How creatine, leucine or HMB may enhance the effect of anabolic steroids
If athletes do decide to use anabolic steroids, they might consider combining their gear with supplements such as creatine, leucine or HMB. These supplements could enhance the muscle enhancing effect of anabolic steroids. We deduce this from an animal study that Australian pharmacologists published in Andrologia in 2016.Study
The researchers compared the biological effects of testosterone enanthate with those of trenbolone enanthate. They injected these two anabolic steroids into neutered rats for four weeks, and afterwards determined the anabolic effect of these agents by studying the rats' levator ani muscle.

The researchers gave the rats in the testosterone group seven times the dose they gave the rats in the trenbolone group. Trenbolone is a more aggressive anabolic than testosterone.
In terms of anabolic effect, trenbolone and testosterone - at least in the doses used - were well matched. The two steroids increased muscle mass and muscle size in equal measure.

The Australians also found that both testosterone and trenbolone increased myostatin production.
Myostatin inhibits muscle growth. It is a hormone released by muscle cells and interacts with receptors that are also in muscle cells.

Wild speculation

Testosterone and trenbolone also increased the production of proteins that neutralize myostatin. This explains why the net effect of the administration of the two steroids was still positive, but it does make you think.Suppressing myostatin while taking classic anabolic steroids could be surprisingly effective, we suspect. This could be done with supplements such as creatine, leucine and HMB.
If you give people creatine, the concentration of myostatin in their blood decreases. The effect is not great, but it is statistically significant. In vitro studies suggest that myostatin inhibition is increased by combining creatine with leucine and HMB.
Andrologia. 2017 Apr;49(3).