The research seems to go back and forth on this (just like coffee).
Now it seems like these drugs may not be so bad for muscle gain, especially in >35’s.
Effects of Prostaglandins and COX Inhibiting Drugs on Skeletal Muscle Adaptations to Exercise.
It has been ~40 years since the discovery that prostaglandins are produced by exercising skeletal muscle, and since the discovery that inhibition of prostaglandin synthesis is the mechanism of action of what are now known as cyclooxygenase (COX)-inhibiting drugs. Since that time, it has been established that prostaglandins are made during and after aerobic and resistance exercise and have a potent paracrine/autocrine effect on muscle metabolism. Consequently, it has also been determined that orally consumed doses of COX-inhibitors can profoundly influence muscle prostaglandin synthesis, muscle protein metabolism, and numerous other cellular processes that regulate muscle adaptations to exercise loading.
Although data from acute human exercise studies, as well as animal and cell culture data would predict regular consumption of a COX-inhibitor during exercise training would dampen the typical muscle adaptations, the chronic data do not support this conjecture. From the studies in young and older individuals lasting from 1.5-4 months, no interfering effects of COX-inhibitors on muscle adaptations to resistance exercise training have been noted. In fact, in older individuals a substantial enhancement of muscle mass and strength has been observed.
The collective findings of the prostaglandin/COX pathway regulation of skeletal muscle responses and adaptations to exercise are compelling. Considering the discoveries in other areas of COX regulation of health and disease there is certainly an interesting future of investigation in this