Complement Essential Review 2026: Worth the Price?

Serious risks

• The Food and Nutrition Board set no upper limit for B12 because its potential for toxicity is low.

Avoid or ask a doctor first if

• People who regularly take certain medications are told to talk with their health care providers about their B12 status.

Medication interactions

• B12 supplements may interact with some medications. Gastric acid inhibitors and metformin may affect B12 levels.
• Several types of medications might adversely affect B12 levels.

Possible side effects

• High blood calcium from vitamin D toxicity can lead to nausea, vomiting, muscle weakness, and other symptoms.

Serious risks

• Toxicity can cause high blood and urine calcium. In extreme cases it may lead to kidney failure, soft tissue calcification, heart rhythm problems, and death.
• Toxicity is almost always caused by taking too much vitamin D through supplements.

Avoid or ask a doctor first if

• The source says people on regular medications should talk with their health care providers about vitamin D intake and status.

Medication interactions

• Vitamin D supplements may interact with orlistat, statins, steroids, and thiazide diuretics.
• Taking calcium supplements with vitamin D supplements may raise the risk of certain adverse effects.

Possible side effects

• Commonly reported side effects of omega-3 supplements are usually mild and include unpleasant taste, bad breath, heartburn, nausea, stomach discomfort, diarrhea, headache, and odoriferous sweat.

Serious risks

• Two large trials found 4 g/day of omega-3 supplements for several years slightly increased atrial fibrillation risk in people with CVD or at high risk of CVD.
• The IOM noted that 900 mg/day EPA plus 600 mg/day DHA or more for several weeks might reduce immune function.
• Doses of 2–15 g/day EPA and/or DHA might increase bleeding time.

Medication interactions

• Omega-3 supplements such as fish oil have the potential to interact with medications.

Possible side effects

• High iodine intakes can cause goiter, elevated TSH levels, and hypothyroidism, some of the same symptoms as iodine deficiency.

Serious risks

• Iodine-induced hyperthyroidism can result from high iodine intakes, including when iodine is given to treat iodine deficiency.
• Studies have shown that excessive iodine intakes cause thyroiditis and thyroid papillary cancer.
• Acute iodine poisoning is rare and is usually caused by doses of many grams. Symptoms include burning of the mouth, throat, and stomach, fever, abdominal pain, nausea, vomiting, diarrhea, weak pulse, and coma.
• Long-term intakes above the UL increase the risk of adverse health effects.

Avoid or ask a doctor first if

• People with autoimmune thyroid disease or iodine deficiency may have adverse effects at iodine intakes considered safe for the general population.
• The ULs do not apply to people receiving iodine for medical treatment, who should be under a physician's care.

Medication interactions

• Iodine supplements have the potential to interact with several types of medications. People taking these medications on a regular basis should discuss their iodine intakes with their health care providers.

Possible side effects

• High doses from supplements or medications can cause diarrhea, nausea, and abdominal cramping.
• Magnesium carbonate, chloride, gluconate, and oxide are the forms most commonly reported to cause diarrhea.

Serious risks

• Very high doses can lead to magnesium toxicity, with low blood pressure, vomiting, difficulty breathing, irregular heartbeat, cardiac arrest and other signs.
• A few cases of fatal hypermagnesemia have been reported.
• Very large doses of magnesium-containing laxatives and antacids have been associated with magnesium toxicity.
• The risk of toxicity increases with impaired kidney function or kidney failure.

Avoid or ask a doctor first if

• People with impaired kidney function or kidney failure face higher risk of magnesium toxicity.
• People taking medications regularly should discuss their magnesium intake with their health care providers.

Medication interactions

• Magnesium may interact with oral bisphosphonates, tetracyclines, and quinolone antibiotics.
• Some medications, including diuretics and proton pump inhibitors, can affect magnesium status.

Possible side effects

• Early signs of too much selenium are a garlic odor on the breath and a metallic taste in the mouth.
• Hair loss and nail brittleness or loss are the most common clinical signs of chronically high selenium intake.
• Other signs of chronically high intake include skin rash, nausea, diarrhea, fatigue, irritability, and nervous system abnormalities.

Serious risks

• Acute selenium toxicity can cause severe gastrointestinal and neurological symptoms, respiratory distress syndrome, heart attack, kidney failure, cardiac failure, and, in rare cases, death.
• Acute toxicity has resulted from misformulated over-the-counter products containing very large amounts of selenium. In 2008, 201 people had severe adverse reactions to a liquid supplement with 200 times the labeled amount.
• Brazil nuts contain very high amounts of selenium and could cause selenium toxicity if eaten regularly.

Avoid or ask a doctor first if

• The upper limits do not apply to people taking selenium under a physician's care.
• People who take medications regularly should discuss their selenium status with their health care providers.

Medication interactions

• Selenium supplements may interact with medications, and some medications, such as cisplatin, can affect selenium levels in the body.

Possible side effects

• High zinc intakes can cause nausea, dizziness, headaches, gastric distress, vomiting, and loss of appetite.

Serious risks

• Doses of 50 mg or more taken for weeks can interfere with copper absorption, reduce immune function, and lower HDL cholesterol.
• Very high supplemental doses (142 mg/day) might interfere with magnesium absorption and disrupt magnesium balance.
• According to a few reports, overuse of zinc-containing denture adhesive creams can lead to neurological symptoms and anemia.

Avoid or ask a doctor first if

• The upper limits don't apply to people receiving zinc for medical treatment, who should be under a physician's care.
• Zinc-free denture adhesive formulations are available to prevent the effects linked to zinc-containing creams.

Medication interactions

• Zinc may interact with quinolone antibiotics, tetracycline antibiotics, and penicillamine.
• Some diuretics can lower serum zinc by increasing zinc excretion in urine.
• People taking medications regularly should discuss their zinc status with their health care providers.