Marijuana
Lethal Dose: A comically large amount�more than a thousand times the effective dose, or about a three-pound blunt.
Addiction: Low, comparatively: about 9 percent of users, but between a quarter and a half of heavy smokers.
Weight: Routine stoners have been shown to consume 600 more calories a day, but don’t have higher BMIs, possibly because of the relationship between marijuana use, insulin, and blood sugar.
Sex: Heavy use might lower sperm count, though studies showing risk of lowering testosterone have been called into question.
Sleep: Large amounts of the cannabinoid CBD seem to induce sleep, but THC actually disrupts it. A standard joint can screw with sleep for days.
Driving: Driving with THC in your system doubles the chance of an accident, although if a frequent smoker gets pulled over while high, there’s only a 30 percent chance he’ll fail the field sobriety test.
Brain: Marijuana use is associated with a whole raft of brain problems, though in most cases the cause and effect aren’t really clear (see opposite page).
Heart: Something in pot�THC, another cannabinoid, carbon monoxide from the smoke�may increase the risk of having a heart attack immediately after smoking by five times (so does sex, a bit less dramatically).
Cancer: In terms of carcinogens, a joint is on par with a full pack of cigarettes, but the studies are ultimately inconclusive on its relationship to cancer�it possibly doubles the chances in the lung and maybe plays a role in head and neck cancers. But it might also help destroy one type of cancer in the brain and help reduce the growth of others.
Other Illnesses: Maybe because of how weed seems to affect insulin control, pot use has been linked to a lower incidence of diabetes.
Alcohol
Lethal Dose: Alcohol can kill a healthy person at ten times the effective dose. That’s roughly 20 drinks.
Addiction: About 7 percent of all Americans 18 and older suffer from alcohol abuse or dependence.
Weight: Empty calories and horrible food judgment aside, alcohol may produce more galanin, a brain chemical linked to fatty-food cravings. But studies show moderate drinkers aren’t fatter.
Sex: Seven in 10 men with alcohol dependence suffer from at least one of these, one study found: erectile dysfunction, premature ejaculation, difficulty having an orgasm, sexual-aversion disorder, or a sputtered-out libido.
Sleep: Chronic use of alcohol can lead to insomnia, disrupt natural sleep stages, and cause awakenings thanks to headaches and diaphoresis (that’s, uh, heavy sweating).
Driving: Drinking can increase chances of an accident as much as 20-fold. Intoxicated drivers both speed (thanks to alcohol’s effect on the cerebellum) and demonstrate horrible decision-making processes (thanks to a compromised frontoparietal cortex).
Brain: A connection to higher rates of major depressive disorder has been found, though it’s chicken-or-egg as far as causality. Alcohol has also been shown to drastically increase the risk of a psychotic episode�by 800 percent in men and 300 percent in women.
Heart: Chronic use can raise blood pressure and therefore increases the risk of heart failure and stroke.
Cancer: Regularly assaulting the liver, colon, and oral cavity with a liquid Group 1 carcinogen turns out to be one good way of giving them cancers of many varieties.
Other Illnesses: Brings about hepatitis and eventually cirrhosis; can also act as an irritant in the GI system, so even one beer can trigger an attack of irritable-bowel syndrome.
Cigarettes
Lethal Dose: According to one estimate, the average-size person would have to suck down four or five packs’ worth in rapid succession.
Addiction: High; 50 percent to 80 percent of all smokers are addicted (which, as an estimate, seems actually a bit low).
Weight: Notoriously helpful for weight loss.
Sex: Smokers who quit get erections five times faster than those who fail to quit.
Sleep: Addicted smokers may go through nightly overnight nicotine withdrawal, with their sleep paying the price.
Driving: Nicotine may actually increase braking speed and alertness.
Brain: Smoking �ages� the brain faster, one study shows; in older adults, it accelerates the onset of forgetfulness, inattention, and lower mental processing speed.
Heart: A veritable slew of issues: increased risk of heart disease, hardened and narrowed arteries, hypertension, blood-vessel blockage, heart attacks, and strokes.
Cancer: The cause of 90 percent of lung-cancer cases, but also contributes to cancers of the mouth, nose, throat, stomach, pancreas, and reproductive organs, among a handful of others.
Other Illnesses: Halitosis, wrinkly skin, yellowed teeth, suppressed immune system. Linked to half the country’s incidences of gum disease.