Some sedatives, antidepressants and other drugs can affect memory. Medications known as anti-cholinergic drugs are most likely have such an effect. These drugs block the action of the brain chemical acetylcholine. Common antidepressant anti-cholinergic drugs are Asendin (amoxapine) and Elavil (amitriptyline).

In a 2006 study, 372 seniors who were taking anti-cholinergic drugs were given regular memory tests over the period of a year. A control group was also tested. After a year, the researchers found that 80 percent of the seniors who had been taking anti-cholinergic drugs long-term were considered to have mild cognitive impairment. In contrast, only 35 percent of elderly who were not taking these medications were diagnosed with the condition. After eight years, however, those medication users who were diagnosed with mild cognitive impairment were no more likely to develop Alzheimer's disease than those who were not receiving these drugs.

(Marie L Ancelin, Sylvaine Artero, Florence Portet, et al: Non-degenerative mild cognitive impairment in elderly people and use of anticholinergic drugs: longitudinal cohort study. British Medical Journal, doi:10.1136/bmj.38740.439664.DE; published online, February 1, 2006).