The primary goal of this study is to test the hypothesis that three months of administration of EST to 1) normal post-menopausal women, and 2) female patients with mild-moderate AD who are concurrently treated with anticholinesterase therapy (donepezil), will positively change or blunt the negative and behavioral effects of drugs that block central cholinergic receptors (both muscarinic and nicotinic). Participants will be blindly placed on EST or placebo for three months each. After each three month period, they will be cognitively assessed after receiving single doses of the cholinergic antagonists scopolamine and mecamylamine. These results will have direct implications for the use of EST in post-menopausal women as well as interactive treatment with cholinergic drugs for AD. Researchers plan to recruit a total of 45 women (30 healthy, and 15 patients with AD).