Marijuana may be harder on your heart, while moderate drinking could be beneficial.
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 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 canceled 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 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 marijuana, 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.
Both drugs may be linked with risks while driving, but alcohol is worse.
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.