The reason nicotine fits into a receptor meant for acetylcholine is because the two have very similar shapes, biochemically speaking, Addy explains. This neurotransmitter is used to activate muscles in our body. The reward system wasn’t meant for drugs-it evolved to interact with natural neurotransmitters already present in the body, like acetylcholine. “Nicotine, alcohol, heroin, or any drug of abuse works by hijacking the brain’s reward system,” says Yale researcher Nii Addy, PhD, who specializes in the neurobiology of addiction. The unique attributes that make nicotine cravings persist There, nicotine particles fit lock-and-key into a type of acetylcholine receptor located on neurons (nerve cells) throughout the brain. It reaches the brain in about 10 seconds. When a teen inhales vapor laced with nicotine, the drug is quickly absorbed through the blood vessels lining the lungs. Because the mechanism is so engrained in the brain, it is especially hard to resist. It developed as a positive reinforcement for behavior we need to survive, like eating. The reward system, called the mesolimbic dopamine system, is one of the more primitive parts of the brain.

A key reason for this is that “the adolescent brain is more sensitive to rewards,” she explains. “Adolescents don’t think they will get addicted to nicotine, but when they do want to stop, they find it’s very difficult,” says Yale neuroscientist Marina Picciotto, PhD, who has studied the basic science behind nicotine addiction for decades. Nicotine can spell trouble at any life stage, but it is particularly dangerous before the brain is fully developed, which happens around age 25.

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