Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate. The effectiveness ratings for THIAMINE are as follows:

Effective for…

  • Thiamine deficiency. Taking thiamine by mouth helps prevent and treat deficiency.

Possibly effective for…

  • Cataracts. High intake as part of the diet is associated with reduced odds of developing cataracts.
  • Kidney damage in people with diabetes (diabetic nephropathy). Early research shows that taking high-dose thiamine (300 mg daily) decreases the amount of albumin in the urine in people with type 2 diabetes. Albumin in the urine is an indication of kidney damage.
  • Menstrual cramps (dysmenorrhea). Taking thiamine seems to reduce menstrual pain in teenage girls and young women.

Possibly ineffective for…

  • Surgery to improve blood flow to the heart (CABG surgery). Some research shows that giving thiamine into the vein before and after CABG surgery does not lead to better outcomes than placebo.
  • Mosquito repellent. Some research shows that taking B vitamins, including thiamine, does not help to repel mosquitos.
  • Blood infection (sepsis). Most research shows that giving it by IV, alone or with vitamin C, does not reduce the risk of dying in people with sepsis.

Insufficient evidence to rate effectiveness for…

  • Cancer of the cervix. Increased intake of thiamine and other B vitamins is linked with a decreased risk of precancerous spots on the cervix.
  • Depression. Early research shows that taking it daily along with the antidepressant fluoxetine may reduce symptoms of depression faster than taking fluoxetine alone. People taking thiamine showed more improvements after 6 weeks. But after 12 weeks, symptoms were the same for those taking thiamine or placebo.
  • Dementia. Taking thiamine is linked to a reduced risk of dementia in people with alcohol use disorder.
  • Heart failure. People with heart failure are more likely to develop thiamine deficiency. Some research shows that taking extra might slightly improve the function of the heart. Bu it doesn’t seem to help people who suddenly develop heart failure and don’t have thiamine deficiency.
  • Shingles (herpes zoster). Injecting it under the skin seems to reduce itch, but not pain, in people with shingles.
  • Prediabetes. Early research shows that taking it by mouth helps decrease post-meal blood sugar levels in people with prediabetes.
  • Aging.
  • AIDS.
  • Alcoholism.
  • Brain conditions.
  • Canker sores.
  • Chronic diarrhea.
  • A mental state in which a person is confused and unable to think clearly.
  • Heart disease.
  • Poor appetite.
  • Stomach problems.
  • Stress.
  • Ulcerative colitis.
  • Other conditions.

More evidence is needed to rate thiamine for these uses.

Side Effects Of Thiamine

  • When taken by mouth: LIKELY SAFE when taken by mouth in appropriate amounts, although rare allergic reactions and skin irritation have occurred.
  • When given by IV: LIKELY SAFE when given appropriately by a healthcare provider. Thiamine injection is an FDA-approved prescription product.
  • When given as a shot: Thiamine is LIKELY SAFE when given appropriately as a shot into the muscle by a healthcare provider. Thiamine shots are an FDA-approved prescription product.

Thiamine might not properly enter the body in some people who have liver problems, drink a lot of alcohol, or have other conditions.

Warnings & Precautions

  • Alcoholism and a liver disease called cirrhosis: Alcoholics and people with cirrhosis often have low levels of thiamine. Nerve pain in alcoholism can be worsened by deficiency. These people might require supplements.
  • Critical illness: People that are critically ill such as those that had surgery might have low levels of thiamine. These people might require supplements.
  • Heart failure: People with heart failure might have low levels of thiamine. These people might require supplements.
  • Hemodialysis: People undergoing hemodialysis treatments might have low levels of thiamine. They might require supplements.
  • Syndromes in which it is difficult for the body to absorb nutrients (malabsorption syndromes): People with malabsorption syndromes may have low levels of thiamine. They might require supplements.

Dosage Of Thiamine

The following doses have been studied in scientific research:


  • For thiamine deficiency: The usual dose is 5-30 mg daily in either a single dose or divided doses for one month. The typical dose for severe deficiency can be up to 300 mg per day.
  • For reducing the risk of getting cataracts: A daily dietary intake of approximately 10 mg of thiamine has been used.
  • For kidney damage in people with diabetes (diabetic nephropathy): 100 mg of thiamine three times daily for 3 months has been used.
  • For menstrual cramps (dysmenorrhea): 100 mg, alone or along with 500 mg of fish oil, has been used daily for up to 90 days.


  • For a brain disorder caused by low levels of thiamine (Wernicke-Korsakoff syndrome): Healthcare providers give shots containing 5-200 mg once daily for 2 days.


Consult your doctor or pharmacist.


All information has been provided courtesy of MedLinePlus from the National Library of Medicine and from the FDA.