Just came across this dutch article (translated to English) about high B12 levels and possible safety issues - stichtingb12tekort.nl/weten...
Lots of interesting facts (with links to the original scientific papers - I do like that) such as...
In 2007 in Japan a group of patients with amyotrophic lateral sclerosis were treated with B12. They received 25,000 ug every day for 4 weeks followed by 50,000 ug every week. Long term survival was better for those who received the B12. (Vitamin B12 metabolism and massive-dose methyl vitamin B12 therapy in Japanese patients with multiple sclerosis. Kira J, Tobimatsu S, Goto I.Intern Med 1994;33(2):82-86)
If your doctor is worried about giving you 1,000 ug every month - give them a copy of this.