Selenium Supplement (Oral Route)

Selenium is a naturally occurring metal found in some foods, which is necessary to the healthy function of the thyroid and immune system.


Selenium is a natural mineral found in a variety of different foods, including whole grains, some nuts, and seafood. Selenium is not naturally occurring in the body, but is necessary for patient health, and is necessary for the proper healthy function of both the thyroid and the immune system.

Selenium is only proven as a treatment for selenium deficiency. This fact, however, has not stopped some people from trying to expand the drug’s usefulness. Selenium is sometimes used as an alternative treatment for Hashimoto’s thyroiditis (an autoimmune disorder of the thyroid) and high cholesterol. Selenium is sometimes thought to reduce the risk of cancer.

Most patients will not need to take a selenium supplement. Patients who eat diets poor in selenium or who suffer from disease such as HIV or Crohn’s Disease, which impair nutrient absorption, are going to have the biggest need for selenium supplements.

Conditions Treated

  • Selenium deficiency
  • Hashimoto’s thyroiditis (alternative)
  • High cholesterol (alternative)
  • Cancer risk (unproven)

Type of Medicine

  • Mineral

Side Effects

Selenium on its own, as a staple in most human diets and a necessary mineral in trace amounts, has no known side effects on the human body. However, long-term over supplementation can have adverse effects on the human body.

Symptoms of long-term over supplementation can include:

  • Nausea
  • Vomiting
  • Lack of energy
  • Rogue sensations of extreme tiredness
  • Feelings of irritability
  • Hair loss
  • Rash
  • Brittle fingernails
  • Pain in the fingernails
  • White streaks in the patient’s fingernails

Additionally, long-term over supplementation with selenium may increase a patient’s risk of developing diabetes.

Despite its classification as a supplement, overdose on selenium is more than possible. Patients who fear they may have taken too much selenium should call poison control at 1 800 222 1222.

Symptoms of selenium overdose can include any of the following:

  • Diarrhea
  • Excessive sweating
  • Foul smelling breath, particularly a garlic-like smell
  • Hair loss
  • Irritability
  • Itchy sensations
  • Tremors
  • Feeling lightheaded
  • Tenderness in the muscles
  • Flushing
  • Metallic tastes in the mouth
  • Bad breath
  • Strong and foul body odor
  • Easy bruising
  • Easy bleeding
  • Nausea and vomiting
  • Unusual tiredness
  • Unusual weakness

Patients who begin to experience any of these symptoms while taking selenium should contact their doctor immediately and seek emergency medical attention.

This is not necessarily a complete list of side effects. Patients who begin to experience new or worsening symptoms after beginning to take selenium should stop taking selenium immediately and contact their doctor. Patients can report new side effects to the FDA at 1 800 FDA 1088 or on the web at


Selenium comes in pill or capsule form, depending on the company selling the selenium. Selenium supplements can sometimes be fortified with other supplements, vitamins, or minerals. Patients who only want to take selenium should make sure that the selenium pills or capsules they have are unfortified and contain no other supplements. Dosage requirements can vary considerably with age, weight, body composition, and diet. Patients should consult with their doctor to determine the optimal dose of selenium for them.

A patient’s need for selenium often increases with age.

Patients who have forgotten to take a dose of selenium should take the missed dose as soon as they remember. However, if it is nearly time for them to take their next dose, they should simply wait and take their next dose when it comes time to do so. Patients should never take a double dose in an attempt to retroactively make up for a mixed dose.


Selenium can interact negatively with the drug dimercaprol. Dimercaprol can bind to certain metals, including iron and selenium, to form a combination which can be toxic to the kidneys. Patients who are taking dimercaprol (a drug used to treat poisoning resulting from gold, arsenic, or mercury) should never supplement with selenium and may need to pursue a selenium free diet. Patients who need to take selenium and dimercaprol concurrently should consult with their doctor prior to deciding to supplement with selenium. Patients may need to consider alternative treatment options.

Selenium can interact negatively with antibiotics in the fluoroquinolone family. The absorption of fluoroquinolone antibiotics is impeded by a variety of different minerals and vitamins, including selenium. As a result, patients should never take a selenium supplement concurrently with a fluoroquinolone antibiotic. Patients may need to delay their dose of selenium up to 6 hours after taking a fluoroquinolone antibiotic. Patients taking a fluoroquinolone antibiotic should consult with their doctor prior to deciding to supplement with selenium.

