Open Label Study of Isotretinoin in Mild to Moderate Alzheimer's Disease

Inclusion Criteria: * Probable AD by DSM IV and NINCDS-ADRDA criteria * Females must be surgically sterile (bilateral tubal ligation, both ovaries removed or hysterectomy) or post-menopausal for at least 2 years. * \> 50 years of age * Residing in the community at baseline (includes assisted living facilities, long-term care nursing facilities) * Mini Mental State Examination at screen of 12-26 (inclusive) * No medical contraindications to study participation * Fluent in English at least 8 years of education. * Supervision available for study medication. Caregiver/study partner to accompany participant to all visits. Study partner must have direct contact with the participant \> 2 days/week * Able to ingest oral medication. * Neuroimaging (CT or MRI or PET) consistent with the diagnosis of AD at some time after the onset of the memory decline. * Clinical laboratory values must be within normal limits or, if abnormal, must be judged to be clinically insignificant by the investigator * Stable use of cholinesterase inhibitors and memantine is permitted if doses are stable for 3 months prior to enrollment. Dose should be stable throughout the study unless it is clinically necessary to adjust the medication. * Stable use of anti-depressants is permitted if doses are stable for 3 months prior to enrollment. Dose should be stable throughout the study unless it is clinically necessary to adjust the medication. Exclusion Criteria: * Dementia not due to probable Alzheimer's disease …