Most of the people who have participated in rapamycin clinical trials have been very sick, organ transplant patients who are typically taking many different drugs. As a result, we don’t have much data on the risks in healthy people taking rapamycin.
Additionally, what data we do have in terms of potential health risks of rapamycin comes from continuous dose rapamycin in mice, and very high continuous doses used in transplant patients. Neither of these situations translate well to lower dose, pulse-dosing of rapamycin that is typical in anti-aging applications.
Two adverse outcome risks that have been seen sometimes in mice (cataracts) and transplant patients (lower testosterone and spermatogenesis) have been identified by Prof. Matt Kaeberlein as being potentially concerning.
The increased risk of cataracts is seen in some mice studies that are daily dosed at higher levels of rapamycin. Trends of decreases in testosterone and spermatogenesis has been seen in mice and transplant patients who have used rapamycin daily, but the effects seem to be similar to that seen in caloric restriction (perhaps an evolutionarily conserved response to low food availability; when food supplies are low, mammals need to focus on survival and not procreation). As with caloric restriction, when daily high doses of rapamycin are stopped, testosterone and spermatogenesis seems to return to normal.
These types of potential risks are why most people taking rapamycin for anti-aging take it in pulsed dosing (once weekly doses) and also take longer periodic breaks from even the weekly schedule (e.g. taking one month off every 3 or 4 months).
Read the Full Story: Possible Rapamycin Risks (part 2)