Selenium can interact with a handful of other drugs.

The following drugs are known to interact negatively with selenium:

  • Alendronate
  • Deferiprone
  • Eltrombopag
  • Etidronate
  • Ibandronate
  • Nalidixic acid
  • Penicillamine
  • Risedronate
  • Sodium polystyrene sulfonate
  • Tiludronate
  • Trientine

Selenium can interact negatively with many treatments for Paget’s disease. Many treatments for Paget’s disease have their absorption hampered by different minerals and vitamins, including selenium. Patients should never take selenium concurrently with some treatments for Paget’s disease. Patients receiving treatment for Paget’s disease should consult with their doctor prior to deciding to supplement with selenium.

This is not necessarily a complete list of possible interactions. Patients should rely on their doctor to identify any possible interactions between selenium and any other drugs, medications, or supplements they are taking. Additionally, patients should disclose a complete list of all the drugs, medications, and supplements they are taking to their doctor.


Selenium is considered a class C drug in terms of pregnancy. This means that there is not enough data available to determine whether or not selenium has been shown to be safe for human fetuses. Patients who are pregnant should consult with their doctor before taking selenium. Dosage adjustments may be required. Additionally, the safety of breastfeeding while taking selenium has not been established. Patients who are breastfeeding should consult with their doctor prior to deciding to take selenium. Patients who are breastfeeding may also be required to adjust their dose of selenium to ensure the health of the breastfeeding child.

Selenium is toxic in large quantities. Patients who exceed the maximum daily intake of between 400 and 800 micrograms per day may experience selenosis. Symptoms of selenosis can include nausea, diarrhea, vomiting, and fatigue. Patients should be careful to take only the dose recommended to them by their doctor and to avoid exceeding the maximum daily dose of selenium in any given 24 hour period. Long-term use of selenium in doses which exceed the max daily limit can cause serious medical problems down the line, and may even cause death.

Patients who suffer from kidney disease should exercise extreme caution when considering taking selenium. Selenium is excreted through the kidneys, and any decrease in clearance may result in increased concentrations of selenium in the bloodstream or in the patient’s plasma. Patients with any renal impairment should consult with their doctor prior to deciding to take selenium.

Some patients have reported serious allergic reactions to selenium. Patients who are allergic to selenium should not take a selenium supplement. Patients should stop taking selenium immediately and contact their doctor immediately if they begin to experience signs of an allergic reaction, including hives, rash, swelling of the neck and throat, and even anaphylaxis. Depending on the strength of the reaction, emergency medical attention may be required.

Patients who are on dialysis may see their selenium supplementation affected by their dialysis treatment. Patients who are on dialysis and are also selenium deficient should consult with their doctor to determine the proper dosing schedule for the selenium supplement or an alternative treatment for their condition.

Patients with underactive thyroids may be adversely affected by selenium supplementation. Patients with an underactive thyroid should consult with their doctor before deciding to take selenium.

Skin cancer may also complicate selenium supplementation. Patients with skin cancer should consult with their doctor before deciding to take the selenium supplement.

Patients who are candidates for surgery may need to stop taking selenium. Heightened levels of selenium may cause unnecessary complications during surgery, making it simpler just to stop taking additional selenium. Patients who are considering surgery should consult with their doctor to determine whether or not it will be safe to supplement with selenium while preparing for surgery. Patients may need to stop taking selenium as far out as two weeks before their surgery.


Selenium supplements should be stored at room temperature, away from moisture and direct sunlight.


Selenium is proven to cure one ailment: selenium deficiency, which is an unpleasant condition in of itself. There is some indication that it can be used as a preventative measure against some cancers, especially skin cancer. Additionally, there is some evidence that selenium can help treat other conditions, such as high cholesterol or Hashimoto’s thyroiditis.

Selenium overdose and over supplementation can be serious, though, which can cause a number of unpleasant and painful symptoms and may even prove lethal. Patients who want to use selenium for uses that are unproven should seek the advice of their doctor to ensure they won’t just end up doing more long-term damage to themselves.

Despite being categorized as a supplement, selenium can be dangerous and demands respect. With proper medical advice and a healthy respect for the supplement, though, patients should be able to utilize selenium effectively to treat their conditions.


Last Reviewed:
February 01, 2018
Last Updated:
January 27, 2018