New Research Finds Kids Taking Stimulants Have Different B12 Synthesis and Gut Microbiomes
Overview
A 2026 study found that ADHD kids taking stimulants had differences in their gut microbiome and B12 creation. This change was linked to looser stools. The study is a preliminary study with a small cohort. It is unclear if the microbiome changes and B12 production were caused by the stimulants or if the kids taking stimulants were more likely to have issues with B12 production.
A personal note before the research
If you’re like most people, you’re fascinated with the gut-brain axis and what that might mean for you. I am – that’s why I’ve written a lot about it that you can read here! And if you’re like most people with ADHD, you’ve at least tried a stimulant.
Stimulants — especially methylphenidate — are one of the most studied for ADHD and have multiple benefits beyond helping us keep our lives intact. For just a few of these areas that are lesser known, check out my article I co-authored with my friend Ludovico (@brain.curiosities online) on Psychology Today here.
Truthfully, there isn’t much research out there that finds a negative for stimulants. This article, in fact, is one of the first ones I’ve seen where it is connected with a worse metabolic outcome — but even then, it’s likely connected in a different and neutral way. Most studies find improvements in nutrients and nutrient production with stimulants. I want to add this here because I’m inclined to believe that the finding is more that kids who need stimulants are more likely to have worse B12 production than the kids who aren’t yet on stimulants. But, truthfully, we don’t know since there wasn’t a ‘before stimulants’ and ‘after stimulants’ test.
That being said, there were also differences in the gut microbiome itself that were connected with looser stools… so if you’ve been wondering why you get some good bowel movements when you take your meds, keep reading.
Study Design
The 2026 study by Stiernborg et al. investigated a lot of variables. One was if using a probiotic called Synbiotic 2000 could help the gut microbiome in adults and kids with ADHD, which I wrote about here. The other was this part: seeing if there were gut microbiome and B12 synthesis differences with stimulants.
There were 151 total kids and adults with ADHD, with 52 adult controls. The study was cross-sectional, meaning it captured a snapshot in time rather than following participants longitudinally. This design allowed the researchers to compare the gut bacteria of people on medication with those not on medication + with those who didn’t have ADHD, but it cannot prove cause and effect.
They measured many things, from in-depth gut microbiome analysis, to the foods they ate, to their stool consistency, to even different genetic snapshots of B12 synthesis. For anyone who likes the nerdy details, the bacterial DNA was analyzed with shallow shotgun metagenomic sequencing, and data were processed to look at species-level differences and functional gene modules.
Gut Microbiome differences
One of the most notable findings was that children with ADHD taking psychostimulants had higher levels of bacteria from the Prevotella genus compared to children not on medication. Specifically, they had higher levels of the species Prevotella bryantii, Prevotella buccalis, Prevotella corporis, and Prevotella multisaccharivorax. They also found lower levels of the species Peptostreptococcus anaerobius.
Unfortunately, either there weren’t enough adults in one of the categories (stimulants vs unmedicated) or they just didn’t look at the data, so we don’t know if this is the same for adults. However, in the adult sample, they did find that ADHD adults had higher Streptococcus pasteurianus and Lachnospiraceae bacterium 3–1 and lower Bilophila wadsworthia than the adult controls.
Continued below…
What Increased Prevotella Means in Other Research
Prevotella species are known for fermenting dietary fiber and producing short-chain fatty acids (SCFAs), which play roles in gut health and inflammation. AKA—we love them, for the most part. The research is still inconclusive since it’s a new area of study, but generally we see beneficial outcomes with higher prevotella. It’s also connected with eating more plants and following non-Western diets.
That being said, this is likely a large part of why we get the “stimulant shits” (pardon the language). Increased prevotella = your body is ‘better’ at using your fiber = smoother time on the throne. Fun!
B12 Production Differences
Alongside shifts in bacterial populations, the study found that children on psychostimulants had lower abundance of the bacterial gene module M00122, which is responsible for vitamin B12 (cobalamin) synthesis.
Now, if you didn’t know, gut bacteria don’t just help digest food — they also produce vitamins and metabolites that the body relies on. In the case of B12, certain bacteria convert simpler compounds into cobalamin using a multi-step enzymatic pathway. Other nutrients, like vitamin K and some B vitamins, are similarly generated or modified by gut microbes. So, when a key bacterial gene module like M00122 is less abundant, it could mean you aren’t making enough B12.
They did look at B12 levels and found that the kids on stimulants had lower levels of B12… However, after normalizing for supplementation, there wasn’t a significant difference. So, either this reduced gut creation of B12 wasn’t big enough of an issue, or the body adapted and was able to somehow use B12 more effectively in those who used stimulants.
Again, it’s difficult to say for sure. However, at the end of the day,the truth is that people with ADHD tend to have lower levels of B12, and it’s important to check. If you’re curious about what tests I recommend along with optimal levels based on the research, purchase my $5 Adult ADHD Bloodtest Masterlist here!
What It Means for You
This study suggests that psychostimulant medication in children with ADHD might be linked to differences in the gut microbiome and B12-related bacterial activity. Kids on stimulants had higher levels of certain bacteria like Prevotella, and lower abundance of the gene module that helps produce B12. These shifts were also associated with looser stools, even though their food intake was statistically similar.
It’s important to stress that this study can’t prove that the medication caused these changes. It’s possible that children who end up on stimulants already had differences in their microbiome or B12 synthesis. Based on my knowledge of the research, I believe it’s most likely that the stimulant was truly associated with the increase in the prevotella species, but the bacterial B12 gene was likely NOT influenced by the stimulant.
For parents and caregivers, this doesn’t mean stopping medication—but it does mean that it might be beneficial to check their B12 levels. In fact, the differences in the gut microbiome with the stimulants trended more positive.
This article summarizes the research from the aforementioned study and is for educational purposes only. Nothing in this article constitutes medical advice.
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