Many of those are like dopamine, chemicals that cause a feel-good sensation. That leaves people wanting more, he said. The blood-brain barrier, a thin membrane surrounding, is effective at keeping out most foreign bodies. And the human immune system is programmed to attack large pathogens in the blood, like bacteria or viruses. Nicotine, however, evades the immune system and has no problem slipping into the brain because its molecules are tiny.
Scientists often battle disease or infection with drugs that block the receptors an invader seeks.
But that is not a particularly good approach in the brain. If you block them, you might get side effects that you don't want. Best, of course, would be to stop nicotine from reaching the brain at all. That means activating the immune system while the tiny nicotine molecules are still only in the blood. Researchers already knew how to force tiny molecules to bind to larger ones to create a big foreign substance the immune system could not miss.