Some people believe the ‘gateway effect’ exists because early drug use primes the human brain for more drug-seeking, others argue that the friends you make using drugs as a youth are a ready source for other drugs later, and still others argue that there are factors, like impulsivity, that causes both early and later drug use. Which camp is correct? Probably, all of them.

That’s a comment by an eminent scientist on a new Yale University research study showing that use of cannabis, alcohol and tobacco in adolescence predicts abuse of prescription medications later in life (though the effects are more consistent for males than females).

From an ideological standpoint, it is necessary to have one and only one gateway hypothesis. Many drug legalization advocates attack the idea that any part of the relationship between early and later drug use could be causal. Rather, they insist that the relationship is 100% explained by social network effects (i.e., friends who give a young person access to alcohol and cannabis become a source of other drugs) or by an unknown third factor, such as impulsivity, that causes both early and drug use. Many ideologues on the prohibition side do the reverse, claiming that 100% of the relationship is causal and that invocation of social networks and third factors as explanatory factors is flummery.

But from a scientific viewpoint, there is nothing wrong at all with saying that part of the effect is causal (early drug use in part truly causes later use), part of it is a social network effect, and part of it is a third factors effect. Science is thankfully more accepting of complexity than ideology, which is particularly important when trying to solve a puzzle as intricate as human development. And in any case it’s rather ridiculous that discussions about drug gateway effects are held captive to legalization debates when the key gateway drugs (alcohol and tobacco) are already legal.

[Cross-posted at The Reality-based Community]

Keith Humphreys

Keith Humphreys is a professor of psychiatry at Stanford University. He served as a senior policy advisor at the White House Office of National Drug Control Policy from 2009 to 2010.