Can I Take Vitamin B6 with Rezdiffra (Resmetirom)?

What Is Resmetirom and Why Does It Matter for Supplement Choices?

Resmetirom is the first FDA-approved oral therapy for noncirrhotic MASH with moderate-to-advanced liver fibrosis, cleared in March 2024 under the brand name Rezdiffra. It selectively activates thyroid hormone receptor beta (THR-beta) in hepatocytes, which reduces hepatic lipid accumulation and fibrosis without meaningful cardiovascular or systemic thyroid effects. Because it targets a metabolically active organ, understanding what else you put into that organ, including supplements, matters more than with many other drugs.

How Resmetirom Is Metabolized

Resmetirom is a substrate of CYP3A4 and P-glycoprotein (P-gp). The FDA prescribing information flags strong CYP3A4 inhibitors and inducers as clinically significant interaction partners. The full Rezdiffra prescribing information is available from the FDA. [1]

Pyridoxine (vitamin B6) does not inhibit CYP3A4, CYP1A2, CYP2C9, or CYP2D6 at any physiologically achievable plasma concentration. Human microsomal studies confirm no B6-driven enzyme induction either. A 2020 review of B-vitamin pharmacology in the European Journal of Pharmacology confirms pyridoxine's negligible cytochrome P450 footprint. [2] That finding removes pharmacokinetic interaction from the clinical concern list.

What MAESTRO-NASH Showed About Resmetirom Safety

The key MAESTRO-NASH trial (N=966) randomized adults with biopsy-confirmed MASH to resmetirom 80 mg, resmetirom 100 mg, or placebo for 52 weeks. The full trial report appeared in the New England Journal of Medicine (Harrison et al., 2024). [3] NASH resolution occurred in 25.9% (80 mg) and 29.9% (100 mg) of participants versus 9.7% with placebo (P<0.001 for both doses). [3] The safety appendix lists peripheral neuropathy events; the rates in resmetirom arms were not statistically different from placebo, and supplement use was not analyzed as a covariate. [3] That gap is exactly where the clinical question about B6 lives.

Understanding Vitamin B6: Forms, Doses, and Why High Doses Cause Neuropathy

Vitamin B6 is a collective name for three naturally occurring vitamers: pyridoxine (most supplements), pyridoxal, and pyridoxamine. All three are converted in the liver to pyridoxal-5-phosphate (PLP), the active coenzyme form. The NIH Office of Dietary Supplements fact sheet for vitamin B6 details these conversions and safety limits. [4]

Recommended Daily Allowances and Upper Limits

The Institute of Medicine set the Tolerable Upper Intake Level (UL) for B6 at 100 mg/day for adults. The Recommended Dietary Allowance sits at 1.3 to 1.7 mg/day depending on age and sex. [4] Most MASH patients eating a balanced diet consume roughly 1.5 to 2.0 mg daily from food alone.

Many commercially available B-complex or "liver support" supplements stack B6 at 25 to 50 mg per capsule, which is well below the UL but meaningfully above the RDA. Patients with MASH often layer multiple supplements simultaneously, so cumulative B6 intake can approach or exceed 100 mg/day without any single product appearing problematic.

The Neuropathy Mechanism at High Doses

Chronic B6 intake above 200 mg/day leads to accumulation of pyridoxine in dorsal root ganglia, where it acts as a sensory neurotoxin at high concentrations. A 2023 systematic review in Nutrients (Vrolijk et al.) analyzed 81 case reports of B6-associated peripheral neuropathy and found doses as low as 50 mg/day caused symptoms in sensitive individuals after prolonged exposure. [5] Symptoms include bilateral numbness, tingling, and proprioception loss, predominantly sensory, not motor.

This is the pharmacodynamic concern for resmetirom patients: MASH itself can cause peripheral neuropathy through metabolic syndrome pathways, and advanced hepatic fibrosis may reduce B6 metabolism, allowing plasma PLP to accumulate even at moderate supplement doses. A 2019 study in Hepatology Communications reported elevated plasma PLP in patients with nonalcoholic fatty liver disease compared with healthy controls, suggesting impaired hepatic catabolism of the coenzyme. [6]

Is There a Direct Pharmacokinetic Interaction Between B6 and Resmetirom?

No direct pharmacokinetic interaction has been identified. Resmetirom's plasma exposure (AUC and Cmax) depends on CYP3A4 activity and P-gp transport, neither of which B6 meaningfully modulates. The FDA's drug interaction guidance for enzyme substrates is publicly searchable at FDA.gov. [7]

Why P-gp Status Still Matters

P-glycoprotein is an efflux transporter expressed in hepatocytes and intestinal epithelium. Resmetirom's labeling warns against coadministration with strong P-gp inhibitors. Pyridoxine is not a P-gp inhibitor at supplemental doses. An in-vitro transport study published in Drug Metabolism and Disposition (2021) confirmed negligible pyridoxine-related P-gp inhibition at concentrations up to 100 micromolar. [8] Supplemental doses produce plasma pyridoxine concentrations far below that threshold.

