The short answer: same day is fine, different injection sites are required, same syringe is not allowed
The NIH Office of Dietary Supplements, citing Institute of Medicine recommendations, advises that it is advisable for those older than 50 years to meet their RDA mainly by consuming foods fortified with vitamin B12 or a supplement containing vitamin B12. This recommendation reflects the fact that 10 to 30% of older adults lose the ability to efficiently absorb naturally occurring B12 from food
GHK-Cu is particularly relevant for this population because of its documented ability to remodel UV-damaged collagen and activate the skin's antioxidant defenses against ongoing solar damage
What are the potential side effects of Glutathione injections on the skin
doi:10.1007/s00417-005-0108-2
Lancet 376(9742):687697 Hurvitz SA et al (2018) Neoadjuvant trastuzumab, pertuzumab, and chemotherapy versus trastuzumab emtansine plus pertuzumab in patients with HER2-positive breast cancer (KRISTINE): a randomised, open-label, multicentre, phase 3 trial
