Any member of the group of 1,3-thiazolium cations that exhibit biological activity against vitamin B1 deficiency in animals. Symptoms of vitamin B1 deficiency include constipation, loss of apetite, fatigue, nausea, delirium, blurry vision and muscle weakness. Severe vitamin B1 deficiency can also lead to a disease known as beriberi. Vitamin B1 consists of the vitamer thiamin and its acid, aldehyde and phosphorylated derivatives (and their corresponding ionized, salt and hydrate forms).