If you are concerned about needles or have had a sensitive reaction to injections in the past, let the provider know
Timeline for Recovery From B12 Deficiency If you are treating a B12 deficiency, you might ask, How long does it take for vitamin B12 to work
Neurological issues like neuropathy may take longer, up to 3-6 months (Carmel, 2008)
Based on investigational protocol reports and the clinical trial data, most subjects begin to see measurable changes in body composition at 4 to 6 weeks on a consistent daily protocol at 300 mcg
(PubMed) Ravaglia G, Forti P, Maioli F, et al
Not everyone responds to beta-3 pathway stimulation equally genetic variation in beta-3 adrenergic receptors affects individual response