I recently listened to a podcast from Fresh Air in which the host Terry Gross interviewed Judith Griesel on her book "Never Enough: The Neuroscience and Experience of Addiction."  In it, she talks about the neuroscience behind addiction and how certain drugs react with brains in general, but with adolescent brains in particular.  Here is some of the transcript:

GROSS: You started drinking when you were 13, which is pretty young. Why is it especially bad to start drinking and using drugs when you're still an adolescent?

GRISEL: Yes. It really - we're seeing more and more how this period in adolescence, when people are figuring out who they are, what they care about, what they like, what they dislike, who they want to be with, what they want to study, all those things are that way at this time because their brain is so plastic. And what I mean by plastic is it's undergoing unbelievable amounts of remodelling.

So, the changes in behaviour that happen during adolescence are so important and lasting because the brain is forming permanent structures. So, whatever you experience as an adolescent is going to have a much more impactful influence on the rest of your life trajectory than it would, say, if you did this at another time in development when your brain wasn't so prone to change.

GROSS: So, since your brain is very plastic and still modelling when you're an adolescent if you start using alcohol or any drug when you're, say, 13, like you did, does it change the way your brain matures?

GRISEL: Yeah. So, when the circuits are being laid down, if they're laid down under the influence of a drug then they're going to be laid down differently than if it's not under the influence of a drug. If you start using at 28 when the circuits are already more or less set then you're not going to have such a long-lasting impact.

GROSS: Are you more likely to become addicted if you start using alcohol or any kind of addictive substance and you're an adolescent?

GRISEL: Absolutely, for exactly this reason. So, 80 percent, at least, of people who have a substance use disorder started before they were 18.

They then went on to discuss how alcohol and cocaine affect the brain.  I want to include the transcript for their discussion of how marijuana effects teen brains:

GROSS: So, explain that a little bit more in terms of the effects of marijuana.

GRISEL: So, when we smoke marijuana, the whole brain is flooded with THC, and that causes the cell-to-cell - to communication in cells throughout the brain to be enhanced or to be exaggerated. And that's really fun because it seems like, wow, everything is so interesting. Everything is beautiful. The music is so rich. The colours are so wonderful. The food is delicious. Everything at once is turned on. That's not how the natural system would work. It would work sort of with discretion. But anyway - so all over the brain, it's enhanced. And that makes everything seem richer and more interesting.

What's unfortunate is the brain does adapt to that, and it adapts by decreasing the number of sites that THC can have an effect. So those sites downregulate, meaning they go away over time. And it doesn't take long, but regular use - the more you use and the more often you use, the less of those receptors there will be or those sites for THC to act there will be. And that means that when you have THC, things aren't quite that great. They used to be wonderful, and now they're just pretty good. But when you take away the drug, then things seem sort of lifeless and grey and maybe less interesting.

GROSS: Oh, are you describing a form of addiction?

GRISEL: I think so. So, there is an addiction to THC, and we know that it stimulates dopamine in the - in that pleasure or news pathway. And that's really the definition of whether or not a drug is addictive. It does so more in some people than in others, but of course, those are the ones that are at risk for addiction. It also causes tolerance, like I'm describing.

So, if you smoke regularly, then there are fewer sites for the THC to act. And therefore, you need more to try to produce the same effect, which eventually, you won't be able to do. So, you're dependent, also, because when you take the drug away, things are not as good as normal.

You can listen to the entire podcast at https://www.npr.org/programs/fresh-air/. At Gobi, we are very concerned about teen use of marijuana.  An unofficial reality check is that about 90% of the parents that contact us do so because of their teen smoking weed.  Marijuana is addictive, not for everyone but teens are almost twice as likely to become addicted as adults.