I want to add that I tried regular B12 vitamins in the past for a short period of time due to side effects. I probably had side effects because I wasn't absorbing it well, and it didn't improve my lips. I wasn't taking a regular B12 vitamin whenever I had my B12 blood test. I also didn't think it was important for me to take B12 because my blood tests showed a high level of it.
This link might be helpful. The vitamin B12 supplements that I have used in the past contained Cyanocobalamin (synthetic). The one I use now contains Methylcobalamin (natural) and dibencozide, which is also known as adenosylcobalamin.