Selenium Safety & Side Effects
Our assessment
Based on FDA data, selenium supplements have a well-documented safety profile, but the margin between adequate intake and toxicity is narrow. The most critical finding is that excessive selenium intake—whether from supplements or high-selenium foods like Brazil nuts (68–91 mcg per nut)—can lead to serious adverse effects FDA FAERS ↗. The data does not provide a total count of adverse event reports for selenium, so this information is not available.
Safety profile
Based on FDA data, specific side effects from getting too much selenium include: garlic breath, metallic taste in the mouth, hair loss, brittle nails or nail loss, skin rash, nausea, diarrhea, extreme tiredness, irritability, and nervous system problems FDA FAERS ↗. The data does not provide individual report counts for each of these side effects.
Who should be cautious
Individuals taking cisplatin, a chemotherapy drug used to treat cancer, should be particularly cautious as it can lower selenium levels, though the effect this has on the body is not clear FDA FAERS ↗. The data does not specify a maximum safe dose threshold or provide information on other specific populations who should avoid selenium.
Our recommendation
Start with a low dose and avoid consuming large amounts of Brazil nuts alongside selenium supplements. The data does not provide an RDA or upper limit for selenium, so consult a healthcare provider for personalized guidance FDA FAERS ↗. If you experience garlic breath, metallic taste, hair loss, or brittle nails, discontinue use and consult your doctor.
AI-assisted analysis. Data sourced from NIH ODS and FDA.
Safety Overview
Yes, if you get too much selenium over time. Brazil nuts, for example, contain very high amounts of selenium (68–91 mcg per nut) and can cause you to go over the upper limit if you eat too many. Getting excessive amounts of selenium from dietary supplements can also be harmful. Getting too much selenium can cause: Garlic breath Metallic taste in the mouth Hair loss Brittle nails or nail loss Skin rash Nausea Diarrhea Extreme tiredness Irritability Nervous system problems Consuming very high amounts of selenium can cause severe stomach and nervous system problems, difficulty breathing, tremors , lightheadedness, flushing, muscle tenderness, kidney or heart failure , and heart attacks . In rare cases, it can cause death. The daily upper limits for selenium include intakes from all sources—food, beverages, and supplements—and are listed below. These upper limits do not apply if you are taking selenium under the care of a doctor. Some experts recommend daily upper limits for selenium that are lower than these amounts. For example, in 2023 the European Food Safety Authority set a daily upper limit for selenium of 255 mcg for all adults, with lower amounts ranging from 70 to 230 mcg for children and teens, depending on age.
Drug Interactions
Yes, selenium may interact with certain medications, and some medications may interact with selenium. For example, cisplatin, a chemotherapy drug that is used to treat cancer, can lower selenium levels, but the effect this has on the body is not clear. Tell your doctor, pharmacist , and other health care providers about any dietary supplements and prescription or over-the-counter medicines you take. They can tell you if the dietary supplements might interact with your medicines or if the medicines might interfere with how your body absorbs , uses, or breaks down nutrients.