Prodromal AD clinical trial methodology is advancing rapidly. It is now possible to more accurately identify MCI patients with underlying AD pathology at an earlier stage of the disease through the use of amyloid imaging and CSF biomarkers. Measurement of decline in these early stage clinical trials using continuous clinical and cognitive outcome measures is conceptually more appealing and adds greater efficiency compared to the classical outcome of "conversion" to dementia used in prior MCI clinical trials. Nevertheless, the fact that many prodromal AD patients who are likely to be recruited to these early stage studies are not taking acetylcholinesterase inhibitors at the time of enrollment, but are poised to start taking them over a multi-year period of follow-up, is a potential confound that needs to be addressed.