@00tmg Welcome to Mayo Connect.
And congratulations on asking the most challenging question of the day so far. Using berberine is a more complicated than many other supplements because it has the potential to interact with many medications - increasing the effect of some, reducing the effectiveness of others.

Any impact on potassium levels has the potential to cause issues with the heart because it is a critical part of the body chemistry that helps in conduction and regulation of the electrical impulses there, along with proper levels of sodium and calcium. That is probably why the doctor recommended stopping when the cause was unknown.

Keep in mind that the study of supplements, exactly how they work and why, their impact on the human body, both short and long term, and their interaction with other drugs and supplements, is in its infancy. Very few full blown scientific studies have been undertaken, complete with human trials and long-term results tracking. I will take a shot at answering this, based on some research on Google Scholar, because berberine is a supplement I considered using to help with total cholesterol and had to reject because it has a negative effect on another medication I use. My husband also considered it for blood sugar management, but it is contraindicated with one or more of his meds as well.

That said, what little research exists actually indicates that berberine is thought to act as potassium modifier at the same time as increasing sodium and calcium blocker. Here is a recent article summarizing the findings of all the quality research studies the authors were able to identify, with citations to all the articles:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8107691/
BUT the paper goes on to say that what was not studied was optimum dosage, long term use or drug interactions, among other details. Also, there have been suggestions by some that you not take berberine full-time - suggesting intervals like 8 weeks on, 4 weeks off, but I did not find evidence to support this.

So...now the questions are -
Was the increased potassium cause by the berberine or something else?
Did your potassium level return to normal after stopping?
If it did, did berberine interact with some medication you were using? you can check here:
https://www.webmd.com/vitamins/ai/ingredientmono-1126/berberine
Or do you have some enzyme deficiency that makes it work differently in your body?
Or was the dose of berberine too high for you? Remember, we each metabolize thing differently.
Finally, can you talk to your doctor about another berberine trial? Maybe with a lower dose or interval dosing?

Thanks for giving me something new to learn!
Sue