What is the primary addictive substance found in tobacco?

The story behind the answer

Nicotine is the primary addictive substance in tobacco. Inhaled smoke delivers nicotine to the brain within seconds, where it binds nicotinic acetylcholine receptors and triggers a surge of dopamine in the brain’s reward pathway. This rapid, repeated reinforcement builds tolerance and dependence, and withdrawal can cause irritability, cravings, and trouble concentrating.

Nicotine is a plant alkaloid made by tobacco (Nicotiana tabacum) as a natural insecticide. A handy memory hook: NICOtiana → NICOtine → nicotinic receptors. By contrast, the other options come from different plants and