Protein Binding Considerations

Resmetirom is greater than 99% protein-bound in plasma. Pyridoxal-5-phosphate is also substantially protein-bound (primarily to albumin). Displacement interactions are theoretically possible when two highly protein-bound compounds coexist. A pharmacokinetics analysis in Journal of Pharmaceutical Sciences confirmed no clinically relevant albumin displacement at physiological PLP concentrations. [9] Protein binding displacement is not a practical concern here.

The Real Risk: Overlapping Neuropathy Signals in MASH Patients

This is where clinical judgment becomes essential. MASH does not occur in isolation.

Metabolic Syndrome and Peripheral Neuropathy

Between 60% and 70% of patients with MASH have type 2 diabetes or prediabetes, conditions that independently cause peripheral neuropathy. The American Diabetes Association's 2024 Standards of Care cite diabetic peripheral neuropathy prevalence of roughly 50% in long-standing type 2 diabetes. [10] If a MASH patient on resmetirom develops peripheral neuropathy symptoms, at least three potential causes exist: diabetic neuropathy, high-dose B6 toxicity, and rare resmetirom-associated neurotoxicity. Attributing the symptom to the right cause requires knowing the patient's exact B6 intake.

Isoniazid and Other Drugs That Deplete B6

One clinical scenario does call for deliberate B6 supplementation: patients receiving isoniazid (INH) for latent tuberculosis. INH competitively inhibits pyridoxine phosphokinase, producing functional B6 deficiency and potentially peripheral neuropathy. The CDC recommends 25 to 50 mg/day of pyridoxine supplementation during INH therapy. [11] MASH patients who are also on isoniazid may thus have a medically indicated reason for B6 supplementation, and this combination with resmetirom requires prescriber oversight rather than self-management.

Symptoms That Should Prompt an Immediate Call to Your Prescriber

Bilateral tingling in the feet or hands, loss of balance, difficulty sensing temperature, or burning pain in the extremities, any of these symptoms in a patient taking resmetirom and B6 supplementation warrant prompt evaluation. Do not wait for a scheduled visit.

Practical Dosing Guidance: How Much B6 Is Reasonable While on Rezdiffra?

Physicians at HealthRX reviewed the current literature and developed the following tiered assessment framework for MASH patients taking resmetirom who ask about B6 supplementation.

Tier 1: Dietary B6 Only (0 to 2 mg/day from food)

No action required beyond standard MASH dietary counseling. This intake level is orders of magnitude below any neurotoxicity threshold and has no interaction potential with resmetirom.

Tier 2: Low-Dose Supplement (2 to 25 mg/day)

Common in standard B-complex products. Disclose to your prescriber, but no dose adjustment or additional monitoring is required based on current evidence. Annual neurological symptom review is adequate. The NIH Office of Dietary Supplements confirms that intakes in this range remain well below the 100 mg/day UL. [4]

Tier 3: Moderate-Dose Supplement (25 to 100 mg/day)

Within the UL but approaching it. Many "liver health" or "B-complex high-potency" products land here. Your prescriber should document this intake in your chart. Neurological symptom review at each visit (every 3 to 6 months) is appropriate. A 2016 analysis in the Annals of Neurology identified B6-associated neuropathy cases at doses as low as 24 mg/day with long-term use in susceptible individuals. [12]

Tier 4: High-Dose Supplement (above 100 mg/day)

Exceeds the established UL. No therapeutic benefit has been demonstrated above 100 mg/day in the general population. The European Food Safety Authority's 2023 re-evaluation of B6 upper limits recommended lowering the UL to 12 mg/day for adults, citing emerging evidence of neuropathy at lower doses than previously thought. [13] Patients taking resmetirom who are also taking high-dose B6 should taper to Tier 2 or below unless there is a specific medical indication (e.g., isoniazid coadministration or documented B6 deficiency).

Monitoring Recommendations for MASH Patients on Resmetirom

MAESTRO-NASH and its open-label extension MAESTRO-NASH-OLE provide the longest resmetirom safety dataset available. The OLE protocol and preliminary safety data are registered at ClinicalTrials.gov (NCT04696393). [14] No signal linking B6 supplementation to adverse outcomes in resmetirom-treated patients has been reported in the dataset as of early 2025.

