It was during cancer surgeries and therapies, and recommended to me by the hospital + various specialist doctors, so that's the only vote of confidence I needed that it was OK.
I had no side effects while on it, didn't lose or gain weight, and actually quite enjoyed not having to worry about shopping, cooking, washing up, etc. I also slept better, and all-round "felt" better.
I've considered trying it longer term voluntarily, maybe try 6 months or so, and get the full gamut of medical tests done before and after, to see what they say.
[1] http://www.sustagen.com.au/products/sustagen-hospital-formul...