Doctors, what are the effects of nicotine withdrawal and how long does it take for the effects to happen?

Many effects and: a short time after last use. Nicotine is a short-acting drug, which is why people who smoke average 1-3 cigarettes per hour while awake (as opposed to heroin 3-4X/day). Withdrawal consists of anxiety, craving for tobacco, muscle tenseness, insomnia and irritability. It occurs within 4-7 hours after last dose, which is why very dependent smokers need a cigarette as soon as they wake up.