Nicotine is a cholinergic agonist that also has a presynaptic effect in releasing acetylcholine. It has been shown to reverse spatial memory deficits produced in rats by lesions in the medial septal nucleus of their brains, and, in aged monkeys, nicotine administration improves memory and alertness to visual stimuli. Observational studies have suggested a protective effect of smoking against Alzheimer's disease, but recent studies have called this into question. Smoking is a risk factor for stroke and so, possibly, for vascular dementia. Because nicotine has adverse effects, it is important to conduct a systematic review to assess its clinical efficacy and safety for people with Alzheimer's disease.