 The popular notion seems to be that marijuana is a harmless pleasure. But what are the potential adverse effects of marijuana use? That's not an easy question to answer. Most studies to date have been cross-sectional, or rely on self-reported health. Cross-sectional means a snapshot in time, so you don't know which came first. Are people sick because they're smoking marijuana? Or are they smoking marijuana because they're sick? If you just ask people how they are, pot smokers may be like, I feel great, even if they're actually suffering from some health problem. Few longitudinal studies have been done, meaning studies done over time, using objective measures of health, until now. More than 1,000 individuals followed up from birth to age 38, testing associations between cannabis use over decades, in multiple domains of physical health. They looked at 12 health outcomes, and tobacco use was associated with worse health for 8 of 12, from impaired lung function to systemic inflammation and metabolic derangements, and cannabis use was associated with just gum disease. That's it. Cannabis use was unrelated to other physical health problems. Now periodontal disease can lead to tooth loss, and there may be other dental health problems associated with smoking marijuana. But when cannabis is described as nefarious, the first thing to come to mind is probably not gingivitis. Is it possible that cannabis users are just living healthier than average lifestyles to counteract the effects of the drug, like eating more fruits and vegetables, or maybe drinking less alcohol? No, neither are pot smokers exercising anymore, and so the absence of associations between cannabis use and poor physical midlife health could not be attributed to any of these other things, so maybe marijuana is just not that bad. Heroin may increase your risk of dying, cocaine use may increase your risk of dying, but no association was found between mortality and marijuana. Now they did just follow these folks until age 38. To find out what happens after that, we need to turn to Sweden, where they recently published the longest study ever on cannabis and mortality. 50,000 men followed up to around age 60. About 30 years ago when they first reported on this cohort, no significant excess mortality was found among cannabis users or abusers, as they called them. Back then, these men were in their 30s, like in that other study. What happens when you follow them past middle age, when perhaps the health-related detrimental effects might begin to emerge? Those with a history of heavy cannabis use did end up having a significantly higher risk of death, a 40% higher risk of dying prematurely. But wait a second, I thought cannabis didn't kill, cocaine kills thousands of Americans every year, alcohol kills tens of thousands, and tobacco breaks the graph, wiping out hundreds of thousands of people in the US every year. But marijuana doesn't even make it onto the graph. But what they're referring to is that no deaths have been directly attributed to the acute physical toxicity of cannabis. So when some 19-year-old eats a cannabis cookie and then jumps off the fourth floor balcony, the direct cause of death was the fall, but that doesn't mean cannabis didn't contribute. It's true that people don't directly OD on cannabis, like you can with opiates, which can shut down your breathing. Unlike many pharmaceuticals for which a harmful dose may just be a few times larger than the prescribed dose, the therapeutic index for cannabis is like 40,000 to one. Does that mean you could smoke like 40,000 joints without ODing? No. You may be able to smoke 2 million joints before a lethal overdose. Cannabis use contributes more to disease than death, in part because people aren't injecting it. But the health-related harms of cannabis had never been quantified on a global scale until 2013. Every year, cannabis is estimated to result in 2 million years of healthy life lost due to disability. Now this is tiny compared to 100 million or so years attributed to alcohol or tobacco, but still results in a lot of pain and suffering. But what about our gum disease study? I thought the only physical health problems were dental in nature. Well, they were just looking at a specific set of health problems. They emphasized that the periodontal problems are in addition to all the other potential issues, like increased risk of accidents and injuries, bronchitis, heart attacks and strokes, possibly infectious diseases and cancer, as well as the mental health concerns, but in terms of as a more direct cause of death. Marijuana may be suspected in maybe hundreds of deaths over an eight-year period, whereas a single pharmaceutical drug, Viagra, was involved in thousands.