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Vitamin B1 (Thiamine) Side Effects & Safety

Evidence:Strong
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This content is for informational purposes only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease. Individual results may vary — consult your healthcare provider before starting any supplement. Full disclaimer

Safety Profile

Overall safety rating: Generally Safe

Potential Side Effects

  • Very well tolerated at oral doses — no common side effects
  • Rare: allergic reactions with IV thiamine administration
  • Rare: mild GI discomfort at very high doses
  • Warm flushing sensation possible with injectable forms

Drug & Supplement Interactions

  • Loop diuretics (furosemide) increase urinary thiamine excretion — may cause depletion
  • Chronic alcohol use depletes thiamine stores and impairs absorption
  • Antacids may reduce thiamine absorption due to alkaline pH
  • 5-fluorouracil inhibits thiamine phosphorylation

Maximum Dose

Do not exceed: No established upper limit — water-soluble with very low toxicity risk; doses up to 500 mg daily used safely in clinical settings

Full Vitamin B1 (Thiamine) Guide

References

  1. RCTStracke H, Gaus W, Achenbach U, Federlin K, Bretzel RG (2008). Benfotiamine in diabetic polyneuropathy (BENDIP): results of a randomised, double blind, placebo-controlled clinical study. Experimental and Clinical Endocrinology & Diabetes. DOI PubMed
  2. ReviewWhitfield KC, Bourassa MW, Adamolekun B, et al. (2018). Thiamine deficiency disorders: diagnosis, prevalence, and a roadmap for global control programs. Annals of the New York Academy of Sciences. DOI PubMed
  3. RCTSchoenenberger AW, Schoenenberger-Berzins R, der Maur CA, et al. (2012). Thiamine supplementation in symptomatic chronic heart failure: a randomized, double-blind, placebo-controlled, cross-over pilot study. Clinical Research in Cardiology. DOI PubMed
  4. Turkia M (2020). The History of Methylprednisolone, Ascorbic Acid, Thiamine, and Heparin Protocol and I-MASK+ Ivermectin Protocol for COVID-19.. Cureus. DOI PubMed
  5. RCTManzardo AM, Pendleton T, Poje A, Penick EC, et al. (2015). Change in psychiatric symptomatology after benfotiamine treatment in males is related to lifetime alcoholism severity.. Drug and alcohol dependence. DOI PubMed
  6. Himmerich H, Erbguth F (2014). [Nutrition and dietary supplements in psychiatric diseases].. Der Nervenarzt. DOI PubMed
  7. RCTManzardo AM, He J, Poje A, Penick EC, et al. (2013). Double-blind, randomized placebo-controlled clinical trial of benfotiamine for severe alcohol dependence.. Drug and alcohol dependence. DOI PubMed