Which is worse for you: dagga or whiskey?
It's a tough call, but based on the peer-reviewed science, there appears to be a clear answer.
Keep in mind that there are dozens of factors to account for when comparing the health effects of alcohol and dagga, 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 crop 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 murkier because of its mostly illegal status.
Here's what we know about which substance is more harmful.
A large review published in August in the medical journal The Lancet found that among people aged 15–49, alcohol use was the leading health risk factor across the globe in 2016, with 3.8% of all female deaths and 12·2% of all male deaths attributable to alcohol use.
The review looked at published data from nearly 600 studies that comprised data on 195 countries and territories between 1990 and 2016. The results showed that among people of all ages, alcohol was the seventh leading risk factor for deaths in 2016.
The more people drank across the globe, the more their risk of dying and their risk of cancer rose, the study authors found. As a result of these findings, they concluded that there was no "safe" level of alcohol consumption.
"Alcohol use is a leading risk factor for global disease burden and causes substantial health loss," the researchers wrote in their paper, "and the level of consumption that minimizes health loss is zero."
In 2014, 30,722 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 Centres for Disease Control and Prevention. Meanwhile, no deaths from marijuana overdoses have been reported, according to the Drug Enforcement Administration.
A 16-year study of more than 65,000 Americans, published in the American Journal of Public Health, found that healthy marijuana users were not more likely to die earlier than healthy people who did not use cannabis.
Cannabis is now legal in several US states.
Close to half of all US 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 1994 survey, epidemiologists at the National Institute on Drug Abuse asked more than 8,000 people from ages 15 to 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%.
Unlike alcohol, which slows your heart rate, marijuana speeds it up, which could negatively affect the heart in the short term. Still, the largest-ever report on cannabis from the US National Academies of Sciences, released in January, found insufficient evidence to support or refute the idea that cannabis may increase the overall risk of a heart attack.
On the other hand, low to moderate drinking — about one drink a day — has been linked with a lower risk of heart attack and stroke compared with abstention. 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."
In November 2017, a group of the top cancer doctors in the US issued a statement asking people to drink less. They cited strong evidence that drinking alcohol — as little as a glass of wine or beer a 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 dagga, some research initially suggested a link between smoking and lung cancer, but that has been debunked. The January report found that cannabis was not connected to any increased risk of the lung cancers or head and neck cancers tied to smoking cigarettes.
A research note published by the National Highway Traffic Safety Administration (PDF) found that, when adjusting for other factors, having a detectable amount of THC (the main psychoactive ingredient in cannabis) in your blood did not increase the risk of being involved in a car crash. Having a blood-alcohol level of at least 0.05%, on the other hand, increased that risk 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.
It's impossible to say whether drinking alcohol or using dagga causes violence, but several studies — including a recent analysis published in the journal Cognitive, Affective, and Behavioural Neuroscience — suggest a link between alcohol and violent behaviour.
For the study, which was published in January, researchers used fMRI scans to see how two alcoholic drinks impacts brain function in 50 healthy adult males. Compared with sober participants, the intoxicated volunteers were found to have reduced functioning in the prefrontal cortex, an area of the brain linked with moderating social behaviour. That reduced functioning was also linked with aggressive behaviour.
The finding aligns with some previous research on alcohol's connections with violence. 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 looking at cannabis use and intimate partner violence in the first decade of marriage found that dagga users were significantly less likely to commit violence against a partner than those who did not use the drug.
Both weed and alcohol temporarily impair memory, and alcohol can cause blackouts by rendering the brain incapable of forming memories. The most severe long-term effects are seen in heavy, chronic, or binge users who begin using in their teens.
Studies have found that these effects can persist for several weeks after stopping dagga use. There may also be a link between daily weed use and poorer verbal memory in adults who start smoking at a young age.
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.
The largest review of dagga 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 already at risk.
Weed can also trigger temporary feelings of paranoia and hostility, but it's not yet clear whether 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 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.
Weed gives you the munchies. It makes you hungry, reduces the natural signals of fullness, and may even temporarily make food taste better.
But despite eating over 600 extra calories (2,500 kilojoules) when smoking, marijuana users generally don't have higher body-mass indexes. In fact, studies suggest that regular smokers have 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 (about 600 kilojoules), and a glass of wine has about 120 (about 500 kilojoules).
When it comes to addiction profiles, risk of death or overdose, and links to cancer, car crashes, violence, and obesity, the research suggests that marijuana may be less of a health risk than alcohol. Still, because of marijuana's largely illegal status, long-term studies on all its health effects have been limited — meaning more research is needed.
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