Thirty years of teaching college students about the effects of drugs upon their brains and I am still astonished at the continued attraction of illicit drugs. Year after year, the story never really changes. Their reasons for taking psychoactive drugs are varied but their rationalization has remained fairly consistent: they simply do not believe that anything truly bad will ever happen to them. They are young, their lives stretch out before them to the horizon and they feel immortal. I speculate that the consistency of this reasoning across decades is likely due to a developmental feature of the human brain.
I blame the feelings of immortality of teenagers on the fact that their frontal lobes are not fully working. The reason the frontal lobes are not fully engaged is because they have not yet completed the process of neuronal myelination. Think of myelination as the insulation on the electrical wires inside your house. Without myelination in the brain, electrical signals from neurons fail to reach their destination. The parts of our brains that myelinate last are also the parts that evolved most recently. These parts include our frontal lobes, which contribute most to our unique personalities and allow us to anticipate the consequences of our actions. Essentially, your frontal lobes tell you that it's a bad idea to drink alcohol and drive or to ignore the consequences of taking heroin. When your frontal lobes finally complete their process of myelination, they begin to work properly and you stop doing dangerous things. Most importantly, you stop feeling immortal. Apparently, women finish this myelination process by age 25 years and men finish by age 30. Thus a 20-year-old female, although her brain is still myelinating, is closer to maturity than her 20-year-old boyfriend, who still has another 10 years before he can really appreciate the wisdom of warnings such as those against drinking and driving or against taking any drug that comes his way.