Nicotine

General 2: The blood-brain barrier

The oxygen-rich blood containing nicotine flows into the brain, where the blood vessels branch out into smaller and smaller capillaries.

The nicotine molecules are small enough to easily penetrate the blood vessel walls forming the blood-brain barrier, even though these are better protected against foreign substances than other blood vessels in the body.

The nicotine molecules move freely between the brain cells, where they produce their psychoactive effects.