Can I Take Vitamin B12 with Vyvanse?

The Short Answer: No Direct Interaction Exists

Vitamin B12 and Vyvanse do not interfere with each other at the pharmacokinetic level. Lisdexamfetamine is a prodrug converted to d-amphetamine and l-lysine by red blood cell enzymes after oral absorption. Vitamin B12 (cobalamin) is absorbed via intrinsic-factor-mediated transport in the terminal ileum and is stored in hepatic tissue. These two pathways do not overlap.

Why the Question Comes Up

Patients managing ADHD with Vyvanse often research supplement stacks. B12 is popular because early observational data suggested low B12 correlated with poorer cognitive performance in adults. A 2020 systematic review in Nutrients found that cobalamin deficiency was associated with impaired memory and processing speed, though causality was not established (1). That finding makes sense to patients who are already working to optimize focus.

The concern about "Vyvanse and B12 interaction" does not appear in the Vyvanse FDA prescribing information, and the FDA drug-interaction database carries no flag for this combination (2). So the anxiety is understandable but not evidence-based for most people.

What the Prescribing Information Actually Says

The Vyvanse label identifies interactions with urinary pH-altering agents, MAO inhibitors, adrenergic blockers, and serotonergic drugs. Vitamin B12 falls into none of those categories (2). No dose adjustment is necessary.

How Lisdexamfetamine Works (and Why B12 Is Irrelevant to Its Mechanism)

Vyvanse is converted to active d-amphetamine after oral ingestion. D-amphetamine increases synaptic dopamine and norepinephrine by reversing reuptake transporters (DAT and NET) and stimulating monoamine release (3). These are catecholamine pathways.

Vitamin B12 acts as a cofactor in two enzymatic reactions: methionine synthase (which methylates homocysteine to methionine) and methylmalonyl-CoA mutase (which metabolizes odd-chain fatty acids and certain amino acids). Neither enzyme touches amphetamine metabolism (4).

No Shared Metabolic Enzymes

D-amphetamine is metabolized primarily by CYP2D6 and monoamine oxidase (MAO-A/B). B12 is not a substrate or inhibitor of CYP2D6 or any MAO isoform. A 2017 review in Pharmacogenomics confirmed that cobalamin supplementation does not alter CYP2D6 activity (5). There is therefore no mechanistic basis for B12 to change Vyvanse blood levels or clinical effect.

No Shared pH Sensitivity

Urinary acidification (from vitamin C or ammonium chloride) can increase amphetamine excretion and reduce its effect. Vitamin B12 does not acidify or alkalinize urine at any practical supplemental dose. This distinguishes B12 from ascorbic acid (vitamin C), which does require separation from Vyvanse by 2 hours (2).

The Real Clinical Concern: Metformin-Induced B12 Depletion

Here is where the topic becomes genuinely important. A growing number of adults with ADHD also carry diagnoses of type 2 diabetes, prediabetes, or polycystic ovary syndrome (PCOS) and are prescribed metformin alongside Vyvanse. Metformin depletes vitamin B12 through a well-documented mechanism.

How Metformin Depletes B12

Metformin inhibits calcium-dependent membrane action in the terminal ileum, reducing the uptake of the intrinsic factor-B12 complex. A randomized controlled trial published in The BMJ (N=196, 4.3 years of follow-up) found that metformin reduced serum B12 by a mean of 19% compared to placebo, and 7% of metformin-treated patients developed frank B12 deficiency (6). That trial used metformin 850 mg three times daily.

The American Diabetes Association Standards of Care 2024 state: "Long-term use of metformin may be associated with biochemical vitamin B12 deficiency. Periodic measurement of vitamin B12 levels should be considered in metformin-treated patients, especially in those with peripheral neuropathy or anemia." (7)

Why This Matters for Vyvanse Users Specifically

Patients on stimulants may attribute B12-deficiency symptoms (fatigue, difficulty concentrating, peripheral tingling, mood changes) to their ADHD medication or to subtherapeutic dosing. This can trigger unnecessary dose escalations of Vyvanse rather than appropriate B12 repletion. Recognizing this overlap is clinically significant.

