Megavitamin therapy

March 22, 2017


Megavitamin therapy

Natural Standard Monograph, Copyright © 2013 (www.naturalstandard.com). Commercial distribution prohibited. This monograph is intended for informational purposes only, and should not be interpreted as specific medical advice. You should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.

Related Terms

  • Herbs, megadose therapy, megaminerals, minerals, orthomolecular medicine, orthomolecular programming, orthomolecular psychiatry, orthomolecular therapy, supplements, vitamins.

  • Note: Please see the Natural Standard Foods, Herbs & Supplements database for more information about individual vitamins.


  • Megavitamin therapy, also known as megadose vitamin therapy or orthomolecular therapy, involves taking vitamins in doses that exceed the recommended dietary allowance (RDA) in an effort to cure or prevent physical or mental disorders. The RDA refers to the recommended nutritional intake levels that have been established by the Food and Nutrition Board. Megavitamin therapy involves taking doses of vitamins that are up to 10 times greater than the RDA or up to five times greater with vitamin D. (Vitamin D is especially likely to have toxic effects when taken in high doses.)

  • Megavitamin therapy dates back to the early 1930s when psychiatrists began prescribing excessive doses of supplemental nutrients to treat severe mental problems. Vitamin B3 was the original substance used to treat conditions such as schizophrenia. Years later other vitamins, minerals, and hormones were added to treatments. In the 1950s, Biochemist Linus Pauling coined the term, "orthomolecular," which he defined as: "the preservation of good health and the treatment of disease by varying the concentration in the human body of substances that are normally present in the body."

  • Vitamins are nutrients that the body needs in order to grow, develop, and function normally. There are 13 essential vitamins that the body needs: vitamins A, C, D, E, K, and the B vitamins (thiamine, riboflavin, niacin, pantothenic acid, biotin, vitamin B-6, vitamin B-12, and folate). Each vitamin plays a different role in the body. For instance, vitamin C is necessary for the body to form collagen in bones, cartilage, muscle, and blood vessels. Because vitamins are found in food, a well-balanced diet typically provides all of the nutrients that the body needs.

  • Doctors often recommended multivitamins to individuals who eat poor diets or have difficulty absorbing nutrients. For example, multivitamins are usually recommended for people older than 60 years of age because as the body ages, it becomes more difficult to absorb certain vitamins. However, experts disagree whether multivitamins are necessary if a person eats a healthy and well-balanced diet.

  • Not everyone requires the same amount of each vitamin. The recommended daily dose varies depending on a person's age, gender, overall health and eating habits. For instance, when a woman becomes pregnant, her body requires 50% more iron to support the growing fetus.

  • There are two main types of vitamins: fat-soluble and water-soluble. Unlike water-soluble vitamins that need to be replaced regularly in the body, fat-soluble vitamins are stored in the liver and fatty tissues. Then, when these vitamins are needed, the body takes them out of storage to be used. Therefore, fat-soluble vitamins are generally eliminated much more slowly that water-soluble vitamins. Eating fats or oils that are not easily digested may cause deficiencies of fat-soluble vitamins. In general, the higher the percentage of saturated fatty acids in a fat, the more difficult the fat is to digest. Beef fat is one of the most difficult fats to digest. However, deficiencies of fat-soluble vitamins are uncommon in the United States.

  • Water-soluble vitamins are easily absorbed by the body. Unlike fat-soluble vitamins, bile acids are not needed to absorb them. The body does not store large amounts of water-soluble vitamins. Instead, the water-soluble vitamins that are not needed are removed by the kidneys and excreted in the urine. Therefore, these vitamins need to be consumed regularly. Water-soluble vitamins are less likely to cause toxicity than fat-soluble vitamins.

  • Because vitamins are vital to a person's health, vitamin deficiencies may cause serious health problems. For example, if a person does not consume enough iron in the diet, he/she may develop iron deficiency anemia (low levels of iron in the blood). Individuals who do not consume enough vitamin D may develop a condition called osteomalacia. This condition causes the bones to become soft. Vitamin K is another important vitamin. If a person does not consume enough vitamin K, he/she may have an increased risk of bleeding.

