Maybe magnesium chloride, or magnesium glycinate/orotate. It could be the taste of the citrate if you are taking it in powder form. I absolutely hate the taste of Epsom Salts but the rewards gained after the flush are too much to stop it, even if it is one of the most vile things I have stomached. Maybe you could try chewing on a cinnemon toothpick to try to balance out the taste after each cup of ES, or try to somehow block out the taste, bc I doubt it's the actual Epsom Salts that are making you throw up but the nauseating taste that lingers in your mouth throughout the night unless you wash out your mouth.