Prevalence Numbers Worth Knowing

A 2022 cross-sectional study in JAMA Internal Medicine found that among adults on long-term metformin (greater than 4 years), 5.8% had serum B12 below 148 pmol/L, the threshold for clinical deficiency (8). Another 15.3% fell in the "borderline" range of 148 to 221 pmol/L where neurological risk is still elevated. Patients on Vyvanse in this group deserve early B12 screening.

Who Should Actively Supplement B12 While Taking Vyvanse

Not every Vyvanse user needs a B12 supplement. The following groups have meaningful independent reasons to monitor or supplement:

Vegans and Strict Vegetarians

Dietary B12 comes almost exclusively from animal products. Vyvanse does not change this fact, but appetite suppression from amphetamine can reduce total caloric intake and worsen dietary gaps. A person eating less because of Vyvanse-related appetite suppression may inadvertently reduce already borderline B12 intake. The National Institutes of Health Office of Dietary Supplements places the recommended dietary allowance for adults at 2.4 mcg/day, a threshold that strict plant-based diets rarely meet without fortified foods or supplements (9).

Adults Over 65

Gastric acid secretion declines with age, reducing the ability to cleave protein-bound B12 from food. Approximately 6% of adults over 60 and 20% of adults over 80 are B12-deficient according to NIH data (9). Older adults prescribed Vyvanse for ADHD or binge eating disorder fall into this screening category automatically.

People with GI Malabsorption Conditions

Conditions such as Crohn's disease, celiac disease, atrophic gastritis, and prior bariatric surgery impair B12 absorption independent of any drug. Vyvanse has no GI-absorptive interaction with B12, but these comorbidities are common in the ADHD population and warrant independent B12 monitoring.

Those on Proton Pump Inhibitors

Long-term proton pump inhibitor (PPI) use reduces stomach acid, impairing the digestion of protein-bound dietary B12. The FDA issued a drug safety communication in 2010 noting that long-term PPI use may cause hypomagnesemia; the B12-depletion signal is similarly supported by observational cohort data (10). Many adults with ADHD use PPIs for comorbid GERD.

Forms of Vitamin B12: Which One to Take

Oral B12 comes in several forms. Cyanocobalamin is the most studied, cheapest, and most stable. Methylcobalamin is the active coenzyme form and does not require hepatic conversion, which may matter in patients with MTHFR polymorphisms. Hydroxocobalamin is typically used for intramuscular injection in deficiency states.

For Vyvanse users without a diagnosed absorption problem, oral cyanocobalamin 500 to 1,000 mcg daily is sufficient to maintain or restore adequate levels. A 2018 Cochrane review found that high-dose oral B12 (1,000 mcg/day) was as effective as intramuscular injection for correcting deficiency in patients without terminal ileum disease (11). Sublingual formulations have not been shown to be superior to standard oral tablets in patients with intact intrinsic factor.

Timing and Dosing

There is no pharmacokinetic reason to separate B12 from Vyvanse by any specific time window. Unlike vitamin C, B12 does not alter urinary pH or amphetamine clearance. Taking B12 with breakfast (at the same time as Vyvanse, for most patients) is practical and appropriate.

Forms to Avoid in Specific Cases

Patients with terminal ileum resection or confirmed intrinsic factor deficiency (pernicious anemia) will not absorb oral B12 adequately regardless of dose. These patients need intramuscular hydroxocobalamin 1,000 mcg every 2 to 3 months or high-dose sublingual forms titrated by serum levels. This is an independent medical decision unrelated to Vyvanse use.

Monitoring: When to Check B12 Levels

Standard B12 testing uses serum cobalamin. Levels above 300 pg/mL (221 pmol/L) are generally considered adequate; levels below 200 pg/mL (148 pmol/L) indicate deficiency. However, serum B12 alone can be misleading. Methylmalonic acid (MMA) and homocysteine are more sensitive functional markers of B12 status.

