My last dog had Cushings disease. I went years with treating her naturally (drenamin -- bovine adrenal extract, milk thistle, colostrum, enzymes, etc.) because, like you, I did not want to give her the drugs that were available because of the side effects. There was one that at the time was new and had to be imported from the UK. It was called Vetory. The drug name is Trilostane. Do some online searches, and I think you will be impressed. I had to fill out forms with vet info to get it imported then. My vet had never heard of it. There were absolutely no side effects (except that it worked and helped the Cushings and her diabetes was better because of Cushings control). After my vet saw the great results in my dog, she started recommending it to her other patients' owners.
By the way, the one supplement that I called Chewey's "Miracle Pill" was called Vet-Zymes Formula V4. A vet has to order it. It is basically specific digestive enzymes. Somehow there was a HUGE improvement in her mood, energy, etc. when she took this. I quit giving it to her after the first bottle ran out, because I didn't realize that was what made the difference and I was spending a TON of money on different supplements, tests, vet bills, etc. I noticed a decline pretty quickly when I wasn't giving it to her, and then from that day I made sure she had it every day. You could search online, find the ingredients, and see if you can find a cheaper product with the ingredients that you wouldn't have to go through a vet to get.