Thiamine (vitamin B1) as an insect repellent: a scoping review

While the desire for systemic repellents is high, ineffective repellents put one at risk of insect-vectored pathogens. Vitamin B1, or thiamine, has been touted as a systemic insect repellent since 1943, and denounced as an ineffective placebo for just as long. This paper presents a scoping review of 104 relevant case reports, research studies, and review articles to trace the evolution of this idea and identify an evidence-based, scientific consensus. Reports of thiamine's systemic repellency are primarily anecdotal and based on uncontrolled trials and/or used bite symptoms as a proxy for reduced biting. Controlled experiments on insect landing and feeding found no evidence of repellency. Of the 49 relevant review papers, 16 insect bite prevention guidelines, and 4 government documents, none after the 1990s claimed thiamine is a repellent. The findings of this review are that thiamine cannot repel arthropods in any dosage or route of administration. Due to limited available evidence, the possibility that thiamine reduces the subjective symptoms of insect bites cannot currently be ruled out. Unfortunately, many medical professionals and travelers today still believe thiamine may be effective despite the evidence stating otherwise. Continued promotion of debunked repellents on the commercial market poses a serious risk in countries with the endemic, mosquito-vectored disease.