I forget who wrote it but I found this a few years ago In case you were wondering about the difference between caffeine & nicotine: "Caffeine and nicotine are different in their actions as stimulants. Caffeine is a non selective methyl xanthine phosphodiesterase inhibitor that serves to increase intracellular cAMP (a second messenger). When cAMP is elevated, cells become more excitable. There are two primary second messenger molecules, cAMP and cGMP. cAMP is more prevalent in neurons that lead to behavioral (and brain) excitation (dopamine, norepinepherine, epinephrine, etc), although it is also found in monoamine neurons that are associated with behavioral depression and sleep (e.g., serotonin). So, the stimulant action one sees from caffeine is largely due to hyper-excitation in the excitatory neurons neurons. The reason caffeine causes sleeplessness is because it is acting on the same systems affected by amphetamine and ......., except with a much lesser overall effect. Nicotine is a nicotinic acetylcholine agonist. That is, it acts directly on acetylcholine nicotinic receptors where it mimics the effects of acetylcholine. The preponderance of nicotinic receptors are contained in the peripheral nervous system. It is nicotinic stimulation that causes contraction of striate muscles that allow for body movement. The nicotinic receptors on the blood vessels cause constriction. In the brain, nicotinic cholinergic receptors are involved in learning and memory, concentration, and many other processes. The stimulant effects one sees from nicotine is largely due to its net effect on brain systems. It is not a behavioral stimulant the way caffeine is. In fact, nicotine has both activating and sedating properties, but the activation is much less behavioral in nature. The reason that it doesn't interfere with sleep is because of that. I didn't intend to make this a pharmacology lesson."