The most common side effects with methylthioninium chloride are nausea (feeling sick), abdominal and chest pain, headache, dizziness, tremors, anxiety, confusional state, dyspnoea (difficulty breathing), tachycardia (rapid heartbeat), hypertension (high blood pressure), hyperhidrosis (excessive sweating) and the formation of methaemoglobinaemia. For the full list of all side effects reported with methylthioninium chloride, see the package leaflet.
Methylthioninium chloride Proveblue should not be used in people who may be hypersensitive (allergic) to methylthioninium chloride, or to any other thiazine dyes (a group to which methylthioninium chloride belongs). It must not be used in patients with the following conditions:
glucose-6-phosphate dehydrogenase deficiency G6PD,
methaemoglobinaemia caused by sodium nitrite,
methaemoglobinaemia caused by chlorate poisoning,
deficiency in the enzyme NADPH reductase.