  • When vitamins are consumed in excess of the body's physiological needs, they may have drug-like effects and may also compromise the effectiveness of standard medical treatments. For instance, vitamin K may interfere with blood-thinning drugs (e.g. warfarin) and increase the risk of clotting. Therefore, megavitamin therapy should be use cautiously under the strict supervision of a healthcare professional.


  • Megavitamin therapy has been used to treat cancer, heart disease, schizophrenia, attention deficit hyperactivity disorder (ADHD), and the common cold. Research suggests that increased amounts of certain vitamins and minerals, including vitamins A, C, E, B6 (pyridoxine), and folic acid, may help prevent or delay the onset of some diseases. However, some megavitamin therapies, especially ones that involve vitamins A, D, E, K, and B6 (pyridoxine) may cause potentially serious adverse effects and are unsafe. Some vitamins or minerals, such as niacin, are beneficial at low levels, but toxic at high levels. Megavitamin therapy with other types of vitamins are not supported by conclusive scientific evidence.



Food and drink sources

Daily amount for adult men

Daily amount for adult women

Reported side effects of high oral doses

Biotin (vitamin H)

Biotin helps the body use nutrients. It is good for the nervous system, and it helps the body form red blood cells.

Eggs, fresh vegetables, kidney, liver, rolled oats.



No significant toxicity has been reported with biotin intake.

Folate and folic acid

Folate and folic acid help the body maintain and produce new cells. It also helps prevent iron deficiency anemia, as well as neural tube birth defects.

Asparagus, avocado, baked beans, banana, beef liver, black- eyed peas, bread, broccoli, cereal, chicken, cowpeas, bread, flour, fruits, cantaloupe, egg noodles, fish, fortified breakfast cereals, great northern beans, green beans, green leafy vegetables, legumes, lettuce, orange, orange juice, liver, papaya, pasta, peanuts, poultry, red meat, rice, spinach, tomatoes, turnip greens, vegetables, wheat germ, yeast.



Very high doses may cause significant central nervous system (CNS) side effects. Supplemental folic acid might increase seizures in people with seizure disorders, particularly in very high doses. However, the risks are low. Note: High levels of folic acid may mask the signs of B12 deficiency, especially in older adults.

Vitamin A (retinol)

Vitamin A is needed for vision. It also helps the body maintain healthy skin and mucus membranes. It is important for immunity, tissue repair, bone growth and the development of embryos. It also has antioxidant effects.

Apricots, beef, cantaloupe, carrots, cheese, chicken, dark leafy vegetables, kale, liver, mango, milk, oatmeal, papaya, peaches, peas, peppers, spinach, tomatoes, sweet potatoes, pumpkin, yellow squashes.



Excessive doses may cause nausea, vomiting, headache, blurred vision, dizziness, liver problems, birth defects, and clumsiness. It may also increase a person's risk of developing osteoporosis. Note: People who do not eat enough protein, drink high amounts of alcohol, or have liver problems or high cholesterol may have an increased risk of experiencing these side effects.

Vitamin B1 (thiamin)

Vitamin B1 helps the body convert carbohydrates (sugars) into energy. It is important for the nervous system.

Brewer's yeast, legumes, nuts, organ meats, pork, seeds, whole grain products.



Thiamin is generally considered safe and relatively nontoxic, even at high doses. Large doses may cause drowsiness or muscle relaxation.

Vitamin B2 (riboflavin)

Vitamin B2 is involved in vital metabolic processes in the body. It is necessary for normal cell function, growth, and energy production.

Beef, bread, broccoli, collard greens, cheese, dairy products, eggs, enriched or fortified grain products, liver, meats, milk, noodles, organ meats, pork chops, spinach, tuna, yogurt.



In general, the limited capacity of human adults to absorb oral riboflavin limits its potential for harm. Riboflavin intake many times higher than the RDA has not demonstrated toxicity. Nevertheless, the photosensitizing properties of riboflavin raise the possibility of some potential risks. Other possible reactions to very high doses include itching, numbness, burning/prickling sensations, and yellow discoloration of the urine.

