There's two questions about haram nature of smoking cigarettes Why is smoking tobacco haraam? and Is smoking allowed in Islam?. However, none of the answers address whether or not nicotine is considered an intoxicant.
Nicotine's mood-altering effects are different by report: in particular it is both a stimulant and a relaxant. First causing a release of glucose from the liver and epinephrine (adrenaline) from the adrenal medulla, it causes stimulation. Users report feelings of relaxation, sharpness, calmness, and alertness.
It's not clear from this whether or not nicotine is an intoxicant.
A relevant hadith is The Prophet [SAW] forbade a small amount of whatever intoxicates in large amounts. Sunan an-Nasa'i 5609 (grade: hasan). And certainly, a "large" amount of nicotine causes nicotine poisoning (actually it's quite small: "0.5-1.0 mg/kg can be a lethal dosage for adult humans"). But I'm not sure if "poisoning" would be considered "intoxication".
Question: Is nicotine considered an intoxicant?