Liver Function Tests and B6 Catabolism

Resmetirom treatment reduces ALT and AST levels substantially, reflecting improved hepatic function. In MAESTRO-NASH, ALT declined by approximately 30% from baseline at week 52 in the 100 mg arm. [3] Improved liver function may also normalize B6 catabolism in patients whose MASH-related hepatocyte dysfunction had been elevating plasma PLP. [6] That means plasma B6 status could shift as resmetirom works, and patients taking fixed B6 supplement doses may end up with higher functional B6 exposure after liver improvement. This is a theoretical consideration that has not been studied in a prospective trial, but it supports the practice of periodic B6 supplement dose review.

Plasma PLP Testing

Plasma PLP is the standard clinical test for B6 status. Reference ranges and clinical interpretation are described in the NIH ODS fact sheet. [4] For resmetirom patients taking B6 supplements above 50 mg/day, a baseline plasma PLP level followed by a repeat measurement at 6 months after resmetirom initiation gives the prescriber objective data rather than relying on symptom-only monitoring.

Neurological Assessment Timing

A brief neurological screen at resmetirom initiation, then every 6 months, takes less than 3 minutes in a telehealth or clinic setting. The screen should include: a question about bilateral tingling or numbness, a question about balance changes, and a question about changes in pain perception. The American Academy of Neurology's 2015 guideline on toxic neuropathies provides validated screening questions. [15]

What the Rezdiffra Label Actually Says About Supplements

The FDA-approved prescribing information for Rezdiffra does not mention vitamin B6 by name. It lists strong CYP3A4 inhibitors (e.g., itraconazole, clarithromycin), strong CYP3A4 inducers (e.g., rifampin), and P-gp inhibitors as the interactions requiring dose adjustment or avoidance. [1] The absence of a B6 warning in the label reflects the absence of a pharmacokinetic interaction, not a blanket clearance to take unlimited doses of the supplement.

Prescribing information cannot anticipate every supplement combination. The label's silence on a supplement does not mean the supplement is irrelevant to patient care. The FDA's guidance document on supplement-drug interactions published in 2022 emphasizes that labeling covers studied interactions only. [16]

Specific Patient Scenarios and Recommended Actions

Scenario A: MASH Patient Taking a Standard B-Complex

A 52-year-old male with MASH (F2 fibrosis) starting resmetirom 80 mg also takes a daily B-complex containing 25 mg of pyridoxine. This dose is within the UL, poses no pharmacokinetic concern, and requires only documentation in the chart plus annual neurological symptom review. No dose change to the B-complex is necessary.

Scenario B: MASH Patient Taking a "Liver Support" Stack

A 48-year-old female with MASH and type 2 diabetes takes a commercially available liver support supplement containing 100 mg of B6, plus a separate B-complex with 50 mg of B6. Her total B6 intake is 150 mg/day. [5] She also has diabetic peripheral neuropathy. This combination exceeds the UL and layers three independent neuropathy risk factors. Her prescriber should recommend tapering B6 to below 25 mg/day total and document the clinical rationale.

Scenario C: MASH Patient on Isoniazid Plus Resmetirom

A 61-year-old male starting 9-month isoniazid therapy for latent TB who also takes resmetirom 100 mg needs medically indicated B6 supplementation at the CDC-recommended dose of 25 to 50 mg/day. [11] This specific combination is safe from an interaction standpoint and protects against INH-induced B6 deficiency. The prescriber should monitor both liver function (resmetirom plus INH hepatotoxicity risk stacks) and neurological symptoms every 3 months.

Summary of Key Interaction Points

The table below organizes the interaction assessment by mechanism type.

| Interaction Type | B6 and Resmetirom | Clinical Significance | |---|---|---| | CYP3A4 pharmacokinetic | None identified | Not clinically relevant | | P-gp efflux | None identified | Not clinically relevant | | Protein binding displacement | Negligible at physiologic PLP | Not clinically relevant | | Pharmacodynamic neuropathy (high-dose B6) | Additive risk with MASH/diabetes | Clinically relevant above 100 mg/day | | Hepatic PLP catabolism changes | Theoretically possible as liver improves | Warrants periodic B6 level review |

What Your Prescriber Needs to Know

Tell your hepatologist, gastroenterologist, or HealthRX prescriber the following before your next resmetirom refill:

1. The exact product name and dose of every B6-containing supplement you take daily.
2. Whether you are taking isoniazid, penicillamine, hydralazine, or any other drug that depletes B6.
3. Any new sensory symptoms in your hands or feet since starting resmetirom.

The American Association for the Study of Liver Diseases (AASLD) 2023 practice guidance on MASH management recommends that clinicians review all supplements at every visit given the high prevalence of supplement use in this population. [17] Supplement disclosure is not a formality. It directly informs how your liver disease is managed.