Is rapamycin hard on the liver?
Based on the available studies it cannot be established whether rapamycin is hard on the liver; the supplied sources actually use it as a protective agent in animal models. Anyone considering rapamycin is best advised to have their liver function checked regularly by a doctor.
The available studies do not examine rapamycin as a possible cause of liver damage. None of the sources identified liver toxicity as an outcome in humans or animals using rapamycin as a drug or supplement.
What the studies do show is almost the opposite. In one mouse study1, rapamycin was administered before mice received a harmful dose of paracetamol. The compound activated autophagy, a kind of cellular self-cleaning system, and this reduced the liver damage that normally results from such an overdose. Rapamycin played a protective role here, not a harmful one.
A second study2 confirms this picture in a different harmful context: exposure to zinc nanoparticles. Here too, researchers used rapamycin to activate autophagy, after which liver cells were better protected against a harmful form of cell death. Both findings come from animal and cell studies, not from research in humans, so they say nothing about what rapamycin does in healthy people who take it over the long term.
The question of whether rapamycin places a burden on the liver in humans, at the low doses used in anti-ageing contexts, cannot be answered on the basis of these sources. Appropriate research on this topic is simply absent from the supplied material. Anyone considering rapamycin would be wise to do so under medical supervision, with liver function values also being monitored.