If you take 250 mg of vitamin B6 orally as film-coated tablets, how long does it take until the greatest portion of it reaches the brain? When does the peak occur and how does the substance spread? Are there easy ways to extend this time by one hour by e.g. eating or drinking?

EDIT: Some words on my motivation. I'm trying to do the experiment described at the Wiki page on Vitamin B6, which says that B6 increases the ability for dream recall.

  • Nice, and indepth, however, not being a biologist nor a science major, to reword it, you seem to be saying it takes about 1 to 2 hours to feel the effect on the brain. For example, for people who take it for ADHD, that want more dopomine, might be getting a bit more dopomine after an hour or so. You also have noted that if we have food in our system, that it might slow down the absorption. Thanks. I will take it on an empty stomach, and wait about an hour to see if this helps the vitamin to do it's thing. Sorry for the layperson's "terminology" but I want to make sure we are both in agreement
    – Cathy
    Commented May 15, 2020 at 15:17
  • @cathy I think the accepted answer covers yours as well
    – draks ...
    Commented May 16, 2020 at 7:45

1 Answer 1


The medical way to ask your question is "What are the pharmacokinetics of pyridoxine (B6 version that you're likely to take)?"

Then that brings us to both primary and secondary sources, along with a good animal model study.

"The greatest portion reaches the brain" will likely be shortly after the peak serum concentration, or Cmax. The amount of time it takes for a drug to get to Cmax is Tmax. There is going to be some variability in Tmax based on age, sex, weight, diet, and B6 formulation. A comparison of two formulations directly found a range of 1.25 to 1.44h, which is a little tighter of the general range of 1-2 hours.

I didn't find a source that showed peak concentrations in CNS tissue or that looked at the delay in B6 crossing the blood brain barrier (which it will readily given its solubility), but there is little reason to suspect that it is too delayed thereafter. Animal studies have shown that the vast majority (80-90%) of B6 is stored in muscles and the liver, so even though the peak concentration for the CNS will follow Cmax, most of the B6 will not end up there.

Your next two questions are mostly implicitly answered in the first question. The peak and greatest portion are likely to be very close together (I couldn't find any evidence of delayed metabolism in the CNS). But expanding on your third question a little, it gets there via the blood, which is pretty standard for most drugs/nutrients/vitamins in humans. As far as taking it from swallowing the pill, it then continues along the digestive tract to the small intestine. Mostly in the jejunum, but somewhat in the ileum (2nd and 3rd part of small intestine) it passively diffuses into the blood, where it circulates through the heart and eventually to your brain.

Eating more food may prolong the time the pill is in the stomach, thereby delaying the time that the B6 is absorbed in the small intestine. Generically this is called gastric emptying, and an approachable site on the subject can be found here. Even though I'm pretty sure this is made up data to estimate the point, I think it's worth duplicating their time graph:

%meal in stomach vs time

I would like to point out, that this is not something that you will be able to time on a stopwatch and fine tune. Any of these values could easily vary by an hour. I also want to point out that taking high doses of B6 can be habit forming, and that the study on dreaming cited in the wiki is far from convincing. Further it was published in a relatively low impact journal. I'm not saying it isn't true, but I don't like the idea of people super dosing B6 for recreational dream use.

  • +1, thanks. You say that high doses can be addictive. are there studies on this?
    – draks ...
    Commented Sep 18, 2015 at 6:35
  • I will see what I can find for primary sources, but here's a generic reference. To help the lay prospective I will reword that to habit forming.
    – Atl LED
    Commented Sep 18, 2015 at 12:28
  • In your reference they call it B6 dependency. Any idea how serious this is?
    – draks ...
    Commented Sep 18, 2015 at 12:41
  • Well in the worse case you're talking about seizures from withdrawal, but that isn't too likely. You would want to get with a physician and work out a step down program.
    – Atl LED
    Commented Sep 18, 2015 at 17:36
  • @draks... Here is a good compilation of effects from B6 toxicity. I'm still going over primary lit and found plenty of examples of lowered concentrations following prolonged use, and as in that link, plenty on where it can go wrong with taking to much. The article that has 33 day dependency is from a journal that doesn't electronical archive back to 1985 when it was published, so I'm going to see if I can get my hands on a print copy.
    – Atl LED
    Commented Sep 19, 2015 at 2:17

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