Vitamin B3 (niacin)

Vitamin B3 helps the body process protein and fats. It also helps the body maintain a healthy nervous system and skin.

Animal protein, whole grain products.



Excessive doses of vitamin B3 may cause flushing (reddening of the skin) and upset stomach.

Vitamin B5 (pantothenic acid)

Vitamin B5 is a component of coenzyme A (CoA), a molecule that is necessary for many vital chemical reactions in cells. This vitamin is essential for the metabolism of carbohydrates, proteins, and fats, as well as for the production of hormones and cholesterol.

Animal products, legumes, whole grain cereals.



Moderate doses have been ingested without significant reported adverse effects. Large amounts of pantothenic acid taken by mouth may cause diarrhea. In theory, nausea and heartburn may occur.

Vitamin B6 (pyridoxine)

Vitamin B6 is needed for the production of the neurotransmitters serotonin and norepinephrine. It is also needed for the body to produce myelin, the fatty covering that insulates the nerves in the brain and spinal cord. It also helps the blood carry oxygen to the body tissues, helps the body break down copper and iron, and helps maintain normal blood sugar levels.

Avocado, banana, bran, bread, chicken, chickpeas, fish, flour products, fortified breakfast cereal, garbanzo beans, kidney, lima beans, liver, oatmeal, pasta, peanut butter, pork, potato, roast beef, soybeans, spinach, starchy vegetables, sunflower seeds, tomatoes, trout, tuna, walnuts, wheat bran.



Excessive doses of vitamin B6 may cause nerve damage in the arms and legs, which may cause tingling, numbness, pain, and/or difficulty walking.

Vitamin B12 (cobalamin, cyanocobalamin)

Vitamin B12 helps the body maintain healthy nerve cells and red blood cells. It is also needed to make DNA, the genetic material in all body cells.

Beef, chicken, clams, dairy products, egg, fortified breakfast cereal, haddock, liver, meat, milk, mollusks, pork, salmon, shellfish, trout, tuna, yogurt.



No significant toxicity has been reported with vitamin B12 intake.

Vitamin C (ascorbic acid)

Vitamin C is necessary for the body to form collagen in bones, cartilage, muscle, and blood vessels. It also aids in the absorption of iron. It also has antioxidant effects.

Broccoli, collard greens, grapefruit, guava, lemons, limes, oranges, peppers, potatoes, spinach, strawberries, tomatoes.



Excessive doses of vitamin C may cause upset stomach, kidney stones, severe diarrhea, and increased iron absorption. Rarely, flushing, faintness, dizziness, and fatigue have been noted. Large doses may cause hemolysis (red blood cell destruction) in patients with glucose 6-phosphate dehydrogenase deficiency. High doses of vitamin C should be avoided in people with conditions aggravated by acid loading, such as cirrhosis, gout, renal tubular acidosis, or paroxysmal nocturnal hemoglobinuria.

Vitamin D (cholecalciferol)

Vitamin D helps the body absorb calcium and phosphorous. It is important for healthy immune system function. It helps prevents rickets and osteomalacia. It may also help prevent bone fractures from osteoporosis.

Beef, cheese, cod liver oil, egg, fortified breakfast cereal, fortified dairy products, liver, mackerel, margarine, milk, salmon, sardines, tuna. Note: Vitamin D is also made in the body after exposure to sunlight.

5-15mcg or 200- 400 IU

5-15mcg or 200- 400 IU

Excessive doses of vitamin D may cause nausea, vomiting, decreased appetite and weight loss, constipation, confusion, irregular heartbeat, hypercalcemia, excessive bone loss, and deposits of calcium and phosphate in the soft tissues.

Vitamin E (tocopherol)

Vitamin E is important for healthy blood flow and it helps repair body tissues. It also acts as an antioxidant.

