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Question: I have been having neurological symptoms, and a blood test showed I have toxic levels of vitamin B-6. My multivitamin contains 75 mg of B-6, but this is below the upper limit of 100 mg per day. Could my vitamin contain more than it lists?
Answer: As noted in our B Vitamin Supplements Review, unless you are deficient, you only need to get slightly less than 2 mg of vitamin B6 per day from your diet (including supplements), while the daily upper tolerable intake level (UL) is 100 mg. When you exceed the UL, you start increasing your chances of side effects. [Update: In 2016, the FDA reduced the Daily Value for B-6 to 1.7 mg, but this won't be reflected on most supplement labels until 2018 or 2019.]
Since supplements are required to provide at least 100% of their listed amounts of ingredients at the time you purchase them and, if properly maintained, until a listed expiration date, it is customary and acceptable for companies to put in a bit more (an "overage") than the listed amount of an ingredient to compensate for normal degradation. In fact, according the USP, up to 50% more is permitted for B vitamins.
So, yes, it is possible that your multivitamin provided more than the daily upper limit of vitamin B6 -- putting you at some risk of toxicity. This is because your supplement provided an amount of B6 close to the upper limit (and much more than normally needed) and there is an allowable manufacturing overage, as noted above. However, side effects have generally been reported with daily intakes above 200 mg and, more typically, above 1,000 mg, so it would be unusual for the B6 in your supplement alone (if properly made) to cause the side effects you reported. Foods also contribute B6, but it would also be unusual for any non-fortified food to have put you over the UL since foods naturally rich in B6 (like liver, other meats, potatoes, and bananas) provide about 0.25 to 1 mg of B6 per serving.
Be aware that Europe uses a more conservative daily upper limit (25 mg) than in the U.S.