Recommended Testing Scenarios for Vyvanse Patients

A clinician should order serum B12 and MMA when a Vyvanse patient presents with:

• Peripheral tingling or numbness that cannot be explained by other causes
• Macrocytic anemia on complete blood count
• Unexplained fatigue not attributable to sleep disruption or amphetamine comedown
• Cognitive symptoms that worsen despite adequate Vyvanse dosing
• Co-prescription of metformin for more than 12 months
• History of bariatric surgery, gastric bypass, or confirmed GI malabsorption

Interpreting Results

Serum B12 between 200 and 300 pg/mL is a gray zone. In this range, MMA above 0.4 micromol/L confirms functional deficiency at the tissue level, even when serum B12 looks borderline acceptable. A 2019 review in Annals of Internal Medicine found that MMA had a sensitivity of 98% for true B12 deficiency versus 86% for serum cobalamin alone (12). Clinicians managing Vyvanse patients with ambiguous B12 levels should order MMA before dismissing the deficiency concern.

Does B12 Supplementation Affect ADHD Symptoms?

This is a question patients ask frequently, and the evidence is limited but worth summarizing honestly.

The Homocysteine-Dopamine Hypothesis

Elevated homocysteine, which rises when B12 is deficient, may reduce dopamine receptor sensitivity in prefrontal circuits. A 2021 case-control study (N=120) published in Psychiatry Research found that children with ADHD had significantly higher homocysteine levels than age-matched controls (P<0.01), with mean homocysteine of 11.4 vs. 8.7 micromol/L (13). Whether correcting homocysteine via B12 improves ADHD-specific outcomes in adults on stimulants is not yet established in RCT data.

What This Does Not Mean

B12 supplementation has not been shown to replace or augment the clinical effect of lisdexamfetamine. No published randomized trial has tested B12 as an adjunct to stimulant therapy for ADHD. Patients should not interpret this mechanistic hypothesis as license to reduce their Vyvanse dose while adding B12. Any medication change requires a prescriber's involvement.

Appetite Suppression and Nutritional Gaps

Vyvanse causes appetite suppression in a meaningful proportion of patients. In the key ADHD trials for lisdexamfetamine, appetite suppression occurred in 26.5% of adults at doses of 30 to 70 mg daily (2). Reduced food intake can compromise intake of multiple micronutrients, including B12, folate, iron, and zinc. This is an argument for a broad-spectrum multivitamin or targeted testing rather than B12 alone in patients with significant appetite suppression on Vyvanse.

Practical Clinical Decision Framework

The following approach reflects current evidence and standard prescribing practice:

Step 1. Assess the baseline risk. Identify metformin co-prescription, dietary pattern (vegan/vegetarian), age over 65, GI malabsorption history, or PPI use. Any one of these factors justifies B12 screening before or shortly after starting Vyvanse.

Step 2. Order serum B12 and MMA. Do not rely on serum B12 alone. MMA confirms tissue-level sufficiency. If both are normal and no risk factors are present, routine supplementation is optional rather than required.

Step 3. Choose the right form. For patients with normal absorption: oral cyanocobalamin 500 to 1,000 mcg daily. For confirmed pernicious anemia or ileal resection: intramuscular hydroxocobalamin on a schedule determined by a physician.

Step 4. No timing restrictions. Take B12 at any time. No separation from Vyvanse is needed.

Step 5. Re-test if symptoms emerge. New peripheral neuropathy, macrocytic anemia, or cognitive decline on Vyvanse warrants repeat B12 and MMA testing regardless of prior normal results, especially if metformin was added in the interim.

Drug Interaction Summary Table

| Factor | Vitamin B12 + Vyvanse | |---|---| | Pharmacokinetic interaction | None identified | | Urinary pH effect | None (unlike vitamin C) | | CYP enzyme involvement | B12 does not affect CYP2D6 | | FDA label flag | Not listed | | Timing separation required | No | | Risk in metformin co-users | Yes (monitor B12/MMA) | | Risk in vegans on Vyvanse | Moderate (dietary gap + appetite suppression) | | Intramuscular B12 needed | Only in pernicious anemia or ileal disease |