Friday, April 07, 2006

Dopey kids

A number of commentators (for example Yobbo) have criticised the view that the sale of alco-pops such as Mudslides and Breezers should be banned. I agree bans are clumsy, and unlikely to be effective, but I am sympathetic to the notion that the use of several drugs (alcohol, nicotine and cannabis), while harmful to all age groups, are possibly particularly harmful to people of age less than about 25. If bans are inappropriate - then at least people in this age group should be made aware of the particular risks. Perhaps advertising of such products should be restricted.

Neuroscience recognises that the human brain does not reach adult structure until around age 25. Tissue growth occurs throughout the brain in early childhood followed by a remodelling during teenage years - including refinement or pruning of cortical synapses (nerve connections) that ensures good connections are strengthened while less useful ones disappear. Pruning is accompanied by myelination that speeds neural connections and improves brain operation.

Remodelling continues beyond traditional adolescence and is concentrated in the cortex parts of the brain that regulate emotions and behaviour. Recent work suggests that adolescents are vulnerable to disturbances in brain development caused by addictive drugs. A useful survey is by Dan Lubman & Murat Yucel in the April 2006 issue, Of Substance. Consider:

Alcohol. Is a neurotoxin. It kills brain cells so alcoholics have smaller brains than light consumers of alcohol. Adolescents in particular are vulnerable to the effects of alcohol on memory-related brain functions. Research shows that the sizes of an adolescent's hippocampus and frontal brain lobes are significantly reduced by alcohol consumption.

And animal studies suggest that adolescent rodents can 'party harder' than older consumers without feeling sedated (this accords with high levels of 'binge drinking' among young people) while at the same time being subject to greater risk of disturbed brain development.

Nicotine. Animal experiments suggest nicotine is neurotoxic during adolescence though not during adulthood. Moreover, adverse effects on adolescents occurred even with much lower levels of exposure than typically consumed by regular smokers.

Cannabis. There has been much debate (including discussion here) about the links between cannabis use and psychopathology. This is a contentious area but again research is suggesting that, if there are adverse effects, these are most likely to be experienced at younger ages. Early onset cannabis use suggests increased risk of depression and psychosis. The explanation here emphasises links between genetic predisposition and cannabis exposure.

This is unsettled science and more research is needed. But there is the risk of a specific link between adolescent substance use and later psychopathology. While you can argue that young people should make up their own minds we know that, in youth, discount rates are high so agents are prone to impulsiveness. Thus, they can be better-off in terms of their own lifetime utility if early destructive impulses are curtailed. Indeed, as they age, these discount rates become lower. If risks are judged severe enough there are important implications for public health policy.


conrad said...

Like I always point out, at least for marijuana, the real risk are all those associated with smoking -- psychopathology is tiny in comparison.

If THC was legal, people would take that instead of marijuana, and even if there was a small increase in usage amongst younger people, I would suspect that this would trade-off with all the long term effects of inhaling carcinogens (which are huge).

The same is true for nictonine. Should we really worry about very minor effects (not unlike those that all of us who grew up with leaded petrol would have experienced), when there are huge obvious other risks ?

hc said...

Conrad, Is there evidence on these relative costs. The claim regarding nicotine sounds right, given cancer and other costs, but on cannabis seems less clear.

conrad said...

I haven't ever seen a relative cost paper (most of the stuff I have seen is in medical/psychology areas)-- but it is easy to see that the parameters we would need to lose are unlikely.

Lets make a few assumptions

1) Marijuana smoking is as bad as cigarette smoking (in fact, there are few papers coming out showing it has additive risk with cigarettes). Therefore 50% of people lose on average a fair few years of their lives. Only a smaller percentage of these people have their working productivity affected, since I am assuming it is generally at the end of their lives. These are just guesses [of course there are negative symptoms (e.g., higher rates of sickness that come much earlier vs. not claiming pensions, which I will ignore]. Lets give each user 4 years of lost productivity.

2) 20% of the population regularily smokes. So we lose 4 Million * 4 years = 16 million years at present.

3)If we legalize THC, we can reduce the overall negative symptoms of marijuana 50%. Everone now loses 2 years of their productive lives.

4)If we legalize THC, regular users go up 20%. We now have 4.8 million users losing 2 years of their lives. = 9.6 million years lost. (I find this unlikely incidentally -- I think the rates are already close to ceiling given the Australian rates are higher than those of the Netherlands)

5) If we legalize THC, not only more people smoke, but more people smoke more (probably still unlikely). Lets say we have +25% negative effects. Each user now loses 2.5 years of productivity. We now lose 4.8 times 2.5 years, i.e., 12 million years, which is much less than now.

6) Where is the breakpoint ? 16 million divided by 2.5. 6.5 Million users, including the 25% extra damage. So (using rather conservative assumptions), to lose out from legalizing THC, just in terms of productivity lost in people, we need 1.63 times as many people using THC instead of marijuana as now. Since I don't think there is really a supply problem with marijuana, I find this unlikely.

hc said...

Conrad, It's a thought-provoking numerical exercise. I'll think about it. The numerical assumptions seem reasonable. I'd be concerned that costs include psychosis and other non-physical costs that might be more likely with use of THC concentrate but I agree many of the physical costs would be reduced.

I agree with your general point that it is important to consider the costs of smoking as well as psychopathology.

I'd be interested in a reference which sumnmarised the direct health costs of nicotine and/or THC. I have read for example that nicotine can cause cardiovascular problems. These too would temper your conclusion.

conrad said...

I don't know enough about economics to evaluate the articles with regards to the direct economic costs of THC, but if I look at medline,

a lot of them (and they are not well cited -- showing the lack of research in the area) are coming from what looks to be completely politically motivated sources, so I presume there is huge bias, as is going to be the case with nictotine, which must be up there with all the other controversial issues in terms of mis-information. I am therefore not sure if any are considered non-biased definititive references, or whether a meta-analysis of them would be better (or for that matter, what would be the best way of evaluating them).

Another problem is that there is in fact very little research done into THC use by itself (its hard to get in most places, and most users are going to be multi-drug users). Even the medical-only properties have not been well investigated in people. Mainly mice have been used (and mice are of course tough little critters compared to humans)

Alternatively, I don't see any reason why the same amount of THC obtained in a clean form is going to be any more harmful than a smoked form, so in the worst case your estimation needs to only include the increased costs of increased usage upon legalization.

Smoke said...

Drugs are just bad, you should try to use Herbal Alternatives as a temporary replacement to loose the dependance!

Guitar Master said...

I wish I could blog as good as you, but what I can do is give you a nice Guitar Lesson!

Anonymous said...

This blog is so stupid. It assumes that people should live as long as possible. I want to live and die a pot head as soon possible and I am not alone.