Parasym Plus is most effective in stimulating the vagus nerve if you take two on an empty stomach first thing in the morning. Rapid absorption is key when trying to stimulate the nerve. Everyone is different, but I was one with severe histamine problems and didn’t have a problem with apple cider vinegar — our sensitivities can be so individual, though. I didn’t want to have liquid going down my esophagus every day, though, and Betaine was too irritating for me. It was a happy compromise. I hope it is hugely helpful for you! 🙂