Can you overdose on vitamins?

Did you know that you can have too much of a good thing? Check this table to understand the possible effects of high dosages of nutrients.

The stated levels are to be used as a guide only as toxicity levels could differ depending on a variety of factors.

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Toxic Dosage

Symptoms and Diseases



No side effects from oral administration at therapeutic doses have been reported


>10 mg

No side effects reported


>2,000 mg

Drowsiness, extreme lethargy, impaired absorption of iron, zinc and manganese, calcium deposits in tissues throughout body, mimicking cancer on X-ray


>300 mg

Orange discoloration of skin, weakness, low blood pressure, weight loss, low white cell count


>50 mg

Dermatitis, intestinal ulcers, kidney and liver impairment


15 mg

Fatigue, poor memory, depression, insomnia, increased production of free radicals, may suppress immune function. Violent vomiting and diarrhea. Cooking acid foods in unlined copper pots can lead to toxic accumulation of copper.

Fluoride, acute

500 mg

Poisons several enzymes, (5,000 mg lethal)

Fluoride, chronic

5 mg

Fluorosis (white patches on teeth), bone abnormalities.

Folic acid

15 mg

Abdominal distention, loss of appetite, nausea, sleep disturbances, may interfere with zinc absorption, may prevent recognition of vitamin B12 deficiency


2 mg

Thyroid impairment, iodine poisoning or sensitivity reaction.


25 mg

Intestinal upset, interferes with zinc and copper absorption, loss of appetite, not safe for those with iron storage disorders such as hemosiderosis, idiopathic hemochromatosis, or thalassemias. Toxic build-up in liver, pancreas, and heart.



Diarrhea at large dosages of poorly absorbed forms (like Epsom salts). Disturbed nervous system function because the calcium-to-magnesium ratio is unbalanced; catharsis, hazard to persons with poor kidney function.


75 mg

Toxicity only reported in those working in manganese mines or drinking from contaminated water supplies, which results in loss of appetite, neurological damage, loss of memory, hallucinations, hyperirritability, elevation of blood pressure, liver damage. Mask-like facial expression, blurred speech, involuntary laughing, spastic gait, hand tremors.

Niacin (B3), acute

100 mg

Transient flushing, headache, cramps, nausea, vomiting

Niacin (B3), chronic

3 gm

Anorexia, abnormal glucose tolerance, gastric ulceration, elevated liver enzymes. Excessive uric acid in blood, possibly leading to gout. See Thiamin.

Pantothenic acid (B5)

High dose

Occasional diarrhea. Increased need for thiamin, possibly causing thiamin deficiency symptoms.


High dose

Distortion of calcium-to-phosphorus ratio, creating relative deficiency of calcium.


High dose

Mental impairment, weakness. Excessive potassium in blood, causing muscular paralysis and abnormal heart rhythms.

Pyridoxine (B6)

300 mg

Sensory and motor impairment. Dependency on high doses, leading to deficiency symptoms when one returns to normal amounts.

Riboflavin B2)


No toxic effects have been noted. See Thiamin.


750 micro gm

Diabetes, garlic-breath odor, immune impairment, loss of hair and nails, irritability, pallor, skin lesions, tooth decay, nausea, weakness, yellowish skin

Thiamin (B1)


No toxic effects noted for humans after oral administration. However, since B Vitamins are interdependent, excess of one may produce deficiency of others.

Vitamin A, acute (infant)

75,000 IU

Anorexia, bulging fontanelles, hyperirritability, vomiting

Vitamin A, acute (adult)

2 million IU

Headache, drowsiness, nausea, vomiting

Vitamin A, chronic (infant)

10,000 IU

Premature epiphyseal bone closing, long bone growth retardation

Vitamin A, chronic (adult)

50,000 IU

Anorexia, headache, bluffed vision, loss of hair, bleeding lips, cracking and peeling skin, muscular stiffness and pain, severe liver enlargement and damage, anemia, fetal abnormalities (pregnant women must be very careful), menstrual irregularities, extreme fatigue, liver damage, injury to brain and nervous system.

Vitamin B12 (Cobalamin)


No side effects from oral administration have been reported. (See thiamin)

Vitamin C, acute

10 gm

Nausea, diarrhea, flatulence

Vitamin C, chronic

3 gm

Increased urinary oxalate and uric acid levels in rare cases, impaired carotene utilization, chelation (binding of vitamin C with minerals) and resultant loss of minerals may occur, sudden discontinuation can cause rebound scurvy. Kidney and bladder stones, urinary tract irritation, increased tendency for blood to clot, breakdown of red blood cells in persons with certain common genetic disorders (such as glucose-6-phosphate dehydrogenase deficiency, common in persons of African origin), may induce B12 deficiency.

Vitamin D, acute

70,000 IU

Loss of appetite, nausea, vomiting, diarrhea, headache, excessive urination, excessive thirst

Vitamin D, chronic

10,000 IU

Weight loss, pallor, constipation, fever, hypocalcaemia. In infants, calcium deposits in kidneys and excessive calcium in blood; in adults, calcium deposits throughout the body (may be mistaken for cancer) (pregnant women must be careful), deafness, nausea, kidney stones, fragile bones, high blood pressure, high blood cholesterol, increased lead absorption.

Vitamin E

1,000 IU

The safe dose is probably over 2,000, but some people experience weakness, fatigue, exacerbation of hypertension, increased activity of anticoagulants at 1,000 IU, while some research shows that as little as 300 IU can slow down the immune system. Can destroy some Vitamin K made in the gut. A small amount of immune suppression is probably a reasonable trade off for vitamin E's much needed antioxidant activity.

Vitamin K


No known toxicity with natural (phylloquinone); synthetic (menadione), while relatively safe, when administered to infants may cause hemolytic and liver enlargement. Anemia in laboratory animals.


75 mg

Gastrointestinal irritation, vomiting, adverse changes in HDL/LDL cholesterol ratios, impaired immunity. Nausea, anemia, bleeding in stomach, premature birth and stillbirth, abdominal pain, fever. Can aggravate marginal copper deficiency. May produce atherosclerosis.

We try to ensure that the information on the site is accurate and complete, but you should not rely on it for medical purposes. Data is obtained from third party sources and may be subject to change. Users are encouraged to cross-check data. Consult with your medical practitioner before making any changes to your supplemental intake, and never change any prescribed supplements or medicine on the basis of information herein without first taking advice from a doctor or fully qualified dietary specialist. The creators of this site will not be responsible for any loss suffered or incurred as a result of any reliance placed on the site or its contents.