B vitamins, particularly biotin and B12, play a direct role in hair follicle health and the cycle of hair growth. Deficiency in these nutrients is a known contributor to hair thinning and shedding. While a B Complex injection is not a standalone treatment for hair loss, addressing an underlying deficiency removes a factor that may be slowing down or undermining results from other hair treatments.

Oral supplements depend on the digestive system to absorb them. An injection delivers the full dose directly into the bloodstream. For people with absorption issues or more significant depletion, the difference in how they feel is often noticeable.