Hello @haleakala, Welcome to Connect. I think it's always best to check with your doctor when taking supplements but from what I've read there are no upper limits for Vitamin B12 but there may be interactions with certain medications.

"Health Risks from Excessive Vitamin B12 - The FNB did not establish a UL for vitamin B12 because of its low potential for toxicity [1]. Even at large doses, vitamin B12 is generally considered to be safe because the body does not store excess amounts.

Interactions with Medications - Vitamin B12 has the potential to interact with certain medications. In addition, several types of medications might adversely affect vitamin B12 levels. A few examples are provided below. Individuals taking these and other medications on a regular basis should discuss their vitamin B12 status with their health care providers."
--- Vitamin B12 Fact Sheet: https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/#h8

Mayo Clinic also has some information on B12 that may be helpful here - https://www.mayoclinic.org/drugs-supplements-vitamin-b12/art-20363663.

I'm currently taking 2 mg Vitamin B12 in the morning and the evening which is 4000 mcg daily as part of my neuropathy related supplements. I shared my neuropathy story in another discussion here - https://connect.mayoclinic.org/comment/310341/.

Did your doctor express any concerns about increasing the B12?