My research led me to Prescript-Assist: https://www.amazon.com/dp/B0049NRWHS. Here's a study validating it for IBS patients: https://www.ncbi.nlm.nih.gov/pubmed/16117982.

I also recommend a gut bacteria test like uBiome to see how it alters your composition. Do a before test, then another one after a month or two of use.