Huperzine A in Alzheimer's Disease

The selection process is designed to allow enrollment of all people with AD who are likely to be testable at the conclusion of the study period, and who do not have concurrent medical conditions or medications that might influence cognitive testing or that would increase the risk of treatment. Women and members of minority groups are encouraged to volunteer. Inclusion Criteria: * NINDS/ADRDA criteria for probable AD. * Mini Mental State Examination between 10 and 24, inclusive. * Stable medical condition for 3 months prior to screening. * Supervision available for administration of study medications. * Study partner to accompany participant to all scheduled visits. * Fluent in English or Spanish. * Age 55 years or older. * Modified Hachinski score equal to or less than 4. * CT or MRI since onset of memory impairment demonstrating absence of clinically significant focal lesion. * Able to complete baseline assessments. * 6 years of education, or work history sufficient to exclude mental retardation. * Able to ingest oral medication. * Stable doses of medications for 4 weeks prior to screening. * Physically acceptable for this study as confirmed by medical history, physical exam, neurological exam and clinical tests. Exclusion Criteria: * History of active peptic ulcer disease within 1 year of screening. * Clinically significant cardiac arrhythmia. * Resting pulse less than 50. * Active neoplastic (cancer) disease (skin tumors other than melanoma are not excluded; participants with stable prostate cancer may be included at the discretion of the Project Director). * Use of another investigational agent within 2 months of screening. * History of clinically significant stroke. * Current evidence or history in the past 2 years of epilepsy, focal brain lesion, head injury with loss of consciousness and/or immediate confusion after the injury, or DSM-IV criteria for any major psychiatric disorder including psychosis, major depression, bipolar disorder, alcohol or substance abuse. * Blindness, deafness, language difficulties or any other disability which may prevent the participant from participating or cooperating in the protocol. * Residence in a skilled nursing facility; but patients in an assisted living facility are acceptable. Excluded Medications: * Use of cholinesterase inhibitors (galantamine, rivastigmine, donepezil, and tacrine) within 2 months of screening. * Regular use of narcotic analgesics (\>2 doses per week) within 4 weeks of screening. * Use of medications with significant central nervous system anticholinergic activity within 2 months of screening (e.g. tricyclic antidepressants, diphenhydramine). * Use of anti-Parkinsonian medications (including Sinemet, amantadine, bromocriptine, pergolide, selegiline) within 2 months of screening. * Participation in any other investigational drug study within 2 months of screening (individuals may not participate in any other drug study while participating in this protocol). * Use of estrogen is allowed if the dose has been stable for 3 months prior to screening. * Use of vitamin E is allowed if the dose has been stable for 3 months prior to screening. * Use of memantine is allowed if the dose has been stable for 3 months prior to screening.