In the UK, the most commonly used form of injectable vitamin B12 is hydroxocobalamin injection
Nordio, M., Basciani, S., & Camajani, E
Deficiency symptoms include fatigue, pale or slightly yellowing skin, shortness of breath, palpitations, diarrhoea, tingling in fingers and toes, and lack of coordination
It also has been linked to influencing other growth pathways, like increasing gene expression for repair and even modulating neurotransmitter systems (dopamine, serotonin, etc., in brain injury models)
Whilst there is evidence that laser light can stimulate hair growth at some wavelengths, the biological mechanism by which it occurs has not been defined and clinical data from large scale, placebo controlled trials is lacking (208-210)
Y., Waingarten, C