By Dr. Jefferson Vaughan, MD, FACS — Board-Certified General Surgeon, Founder of WLSVitamins
This is the third article in our series expanding on GLP-1 micronutrient depletion. Of everything we cover in this series, thiamine (vitamin B1) is the one I want patients to take most seriously — not because it's the most common deficiency, but because it can develop the fastest and, left unaddressed, has the most serious potential consequences.
Why thiamine is different from other nutrient gaps
Unlike fat-soluble vitamins, thiamine has very limited storage in the body — typically only a few weeks' worth. When food intake drops sharply, as it does on GLP-1 medications or immediately after bariatric surgery, thiamine stores can become depleted faster than almost any other nutrient. We've seen this pattern for decades in the early post-operative period after sleeve gastrectomy and gastric bypass, and GLP-1 therapy produces a nutritionally similar state.
Why it's so often missed
Early thiamine deficiency presents with symptoms that are almost identical to common GLP-1 side effects and to weight loss in general:
- Fatigue and general weakness
- Nausea, which can be mistaken for a GLP-1 side effect rather than its cause
- Irritability or mood changes
- Numbness or tingling in the hands or feet
- Difficulty concentrating
Because of this overlap, thiamine deficiency is frequently misattributed to "the medication" rather than identified and corrected. In more advanced, prolonged deficiency, thiamine depletion can progress to more serious neurological symptoms — which is precisely why it deserves more attention than it typically gets in conversations about GLP-1 side effects.
Who is most at risk
- Patients experiencing significant or persistent nausea and vomiting on their GLP-1 medication
- Patients who are eating very little for several consecutive days (illness, aggressive dose titration, etc.)
- Anyone combining a GLP-1 medication with alcohol use, which further depletes thiamine
- Patients who have also had prior bariatric surgery
What we recommend
A standard multivitamin dose of thiamine (around 1.2 mg) is calibrated for a person eating a normal, full diet — not for someone eating 40–60% less food than usual. Bariatric-style protocols typically call for meaningfully higher thiamine intake as a preventive baseline, not just as a treatment after symptoms appear.
Our Daily Multi-Vitamin was formulated with near-therapeutic thiamine dosing specifically because of this pattern — the goal is to prevent the gap before it opens up, not to catch up after symptoms are already present. If you're experiencing persistent nausea, confusion, weakness, or numbness on a GLP-1 medication, this is worth raising with your prescriber promptly rather than waiting it out.
This content is for educational purposes only and does not constitute medical advice. Consult your healthcare provider before beginning any supplement regimen. These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.