Nicotine

Nicotine is a strong neurotoxin - it affects the nervous system.

An excerpt from the article 15 facts about nicotine

It affects the nervous system, causing pleasant experiences that can be compared to the effects of taking hard drugs: cocaine, amphetamine, or morphine. The dose taken is important, although, regardless of the size, it always leads to addiction. When lethal doses are used (LD50 is approximately 1-1.5 mg/kg body weight), death may occur within a few minutes as a result of suffocation, because neurotoxins cause acute paralysis of the respiratory muscles.