When it comes to supplements, taking high doses of vitamin C at the same time as your B12 shot might slightly lower the amount of B12 your body can use, but this is more relevant for oral B12 supplements than injections
Absorption studies comparing injection to drops show that injectable medications maintain stable, therapeutic blood levels for 7 days per dose
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10.1104/pp.110.167510 Plant Physiol
Studying single peptides in isolation provides valuable data about specific pathways, but may not capture the complexity of how these pathways interact in vivo