In reference to melatonin -
Ok, well let's start with the fact that NONE of us parents here are veterinarians nor scientific researchers so we have to rely on those who are and the proven results of their combined expertise. Not that we can't, or shouldn't, question them - but we simply do not have their knowledge nor experience so it is wise to listen.
Now let's look at that term "suggested" - this means there is a possibility only, not that anything has been
proven - proof that can be repeated over and over and over in the same parameters with the same results. IF melatonin had the ability to reduce the amount of the drugs used to treat Cushing's, vets would be telling us to do this, researchers would be telling us to do this, numerous studies would tell us to do this. We are NOT being told this nor are we seeing this in any of the research.
Comparing the abilities of Trilostane and Melatonin to lower cortisol is sort of like comparing the abilities of a ball peen hammer and jack hammer to bust up concrete.

Those 5mg of Trilo will be MUCH more effective than the melatonin can ever be - IF it has any effect at all.
Now consider common sense - if something as benign as melatonin could work on a cush pup, who in the world would use drugs like Trilostane or Lysodren?

We would ALL be using melatonin instead.