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And yes, you are right

Oral vitamins must get broken down by the GI tract (through stomach, intestines) then go through the liver for metabolizing

These symptoms can be very distressing and can interfere with daily life and the ability to care for oneself

Over-supplementing can be harmful as well, especially for B6, since high doses over time may be linked to nerve damage, and studies show that getting too much of either type of B vitamin may be detrimental to bone health

Li W et al., J Pain Res 2020 Methylcobalamin for post-herpetic neuralgia meta-analysis
What is the subcutaneous dose specifically