Does paracetamol help with muscle pain?
Paracetamol probably does not relieve exercise-induced muscle pain any better than a placebo, and there are indications that it suppresses recovery substances in your muscles. Do not use it routinely after a workout, and if in doubt consult your doctor or physiotherapist.
Paracetamol probably does not relieve exercise-induced muscle pain (also known as delayed-onset muscle soreness) in any meaningful way. In a well-designed study with 60 healthy volunteers, 1000 mg of paracetamol taken over eleven days had no measurable effect whatsoever on pain, range of motion, or pain threshold following intensive exercise. That is striking, because it is precisely the situation for which many people reach for the drug.
The picture is equally thin when it comes to sports performance. In a randomised study with trained athletes, 1500 mg of paracetamol did not improve any performance measure, from bench press to jump height. Only caffeine produced a performance benefit. A small study (fifteen female athletes) did observe an improvement in running performance and lower perceived pain, but with so few participants that finding has not yet been confirmed.
At the same time, there are indications that paracetamol does something you may well prefer it did not. At the maximum over-the-counter daily dose (4000 mg), it suppressed the rise of substances in muscle tissue that normally increase after exercise and play a role in muscle recovery and muscle building. In the placebo group, one of those substances rose by 77% after training; in paracetamol users it actually fell by 14%. Whether this impairs muscle building over the longer term is less clear: studies lasting one and a half to four months observed no adverse effect on muscle mass or strength in people, and in older adults a slight improvement was even measured.
The practical conclusion: if you use paracetamol to get rid of muscle pain more quickly after a workout, the evidence that it works is very thin. Regular use around training sessions is additionally discouraged because of potential effects on recovery and muscle building, as well as the well-known risks to the liver and kidneys at higher doses. If you have persistent muscle pain or are unsure about painkillers in relation to sport, discuss this with your doctor or physiotherapist.
This answer is based on multiple randomised studies in humans, including two well-designed double-blind trials. The studies point predominantly in the same direction (no pain-relieving effect for exercise-induced muscle pain), but one small study of fifteen female athletes did find an effect. That makes the picture inconclusive. The studies on long-term muscle building are limited in size and duration. The evidence on biological mechanisms (inhibition of recovery substances in muscle tissue) comes partly from animal research, which makes the translation to humans uncertain.