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Other relevant interactions: Colchicine (used for gout) may affect B12 absorption with long-term use Chloramphenicol (rarely used antibiotic) may blunt the haematological response to B12 treatment Monitoring considerations: Patients taking loop or thiazide diuretics require careful monitoring when initiating B12 therapy in severe deficiency, due to the risk of hypokalaemia during rapid cell production

That is 20 weeks at the starting dose, or 10 weeks if you have titrated up to 0.5mg

My wifes serum B12 levels are above average to high (737 to 1,484), yet she is B12 deficient

[14] A dose of 200 mcg per day has been found to reduce TPO antibodies by about 50 percent within three months