Why Politicians' Lazy Takes on Weed's Link to Mental Illness Need to Stop

Legal weed recently celebrated its first birthday and the movement, which has been toddling forward, seems almost ready to run. But as 420 friendliness is written into our laws, the dialogue on pot’s health risks and benefits has continued among scientists. Every so often, studies linking psychosis with marijuana use receive coverage, but they aren’t at the core of the American drug conversation, which remains stuck in a “better or worse than cigarettes/alcohol” place. In countries with established pot cultures, notably the UK, this research is treated as cause for — if not alarm — consideration. Americans on both sides of the debate about legalization seem unprepared to have the mental health conversation.

There’s a decade’s worth of studies examining the relationship between weed and schizophrenia. You’d think American politicians against legalization, like Republican presidential candidates Chris Christie and Marco Rubio, would mention the research in their litany of marijuana’s ills, but instead they list the usual fears about weed’s role as a gateway drug and in decreased productivity. The National Institute on Drug Abuse reports that long-term marijuana use has been linked to worsening symptoms in patients with schizophrenia but otherwise says little else. Ditto the National Institute for Mental Health, which reports “increasing evidence” of a link.

Meanwhile, in the UK, warnings from national institutions take a tougher stand. The National Health Service often reports on studies linking psychosis with marijuana and claims that regular use is associated with an increased risk of developing psychotic illnesses and increasing the risk of relapses in people with existing schizophrenia. Likewise, the Royal College of Psychiatrists claims that science provides “sufficient evidence” to show that teenagers that smoke pot have a higher than average risk of developing schizophrenia or bipolar disorder — most likely because it interferes with adolescent brain development.

Even international agencies like the UN Office on Drugs and Crime err on the side of caution. In its 2012 review of worldwide pot use, it reported:

“The most consistent linkages are between cannabis use and psychosis, and there are sufficient data to suggest that cannabis use can play a causal role in the emergence of psychosis in some patients depending on their genetic makeup, age of first use, and other factors.”

It’d be inaccurate to say that any of these agencies get the science wrong, but what parts or how much of the existing research each chooses to publicize clearly varies. There’s a lot of data to parse. The sheer number and variety of the studies suggests that the nature of the pot-schizophrenia link is far from straightforward.

One leading theory is that certain individuals are genetically predisposed to weed-triggered psychosis, but few studies have shown evidence of this. Other studies have suggested that pot smoking is a catalyst for the onset of psychotic illnesses. Still other research points to weed as the cause.

The most recent large-scale study investigating the link between cannabis use and the development of schizophrenia, however, dismissed many of the existing studies, saying they failed to provide “conclusive evidence” that cannabis use may cause psychosis. The study, published in Schizophrenia Research early last year by a team from Harvard Medical School, concluded that pot use could be risky for people predisposed to schizophrenia but was not itself the risk:

“The results of the current study suggest that having an increased familial morbid risk for schizophrenia may by the underlying basis for schizophrenia in cannabis users and not cannabis use by itself.”

In an ideal world, the interpretation of scientific data wouldn’t be dictated by geography or culture. But the reality is that health policymakers in the U.S. and abroad have access to the same pool of studies and still manage to pull out very different take-home messages, suggesting that other biases are coming into play. In this case, differences in American and European drug culture need to be taken into account.

Surprising as it may sound to frustrated pot activists stateside, American attitudes toward marijuana among both users and legislators are relatively more relaxed and positive than they are across the pond. Pot smoking among American college kids has hit a 35-year high, and legalization is only gaining traction. Meanwhile, weed is still illegal throughout the U.K., and marijuana use among Brits aged 15-34 has fallen by almost 50 percent over the last 15 years. In light of these trends, the fact that UK policymakers are more willing than their American counterparts to err on the side of caution really isn’t that surprising.

Ultimately, different nations have different needs. Variations in interpretation shouldn’t be taken as evidence of any agency’s failure to properly acknowledge the science at hand. Instead, they’re a call to keep the conversation going — and for scientists to collect more conclusive data.