In one trial, older adults on daily paracetamol gained more muscle
Over 12 weeks of leg training, adults around 64 to 67 taking 4 g of acetaminophen a day added 12.5% muscle volume against 8.6% on placebo. Eleven took the drug.
What the study found
Older adults on the maximum dose gained more muscle, not less
Across 12 weeks of knee-extensor training, adults aged around 64 to 67 taking 4 g of acetaminophen a day added 12.5% muscle volume against 8.6% on placebo. The investigators had expected the opposite. Biopsies found no difference in anything they measured that might explain it.
The caveat · Eleven people, one muscle measured
Eleven people took acetaminophen in this trial, out of 36 across three arms, and one muscle group was measured. Healthy older adults on a supervised programme are not a general population and not athletes. The dose was 4 g a day, the labelled maximum, which carries liver considerations this trial was neither designed nor powered to detect. The drug did nothing to the untrained hamstrings, so whatever is happening depends on the training rather than on the drug alone.
What we don't know
Eleven people took acetaminophen in this trial, out of 36 across three arms, and one muscle group was measured. Healthy older adults on a supervised programme are not a general population and not athletes. The dose was 4 g a day, the labelled maximum, which carries liver considerations this trial was neither designed nor powered to detect. The drug did nothing to the untrained hamstrings, so whatever is happening depends on the training rather than on the drug alone.