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Alcohol and marijuana have very different health effects -- here's which is worse, according to science

Erin Brodwin

Which is worse for you: weed or whiskey?

It's a tough call. There are dozens of factors to account for, including how the substances affect your heart, brain, and behaviour, and how likely you are to get hooked. Time is important, too -- while some effects are noticeable immediately, others only begin to shape up after months or years of use.

The comparison is slightly unfair for another reason: While scientists have been researching the effects of alcohol for decades, the science of cannabis is a lot murkier due to its mostly illegal status.

Still, based on the studies we have, there appears to be a clear winner.

30,722 Americans died from alcohol-induced causes in 2014. There have been 0 documented deaths from marijuana use alone.

Last year, more than 30,000 people died from alcohol-induced causes in the US -- and that does not count drinking-related accidents or homicides. If those deaths were included, the number would be closer to 90,000, according to the CDC.

Meanwhile, no deaths from marijuana overdoses have been reported, according to the DEA. A 16-year study of more than 65,000 Americans published in the American Journal of Public Health found that the healthy marijuana users were not more likely to die of an early death than the healthy men and women who did not use cannabis.

Marijuana appears to be significantly less addictive than alcohol.

Close to half of all adults have tried marijuana at least once, making it one of the most widely used illegal drugs. Yet research suggests that a relatively small percentage of people become addicted. For a large 1994 survey, epidemiologists at the National Institute on Drug Abuse asked more than 8,000 people between the ages of 15 and 64 about their drug use. Of those who had tried marijuana at least once, roughly 9% eventually fit a diagnosis of addiction. For alcohol, the figure was about 15%. To put that in perspective, the addiction rate for cocaine was 17%, while heroin was 23% and nicotine was 32%.

Marijuana may be harder on your heart; while moderate drinking could be beneficial.

Unlike alcohol, which slows down your heart rate, marijuana speeds it up, which could have negative short-term effects on the heart. Still, the largest-ever report on cannabis from the National Academies of Sciences, which was released in January, found insufficient evidence to support or refute the idea that cannabis might increase the overall risk of a heart attack.

On the other hand, low to moderate drinking -- about a glass a day -- has been linked with a lower risk of heart attack and stroke when compared to complete abstention. Still, James Nicholls, a director at Alcohol Research UK, told the Guardian that those findings should be taken with a grain of salt since 'any protective effects tend to be cancelled out by even occasional bouts of heavier drinking.'

Alcohol is strongly linked with several types of cancer; marijuana is not.

In November, a group of the nation's top cancer doctors issued a statement asking people to drink less. They cited strong evidence that drinking alcohol -- as little as a glass of wine or beer per day -- increases the risk of developing both pre- and postmenopausal breast cancer. The US Department of Health lists alcohol as a known human carcinogen. Research highlighted by the National Cancer Institute suggests that the more alcohol you drink -- particularly the more you drink regularly -- the higher your risk of developing cancer.

For marijuana, some evidence initially suggested a link between smoking and lung cancer, but that hs been debunked. The large January report found that cannabis is not connected to any increased risk of the lung cancers or head and neck cancers tied to smoking cigarettes.

Both drugs may be linked with risks while driving, but alcohol is worse.

A research note published by the National Highway Traffic Safety Administration concluded that having a detectable amount of THC (the main psychoactive ingredient in cannabis) in your blood did not increase the risk of car accidents. Having a blood-alcohol level of 0.05% or higher increased the chances of being in a crash by 575%.

Still, combining the two appears to have the worst results. 'The risk from driving under the influence of both alcohol and cannabis is greater than the risk of driving under the influence of either alone,' the authors of a 2009 review wrote in the American Journal of Addiction.

Several studies link alcohol with violence, particularly at home. That has not been found for cannabis.

It's impossible to say whether drinking alcohol or using marijuana causes violence, but several studies suggest a link between alcohol and violent behaviour. According to the National Council on Alcoholism and Drug Dependence, alcohol is a factor in 40% of all violent crimes, and a study of college students found that the rates of mental and physical abuse were higher on days when couples drank.

On the other hand, no such relationship appears to exist for cannabis. A recent study looked at cannabis use and intimate partner violence in the first decade of marriage, and found that marijuana users were significantly less likely to commit violence against a partner than those who did not use the drug.

Both drugs negatively impact your memory, but in different ways. These effects are the most common in heavy, frequent, or binge users.

Both weed and alcohol temporarily impair memory while they are being used, and alcohol can cause blackouts by rendering the brain incapable of forming memories. In terms of their long-term effects, the most severe impacts are seen in heavy, chronic, or binge users who begin using in their teens.

For marijuana, studies have shown that these effects can
persist for several weeks after stopping marijuana use. There may also be a link between daily weed use and poorer verbal memory in adults who start smoking young.

Chronic drinkers display reductions in memory, attention, and planning as well as impaired emotional processes and social cognition -- and these can persist even after years of abstinence.

Both drugs are linked with an increased risk of psychiatric disease. For weed users, psychosis and schizophrenia are the main concern; with booze, it's depression and anxiety.

The largest existing review of marijuana studies found substantial evidence of an increased risk among frequent marijuana users of developing schizophrenia -- something that studies have shown is a particular concern for people at risk of getting the disease in the first place. Weed can also trigger temporary feelings of paranoia and hostility, but it's not yet clear if those symptoms are linked with an increased risk of long-term psychosis.

On the other hand, self-harm and suicide are much more common among people who binge drink or drink too frequently. But scientists have had a hard time deciphering whether excessive alcohol use causes depression and anxiety or whether people with depression and anxiety drink in an attempt to relieve those symptoms.

Alcohol appears to be linked more closely with weight gain than marijuana, despite weed's tendency to trigger the munchies.

Weed gives you the munchies. It makes you hungry, reduces the natural signals that tell you you're full, and may even temporarily make food taste better. But despite eating over 600 extra calories when smoking, marijuana users don't -- on the whole -- have higher BMIs. In fact, studies suggest that regular smokers are actually at a slightly reduced risk of obesity.

Alcohol, on the other hand, appears to be linked with weight gain. A study published in the American Journal of Preventative Medicine found that people who drank heavily had a higher risk of becoming overweight or obese. Plus, alcohol itself is caloric: A can of beer has roughly 150 calories; a glass of wine has about 120.