A very interesting resource, which gave me quite a few ideas to try. Thanks for that.

I will introduce myself elsewhere, but I think I can add one tidbit of information here that I *think* has not been mentioned. (I have read the whole thread)

People often ask about B12 upper limits: therefor it is interesting to know that a common treatment against cyanide poisoning (think people who have been in a fire) is ... B12. I learned about this reading a Dutch forum dedicated to B12. No links, but the treatment is "commercially" available to first response teams and hospitals as the cyaono-kit. It is basically a 5 gram (no typo) IV of hydroxocobalamine. In severe cases the treatment is repeated up to 3 times, which means 15 grams of B12 is forced into the blood stream, binding with the cyanide - B12 has excellent binding to it, ho hum... - and secreting it via the kidneys/urine. Although some possible side effects are mentioned, it is generally considered safe, and if I'm not mistaken the kit is mandatory in ambulances where I live.

Of course, this is an emergency producedure (don't try this at home!), but 15 grams is many thousand times the dose you get with an injection, let alone the 10% or so you ingest when using the oral doses of 1000 or 5000 mcg.

In short: no need to worry about upper limits for most people indeed.

As for me: I didn't know methylcobalamine was available OTC until this week. It makes sense for me to try this and see if this can replace the injections regimen I have followed previously. I have stopped all medication for 6 months to get a baseline reading (B12 now hovering around 400, which is still too low), and the injections are a real hassle. It would be nice if I can back to >1000 readings (like with the injections) just taking the pills.