Studies on Alzheimer Disease - Metformin Connection - A Brief Review

Metformin is the widely prescribed first line oral antidiabetic drug used in diabetes mellatus, type 2 . The global sales turnover of metformin runs into millions of dollars. The Increased risk of  metformin (Met) users for developing  Alzheimer disease (AD)is reported first in a study conducted in 2011.  Since then, the subject has attracted the attention   of the researchers as well as the pharmaceutical industry, resulting in a number of studies, both clinical as well as experiments on animals. Confusing results poured in , ranging from confirmation of the risk of AD to protection  against developing AD , making the scenario, all the more intriguing . Added to the confusion, is the diversity of various studies as well as the parameters interpreting their results. Of the many clinical trials, some are retrospective cohort studies (Tseng Chin-Hsiao 2019) , case control  studies (Imfeld P, et al.) Randomised studies (Hsu CC, et al.),  double blind , cross over pilot studies. (Aaron Koenig et al.)  and some longitudinal studies (Ng TP, et al.) , besides studies doing  meta analysis . Of these studies most of the trials estimate the risk of development of dementia with metformin alone (Tseng Chin-Hsiao 2019) or in comparison with other OHAs (Hsu et al, Cheng et al.) .The other studies studied the effect of metformin on the cognition. (Moore EM, et al.). These trials have different out come measures, (like Hazard ratio, (HR) Odds(OR) ratio, relative risk (RR) etc.) which don’t mean one and the same. So the multiplicity of the types of studies and different out- comes with different conclusions will be surely baffling to an average reader who tries to take cognisance of the involved issues. The article attempts to take stock of the overall developments in this regard. The author adopted a reader friendly approach which is discussed in the article, at the outset. Finally, it is  reiterated that future prospective studies only can resolve the conflict of opinion on the nexus between metformin and Alzheimer’s disease.