Medications can change the pH of your stomach. For example, Nexium, the purple pill you refer to, reduces stomach acid for those who have acid reflux. Alkaline water and most plant-based foods are slightly basic. Many factors influence the pH of your stomach so definitely pay attention to how you are feeling if you are on either of those medications. Eating plant-based foods is one step you can take to help promote a good pH and a healthy microbiome. If you follow a 100% vegan diet and take metformin, both of those warrant vitamin B12 supplementation.
Hope that helps,
Maggie Neola, RD