An Interesting Opinion on Metformin
The evidence for metformin to slightly slow the aging process is all over the map. It is sketchy and contradictory in comparison to the robust results from rapamycin, for example. This isn't preventing a coalition of researchers from pushing forward on a clinical trial with the FDA, but I suspect that trial is much more a means of changing the FDA position on treatments for aging, which are currently not permitted, than an attempt to show results from metformin. Metformin is useful there because it is an established drug with a much lower set of regulatory barriers for reuse in other contexts, making it harder for regulators to throw roadblocks in the way of a trial to treat aging.
A researcher offers an interesting opinion on metformin in this open access paper. In his view the evidence for modestly reduced cancer rates resulting from metformin use is already good enough that, given the very low cost of the drug, it should be formally adopted and verified for cancer prevention in the general population. This is perhaps best considered in the context of the debate of two years ago over whether rapamycin extends life by reducing cancer risk or slowing aging:
During the last decade, there has been a burst of interest in the antidiabetic biguanide metformin as a candidate drug for cancer chemoprevention. Analysis of the available data has shown that the efficacy of cancer preventive effect of metformin (MF) and another biguanides, buformin (BF) and phenformin (PF), has been studied in relation to total tumor incidence and to 17 target organs, in 21 various strains of mice, 4 strains of rats and 1 strain of hamsters in a wide range of doses and treatment regimens. In the majority of cases (86%) the treatment with biguanides leads to inhibition of carcinogenesis. In 14% of the cases inhibitory effect of the drugs was not observed. It is very important to note that there was no any case of stimulation of carcinogenesis by antidiabetic biguanides.The history of biguanides in oncology started in the 1970s, is rather dramatic, and seems not to come to "a happy end" at the present time. The first publications in 1974-1982 showing the high potential of PF and BF in prevention of spontaneous and induced carcinogenesis were not met an interest adequate to the degree of real importance of these finding. Whereas both in vitro and in vivo experiments provide new evidence of anti-carcinogenic potential of biguanides, and the majority of clinical observations clearly demonstrates protective effect of MF in relation to many localization of cancer, there are some publications on results of clinical trials that are inconclusive and sometime were demonstrated adverse effect of MF. Recently a researcher explaining possible reasons for this inconsistency cited the rather sardonic comment of a leading scientist in the field: "The problem with metformin is it's cheap, it's widely available, it has a great safety profile, and anyone can use it". Really, it is difficult to say better... In PubMed, under the words such as "metformin and cancer" the number of indexed papers were increasing exponentially from zero in 1990 to more than 2500 last September. Among them around 185 reviews on the topic were published just in the last 5 years. There are too many works and still no final conclusion. It may be the time to make this long story short; we believe that efficacy of MF should be evaluated according to criteria, experience and rules of the WHO International Agency for Research on Cancer.