronic heavy users with cognitive impairment have a reduced ability to establish or attain goals in life, resulting in jobs that require less cognitive challenge or technological acuity.
In an analysis of 13 studies, long-term marijuana use did not result in deficits in seven of eight neuropsychological ability areas tested; but there was a small but significant decrement in the area of learning new information. Since then, published studies have had conflicting results and here are some highlights. One study compared cognitive function in longer term and shorter term marijuana users at a mean of 17 hours after last reported marijuana use. Deficits in memory, attention, learning and retrieval function were significantly greater among the longer-term marijuana users. Longer term marijuana users (four or more joints per week for a minimum of 10 years), tested after a minimum of 24 hours abstinence, and had impaired verbal memory skills compared to shorter term users and controls. Both longterm and shorter users showed inferior performance on psychomotor speed, attention, and executive functions compared with controls.
Why might this happen? The changes seen in memory do require the use of frontal, cerebellar, and hippocampal brain regions, all of which contain cannabinoid receptors so it would make sense they might be affected.
The evidence is fairly consistent that marijuana use results in cognitive deficits that persist for at least hours, and likely days after use of the drug. Whether these deficits persist in the long term and the effects of persistent heavy use have not been settled.