The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
Avoid in people with a known allergy or sensitivity to any parts in thiamine supplements. Rare, life-threatening allergic reactions have been reported after multiple doses of thiamine injected into the vein, muscle, or skin.
Side Effects and Warnings
Thiamine is likely safe when taken by mouth daily in amounts considered to be RDA: in adults 19 and older, 1.2 milligrams for males and 1.1 milligrams for females; and in pregnant or breastfeeding women of any age, 1.4 milligrams. Thiamine is likely safe in adults as a supplement when taken by mouth daily in doses of 1-2 milligrams. Thiamine is likely safe in people with or at risk of thiamine deficiency, in doses of 50 milligrams taken by mouth daily. The following doses of thiamine are likely safe in children when taken by mouth daily: 0.2 milligrams in infants 0-6 months old; 0.3 milligrams in infants 7-12 months old; 0.5 milligrams in children 1-3 years old; 0.6 milligrams in children 4-8 years old; 0.9 milligrams in children 9-13 years old; 1.2 milligrams in males 14-18 years old; and 1 milligram in females 14-18 years old.
The following doses of thiamine are considered to be possibly safe: 50-100 milligrams taken by mouth daily for 3-6 months; 50-100 milligrams injected into the vein 3-4 times daily; and 5-200 milligrams injected into the muscle in five divided doses over two days.
Thiamine may cause low blood pressure. Caution is advised in people who have low blood pressure or those taking drugs that lower blood pressure.
Caution is advised in people with diabetes or high blood sugar, and in those taking drugs, herbs, or supplements that affect blood sugar or that widen blood vessels.
Use cautiously in breastfeeding women, people who have abnormal heart rates, and those receiving chemotherapy.
Avoid high doses of thiamine injected into the vein or brain. Avoid doses higher than those found in marketed products, unless under the advice of a health professional.
Avoid in people with a known allergy or sensitivity to any parts in thiamine supplements.
Avoid using in the absence of vitamin B6 and nicotinamide, as life-threatening brain damage may occur.
Thiamine may cause drowsiness, excitation, immune changes, increased cancer risk, muscle relaxation, seizures (when injected into the vein or brain), skin irritation (burning or itching), slow heart rate, weight changes, and widened blood vessels.
Pregnancy and Breastfeeding
The RDA for pregnant or breastfeeding women of any age is 1.4 milligrams daily.
There is a lack of scientific evidence on the use of thiamine during pregnancy or breastfeeding. Use cautiously in breastfeeding women.
This evidence-based monograph was prepared by The Natural Standard Research Collaboration