The bigger story with rapamycin is that the mechanistic target of rapamycin (mTOR) plays an absolutely crucial role in major diseases of modern civilization. One of the ways to inhibit mTOR for free is to simply stop consuming nutrients for extended periods of time.
As added information: metformin, a common anti-diabetic drug, is a inhibitor of mTOR. It potential adverse effects are less severe than rapamycin but are still significant. Specifically, long term usage can cause renal damage. Its mechanism of action has yet to be fully elucidated.
miRNA are order of magnitude smaller.