If you take a proton pump inhibitor for reflux, metformin for blood sugar, or hormonal birth control, the way your body handles vitamin B12 may be different from what you'd expect. This isn't only a vegan topic. It's a medication topic. And it is a topic for your prescriber, not for a supplement shopping cart.
A note before we start: an earlier version of this article was more confident than the evidence allows. It carried prevalence figures and absorption numbers I can't stand behind, and it pointed you toward a strip instead of toward your doctor. I've rewritten it.
I run a sublingual strip company, so weigh what follows accordingly. What I want to do here is walk through how three commonly prescribed medication classes interact with B12, where the evidence is strong, where it's weaker than the headlines suggest, and what actually makes sense to do about it. Spoiler: the answer starts with a blood test.
Why B12 Is Unusually Fragile
Vitamin B12 absorption is one of the most complicated nutrient pathways in the body. It needs stomach acid to free B12 from food proteins, intrinsic factor (a protein made in the stomach) to bind it, and a receptor system in the last stretch of the small intestine to pull it into the bloodstream. Disrupt any one of those steps and B12 intake and B12 status stop tracking each other.
Three widely prescribed medication classes touch that pathway:
Proton pump inhibitors (PPIs) like omeprazole and lansoprazole, taken by a very large number of people for acid reflux and GERD. Metformin, a first-line treatment for type 2 diabetes and one of the most prescribed drugs in the world. Hormonal birth control, used by a substantial share of women of reproductive age.
Each one touches B12 differently. Only one of the three has strong evidence for real depletion, and I'll be specific about which.
Metformin and the Ileum
This is the best-documented of the three. Metformin is a positively charged molecule, and it appears to interfere with the calcium-dependent uptake of the B12–intrinsic factor pair at the surface of cells in the ileum. The receptor involved — cubilin — needs calcium to work. Metformin appears to change the membrane's surface charge in a way that gets in the way of that step.
The clinical literature on this is real. Systematic reviews have found that a meaningful minority of long-term metformin users show evidence of reduced B12 absorption, and both dose and duration appear to matter — higher daily doses and longer treatment tend to go with lower B12 readings. I'm deliberately not attaching a percentage to that, because the reported figures vary widely depending on the study population and on which cut-off the researchers used to define deficiency, and a single number would misrepresent the spread.
One interesting finding: Bauman et al., writing in Diabetes Care (2000), reported that increased calcium intake restored the ileal uptake pathway that metformin had disrupted. That is a research finding, not an instruction — calcium interacts with other medications and with iron absorption, so it is something to raise with your prescriber rather than to act on from a blog post. (XYNE does not sell a calcium product, so I have nothing to gain by mentioning it.)
The American Diabetes Association recommends periodic B12 monitoring for metformin users. "Recommends monitoring" and "actually gets monitored" are different things in a 15-minute appointment, and that gap is the genuinely useful takeaway here: ask.
PPIs: Acid Suppression Has a Side Effect Nobody Mentions
Proton pump inhibitors work by shutting down the acid pumps in your stomach lining. That's great for reflux. It's less great for B12, because stomach acid is what frees B12 from the food proteins it's attached to. Without enough acid, the B12 in your chicken or eggs stays bound up — never meeting intrinsic factor, never reaching the ileum.
Meta-analyses have found an association between long-term acid-lowering drug use and B12 deficiency, and a 2025 systematic review confirmed the association while noting that the evidence base still needs better-designed prospective studies. Association is not the same as proof of cause, and I'd rather say that plainly than dress it up.
There's an important nuance in the mechanism. PPIs mainly affect food-bound B12. The crystalline B12 used in supplements is already free — it doesn't need stomach acid to be released. So the drug's effect lands hardest on B12 from food. The complicating factor is that many long-term PPI users also have other reasons for reduced absorption (atrophic gastritis, age-related changes in the gut), and older adults are both the group most likely to be on long-term PPIs and the group most vulnerable to low B12 in the first place.
Birth Control and B12: What the Data Actually Shows
Here's where I need to be honest, because the old headline of this article promised something about birth control that the evidence doesn't support.
Yes, people taking oral contraceptives show lower measured serum B12. The decrease is measurable and shows up fairly early in use. But the research strongly suggests this is not true tissue depletion. The fall in serum B12 appears to be driven by changes in the B12 binding proteins (transcobalamin) that the test measures — not by an actual functional shortfall.
A study published in Contraception found that while hormonal contraception lowers measured B12, very few women showed clinical B12 deficiency, and the effect was not clinically significant. An older study in the American Journal of Obstetrics and Gynecology concluded there is "no justification for vitamin B12 supplementation in users of oral contraceptives."
So why mention it at all? Because the measured drop is real, and it matters for reading your labs. If your doctor runs a standard B12 panel without accounting for it, a normal person can look low — or a real problem from another cause can get waved off as "just the birth control." The data matters for interpretation, not for buying a supplement.
I could have left this section out and let you assume birth control depletes B12. It would sell more strips. It just wouldn't be true.
When You're on More Than One
The situation worth flagging isn't any single medication — it's being on several. Someone on metformin for type 2 diabetes and omeprazole for reflux is touching the B12 pathway at two points at once: the PPI on acid-dependent release of food-bound B12, the metformin on ileal uptake of whatever reaches intrinsic factor. Research has found that combining the two carries more risk of low B12 than metformin alone. Add the gradual decline in intrinsic factor production that comes with age, and you have a group of people worth monitoring.
Monitoring. Not self-treating. Which brings me to the part where I have to be careful about my own product.
