The Drug Update

This study addresses "whether Delta-9-tetrahydrocannabinol (THC) exposure during adolescence modulates opiate reinforcement". But the gateway is about the likelihood of a cannabis consumer progressing to heroin. In order to do that, the user first has to try heroin. In this experiment, all the rats were hooked up to a heroin source. What we can derive from this study is that if a person with adolescent cannabis use history tries heroin, they are more likely to get addicted compared to someone who tries heroin without a history of adolescent cannabis use.

But the key question is what proportion of cannabis users try heroin in the first place and why? Neurobiology won't help you there.

This sounds an awful lot like the study where monkeys were addicted to cocaine, and then forced to undergo withdrawal while being hooked up to a THC dispenser.

The outcome was predictable: the monkeys sought to reduce the edge caused by cocaine withdrawal by self-adminstering THC. This was twisted by the prohibs as being 'proof' that monkeys have a capacity for self-administering THC, and therefore THC was 'addictive'. The role of the cocaine was very quickly glossed over, like those breathy, strung-together side-effects warnings from pharmas advertised on the Tube. Prohibs have no shame; they'll tell any lie they believe will be believed, and know most people don't have the necessary impetus to check them on their 'facts'.

Daksya: Obviously the study doesn't address how THC affects opiate initiation. However, the substance is still relevant. Thinking in terms of harm minimization, understanding what leads to increases in addiction probablity rather than initiation may be more important.

Kaptinemo: The "gateway theory," while commonly used by prohibitionists to justify marijuana's legal status, doesn't necessarily prescribe prohibition as a strategy. The study concluded that marijuana use leads to increased opiate sensitivity and higher maintainence levels, not that marijuana should be prohibited. The study shouldn't be knocked for what some people will inevitable draw from it.

Matt, the study says, "Several epidemiological studies report that early regular use of cannabis increases the risk of initiation of the use of other illicit drugs (Agrawal et al, 2004; Fergusson and Horwood, 2000; Lynskey et al, 2003; Yamaguchi and Kandel, 1984), supporting the cannabis gateway hypothesis of cannabis as a steppingstone toward abuse of other drugs."

This study doesn't address the gateway effect at all. It just addresses differential effects on those who have already crossed the gateway. The main point of prohibiting cannabis on the gateway basis is to stop initiation.

Just to reiterate my point.

Here's an article about this finding in ScienceNOW:

"Whether this indicates marijuana is a "gateway" drug depends on the definition of "gateway," says Hurd. She says both groups of animals took the same amount of time to start taking heroin, suggesting THC use doesn't start them on the path to hedonism, but the THC-primed rats got more into it, suggesting it paves the way for increased use."
(Hurd's the lead author of the paper)

and

"But pharmacologist Aron Lichtman at Virginia Commonwealth University in Richmond inserts a note of caution. "The data really are very provocative," he says, but not conclusive. He questions whether other reward-reinforcing behavior, such as eating food, would also be increased under these conditions."

The main point of prohibiting cannabis on the gateway basis is to stop initiation.

We agree. I agree with you that this doesn't provide evidence for prohibition. However, if the gateway theory assumes that marijuana use leads to increased drug use later, then this provides evidence for that. However, if the theory limits its scope to assuming only an increase in initiation rates, then my title is unfitting.

The IOM's 1999 study found that:

There is no conclusive evidence that the drug effects of marijuana are causally linked to the subsequent abuse of other illicit drugs.

Here they use "abuse" rather than initiation, so I feel justified in using gateway theory in the title. Again, though, I do not make the critical assumption that the gateway theory prescribes prohibition of marijuana.

Matt, the lead author is ambivalent (in the above quote) about the conclusion of the study with respect to gateway theory. The study is clear: those who use heroin after pot, use more of it. The notion of gateway is that "if my kid does pot, he's more likely to do heroin", NOT "if my kid does pot, and then heroin, he's more likely to do more of heroin". Adopting the second version assumes that people are more worried about regular use of heroin, but okay with experimental use. For a drug that has the reputation of "so good, don't even try it once!", that seems unlikely.

Here they use "abuse" rather than initiation

If you read the DEA scheduling guidelines (3rd bulleted point), abuse can mean just any self-initiated use of a drug, not necessarily 'problematic' use. So, I wouldn't read too much into the word 'abuse'.