Dietary restriction increases lifespan and reduces in prevalance of most age-related diseases. Therefore a pill that mimics effects of dietary restriction would be expected to have similarly protective effects.
The news program "60 Minutes" recently reported on the prospects of an "anti-aging" pill based on resveratrol, a flavinoid found in red wine, which activates sirtuins, an HDAC which is reported to mediate the protective effects of dietary restriction. The company that has done the most to develop this idea is sirtuis, which is developing derivatives of resveratrol that are even more potent activators of sirtuins.
On the other side of the respectability scale are approaches advocated by Aubrey de Grey, who strongly argues that his proposed strategies are likely to greatly increase lifepsan of many of us currently alive. Although de Grey's strategy is considered ludicrous by many scientists, including yours truly, judging by the startling number of attacks on these critiques, de Grey appears to have a fairly large following.
Historically, gerontologists have been hesitant to discuss the prospects of a drug that could substantially increase lifespan, and healthspan, by targeting fundamental mechanisms driving senescence, since "anti-aging" preparations have long been tainted by obvious fraud, and in any case the whole idea seems faintly disreputable. However, I think it's time we come out of the closet on this.
For the record, I actually do think it may be possible to develop drugs that mimic effects of dietary restriction, as drugs being developed by sirtris are reported to do. I'm actually not convinced that sirtuins are the best target for such drugs, but we and others have plausible alternative targets. Would it be a good thing if there were such drugs? They would potentially reduce the incidence of all age-related pathologies known to be ameliorated by dietary restriction, including Alzheimer's disease and cancer. It's hard to argue against the development of drugs with such potential to reduce human suffering. Such drugs would also likely increase lifespan. It is this latter possiblity, "playing God" in some people's minds, that raises the most ambivalence. Very possibly social dislocation would occur. However, the contraceptive pill produced similar ambivalence, and now it is simply the part of modern life, and, to most people's minds, that's a very good thing.