What Sublingual B12 Can and Cannot Claim
Sublingual B12 is genuinely one of the better-studied topics in this space, and I'm not going to pretend otherwise. Published trials have compared B12 given under the tongue with swallowed and injected B12, and a 2025 systematic review in Frontiers in Pharmacology reported that sublingual B12 performed comparably to intramuscular injection in the populations studied, while being less invasive and cheaper — noting its potential value for people with atrophic gastritis, post-gastrectomy status, or medication-related absorption problems. The mucosal route is real pharmacology, not marketing.
Now the limits, which matter more than the headline:
- Those studies tested their own products, at their own doses, in their own formats — usually a tablet or drop held under the tongue. XYNE has not run absorption testing on its own finished strips. I cannot tell you our product performs the way those trials performed, and I'm not going to imply it.
- A strip that dissolves in about 30 seconds is mostly swallowed. That means most of what's in it takes the ordinary digestive route, the same as a capsule. A fast dissolve means less contact time under the tongue, not more.
- At higher supplemental doses, swallowed B12 also raises levels in most people, because some absorption happens passively regardless of the pathway. A B12 pill is not a bad product.
- I am not going to publish absorption percentages or multipliers comparing routes. The numbers that circulate in this category are copied between marketing pages far more often than they're read in context, and the honest answer is that per-dose comparisons depend on form, dose, and study design.
Our Energy strip contains B12 as methylcobalamin, alongside L-theanine and caffeine from green tea. The dose is on the label. What that strip is for is people who don't want to swallow a capsule. It is not a treatment for a diagnosed deficiency, and I'd rather lose the sale than tell you it is. If you want the form comparison, methylcobalamin vs. cyanocobalamin covers it, and first-pass metabolism explained covers why route matters in general.
What I'd Actually Ask a Doctor
If someone in my family were starting metformin, here's what I'd want them to raise with their prescriber — as questions, not as instructions:
- Should I get a baseline B12 before starting, and how often after that?
- I'm also on a PPI — does that change how often you'd want to check?
- If my result comes back borderline rather than clearly low, what do you want to do?
- If I do need B12, what form and route do you recommend for me specifically?
Low B12 is a diagnosis made with bloodwork, and the follow-up depends on why it's low. That's a clinical judgment. No blog post — including this one — can make it for you.
When a Supplement Is the Wrong Answer
I need to be clear about the limits.
If you have pernicious anemia — an autoimmune condition affecting intrinsic factor — that is managed by a doctor, and B12 injections are a medical treatment. Nothing sold on this site is a substitute for that, or an add-on to it, without your doctor saying so.
If you're experiencing numbness, tingling, difficulty walking, memory or thinking changes, or unexplained fatigue, see your doctor before you order anything. Those can have many causes, several of them serious and time-sensitive. A supplement is not a diagnostic tool and delay can matter.
If your doctor has prescribed B12 in a specific form, don't swap it for something you bought online without telling them. Supplements are for general wellness — they don't replace medical judgment.
And if your B12 is fine, confirmed by lab work, you probably don't need to supplement at all. More isn't better when your levels are adequate. That's not what a marketing team wants me to say, but it's what the evidence says.
The Bottom Line
B12 status isn't only a vegan question. It's also a medication question, and it affects a lot of people on PPIs, metformin, or both — often older adults, often people already managing chronic conditions that eat up their attention and their appointment time.
The medications are there for good reasons, and nobody should stop one over something they read here. The useful move is knowing the interaction exists, asking for the blood test, and letting a clinician interpret it. The sublingual route is real and worth understanding — but for us it's a format for people who don't want to swallow pills, not a fix for a diagnosed deficiency. That distinction is the whole point of this article.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement, especially if you are taking prescription medications.
Frequently Asked Questions
Does metformin affect B12?
Metformin can interfere with calcium-dependent absorption of B12 in the ileum, and systematic reviews have found reduced B12 absorption in a meaningful minority of long-term users, with dose and duration both appearing to matter. Reported figures vary a lot between studies, so ask your prescriber about your own situation rather than relying on a number. The American Diabetes Association recommends periodic B12 monitoring for metformin users.
Do PPIs affect B12?
Long-term PPI use has been associated with a higher risk of low B12 in meta-analyses, though reviewers note the evidence base needs better prospective studies. PPIs suppress the stomach acid needed to free B12 from food proteins. The crystalline B12 used in supplements is already free and doesn't need stomach acid, so the effect lands mainly on B12 from food.
Does birth control deplete B12?
Oral contraceptives lower measured serum B12, but current evidence suggests this reflects changes in B12 binding proteins rather than true tissue depletion. Published studies have found no justification for B12 supplementation specifically because of oral contraceptive use. The measured drop mainly matters for interpreting lab results.
Is sublingual B12 better than swallowed B12?
Sublingual B12 is a well-studied route and published reviews have reported it performing comparably to injection in the populations studied. But those trials used their own products, doses and formats, and XYNE has not tested its own finished strips for absorption. A strip that dissolves in about 30 seconds is mostly swallowed, so much of it takes the ordinary digestive route. Which route is right for you is a question for your doctor, especially if you have a diagnosed deficiency.
Should I stop my medication if I'm worried about B12?
No. Never stop a prescribed medication without consulting your doctor. PPIs, metformin, and birth control are prescribed for important medical reasons. The appropriate response is to discuss B12 monitoring with your prescriber at your next appointment — not to discontinue treatment or to self-treat.
Related Reading
- Methylcobalamin vs Cyanocobalamin: Which B12 Form Should You Take?
- Bioavailability Explained: Why Format Affects What You Absorb
- The Sublingual Mucosa: What 30 Seconds Under Your Tongue Actually Does
- First-Pass Metabolism, Explained Like You're a Smart Friend
- Your Parent Can't Swallow Pills — Here Are the Vitamins They Still Need
- Sublingual vs Oral Supplements: What the Evidence Says
