My TB is eating less now and he's been on GG for 2 weeks, he was literally eating me out of house and home, he ate like he'd been starved and constantly needed to be chewing. He's now eating less and has put some weight on and doesn't grump at me when I make him lift his head to fasten the neck on his rug.
Probably not the answer you were after, do you have lack of appetite?
My guy was on GG once a day and Ranitdine 4 times a day and he started to improve after a week. I cut out all grain and just gave him hay and alfalfa pellets. He did a full 6 week course and he is fine now.
Good luck.