His sust may be under-dosed, poor diet, or could be life-factors. Lots of people can't gain a lb of muscle without enough sleep, or too much stress.
Since it's not working, he should definately try switching up everything. Try a different training ruitine, change the diet up abit, ensure he's getting enough sleep, do eod injects.
Even small simple changes can make a huge difference.
Example = instead of eating chicken for a meal, he could eat beef or fish.