Almonds, broccoli, corn oil, green leafy vegetables, hazelnuts, kiwi, mango, margarine, nuts, peanut butter, peanuts, safflower oil, soybean oil, spinach, sunflower oil, sunflower seeds, vegetable oil, wheat germ.

15mg or 22.5 IU

15mg or 22.5 IU

Recent evidence suggests that regular use of high-dose vitamin E may increase the risk of death (from "all causes") by a small amount. These conclusions have been criticized by some experts because they are based on re-calculations (meta-analyses) of the results of prior smaller studies which were of mixed quality, with variable results, and often in patients with chronic illnesses. Nonetheless, this is the best available scientific evidence currently, and therefore, chronic use of vitamin E should be used cautiously, and high-dose vitamin E should be avoided. Acute overdose of vitamin E is very uncommon. Note: People who take blood thinners should talk to their doctors before taking vitamin E supplements.

Vitamin K (phylloquinone, K1)

Vitamin K is necessary for normal blood clotting and the formation of bones in humans.

Broccoli, Brussels sprouts, cabbage, canola oil, collards, green leafy vegetables, kale, mustard greens, parsley, soybean oil, spinach, Swiss chard, turnip greens.



No significant toxicity has been reported with vitamin K intake. Note: People with bleeding disorders or taking blood thinners should talk to their doctors before taking vitamin K supplements.


  • General: A qualified healthcare professional should be consulted before making decisions about therapies and/or health conditions. The recommended daily amount of vitamins varies depending on a person's age, gender, overall health, and eating habits. A doctor can help patients determine what doses may be safe and effective.

  • It is also important that people tell their doctors if they are taking any multivitamins or dietary supplements because they may interact with medical treatments.

  • Side effects: It is unlikely that a person would overdose on vitamins that he/she gets from foods. However, since megavitamin therapy involves taking high doses of vitamin supplements, there are many potential health concerns with this therapy. The human body has a limited capacity to use vitamins in its metabolic activities. When vitamins are consumed in excess of the body's physiological needs, they may have drug-like affects and may also compromise the effectiveness of standard medical treatments. Please see the chart above for more information about reported side effects of high doses of specific vitamins.

  • High doses of fat-soluble vitamins are especially dangerous because the body stores the extra vitamins it is unable to use. As a result, these vitamins, including vitamins A, D, E, and K, may build up to toxic levels in the body if they are consumed in excessive amounts.

  • High doses of vitamin B6 (pyridoxine) are also considered unsafe because they may cause serious side effects, including nerve damage in the arms and legs.

  • Interactions: Some vitamins may interact with a person's medications. For instance, vitamin K may interfere with blood-thinning drugs (e.g. warfarin) and increase the risk of clotting.

  • Interference with medical tests: Taking excessive doses of vitamin supplements may cause problems with some medical tests. For example, excessive doses of vitamin C supplements may interfere with a blood-glucose test, which is commonly used to diagnose diabetes. Therefore, patients should tell their doctors if they are taking any multivitamins or dietary supplements.

  • Additional information: Please see the Natural Standard Foods, Herbs & Supplements database for more information about individual vitamins.

Author Information

  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).


Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.

  1. BC Cancer Agency. Vitamin Therapy, Megadose/Orthomolecular Therapy. www.bccancer.bc.ca.

  2. Haslam RH. Is there a role for megavitamin therapy in the treatment of attention deficit hyperactivity disorder? Adv Neurol. 1992;58:303-10. View Abstract

  3. Hathcock J N. Vitamins and minerals: efficacy and safety. Am J Clinical Nutrition. 1997;66:427-437. View Abstract

  4. National Institutes of Health (NIH). www.nih.gov

  5. Natural Standard: The Authority on Integrative Medicine. www.naturalstandard.com

  6. Vaughan K, McConaghy N. Megavitamin and dietary treatment in schizophrenia: a randomised, controlled trial. Aust N Z J Psychiatry. 1999 Feb;33(1):84-8. View Abstract

Copyright © 2013 Natural Standard (www.naturalstandard.com)

The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.


March 22, 2017