This is the single most counterintuitive thing in nerve supplementation, and it's genuinely worth knowing before you take anything: too much vitamin B6 can cause peripheral neuropathy.
Vitamin B6 (pyridoxine) is essential for nervous system function — involved in neurotransmitter synthesis and myelin maintenance. Deficiency can contribute to nerve problems.
But B6 is unusual among water-soluble vitamins: at sustained high doses it becomes neurotoxic. It can cause a sensory peripheral neuropathy — tingling, numbness and loss of position sense, typically starting in the feet.
In other words, the same symptoms someone might be taking a nerve supplement to address.
B6 toxicity neuropathy is well established in the medical literature, which is why B6 is one of the few vitamins with a defined tolerable upper intake level. The NIH Office of Dietary Supplements sets that at 100 mg per day for adults from supplements.
Cases have been reported at doses above that taken over months to years. Some reports involve doses far higher; others involve more modest amounts taken for extended periods.
Nerve formulas frequently contain B-complex vitamins, and B6 is usually among them. If you're taking a nerve supplement plus a multivitamin plus a B-complex, the amounts stack — and few people add them up.
It also creates a genuinely nasty feedback loop: symptoms don't improve, so you take more, and the extra B6 makes things worse.
B6 toxicity neuropathy generally improves after stopping the excess intake, though recovery can be slow and isn't always complete. Which makes it exactly the kind of problem better avoided than treated.
None of this makes B6 bad — at normal amounts it's essential. It makes unmeasured, stacked, high-dose B6 a real and avoidable risk. See the safety section.
Read next: how to read any nerve label properly.