OBJECTIVES:   The aim of this study was to evaluate the efficacy for five FDA approved drugs for Alzheimer's disease.  METHODS:   MEDLINE and the International Pharmaceutical Abstracts databases were searched for studies addressing functional outcomes with Alzheimer's disease.  The primary outcome was cognitive efficacy and must have been measured on a validated scale.  To report one consistent scale value, values were transformed into z-scores to obtain a dichotomized output, categorized as either improvement or a lack therof in treatment.  Odds ratios were calculated for success for each drug treatment.  Winbugs version 1.4 statistical software was used to conduct a mixed treatment comparisons Bayesian analysis along with a sub-analysis to examine whether or not the cognitive measurement scale used in the studies effects the ranking of drug treatments. RESULTS:    The mixed treatment comparisons results showed that galantamine OR=2.518E+7, 95%CRI: 447,300-7.034E+9 was highly favored above all other Alzheimer’s treatments, followed by donepezil OR=1557, 95%CRI: 315.4-8341, tacrine OR=212.8, 95%CRI: 28.47-1604, rivastigmine OR=23.57, 95%CRI: 5.397-104.8, memantine OR=3.775, 95%CRI: 0.639-23.09 compared to placebo.  The sub-analysis also showed that galantamine OR=2.832E+7, 95%CRI: 483900-2.326E+10 as highly favored, but yielded slightly different results with tacrine OR=1434, 95%CRI: 148.2-15830 ahead of donepezil OR=471.2, 95%CRI: 83.48-2935 in ranking, followed by rivastigmine OR=19.54, 95%CRI: 4.781-83.19 and memantine OR=2.836, 95%CRI: 0.2196-37.96.  This analysis removed the eight studies that did not use the ADAS-Cog measurement scale, suggesting that the selection of the cognitive measurement scale changes the ranking of drug treatments.  Odds ratios for galantamine were high due to the favorable response (≥95) for the drug.  The severity of Alzheimer’s disease was not taken into account in this study. CONCLUSIONS:   The consistency between drugs in terms of cognitive efficacy is present in all five drugs; all demonstrating effectiveness over placebo.  Future research in this area is needed, including clinical studies comparing the agents directly.