What are the side effects of taking zinc?

November 15, 2025 •

4 min read

According to the National Institutes of Health, a tolerable upper intake level of 40 mg of zinc per day has been established for adults. Exceeding this limit, particularly through supplementation, can lead to a range of mild to serious side effects, raising important questions about the safety of taking zinc.

Quick Summary

Taking excessive zinc can lead to several acute and chronic side effects, including gastrointestinal distress, flu-like symptoms, and long-term copper deficiency. High doses may also negatively impact immune function and cholesterol levels.

Key Points

Gastrointestinal Distress: High doses of zinc can cause acute symptoms like nausea, vomiting, stomach cramps, and diarrhea, particularly when taken on an empty stomach.
Copper Deficiency: Prolonged high zinc intake (above 40 mg/day for adults) can interfere with copper absorption, leading to a deficiency that can cause anemia and neurological damage.
Suppressed Immunity: Contrary to its immune-boosting reputation in moderate amounts, excessive zinc can actually hinder immune function and increase susceptibility to infections.
Altered Cholesterol Levels: Chronic high-dose zinc has been shown to lower levels of HDL, or 'good' cholesterol, increasing the risk for heart disease.
Flu-like Symptoms: Some individuals experience headaches, fatigue, fever, and chills, a condition known as 'metal fume fever' when inhaling zinc, but also possible with high oral intake.
Drug Interactions: Zinc supplements can reduce the effectiveness of certain medications, such as quinolone and tetracycline antibiotics, and should be timed carefully.

Zinc is an essential trace mineral vital for numerous bodily functions, including immune response, wound healing, and DNA synthesis. While many people take zinc supplements for their purported health benefits, taking too much can have significant adverse effects. It is important to distinguish between mild, acute symptoms and more severe, long-term complications of high zinc intake.

Short-term side effects of taking zinc

Excessive zinc intake, often from high-dose supplements, can cause immediate gastrointestinal and systemic discomfort. These acute side effects are typically temporary and resolve once zinc intake is reduced or stopped.

Nausea and vomiting: One of the most common reactions to high-dose zinc, especially when taken on an empty stomach. Zinc lozenges used for colds have been particularly associated with this effect.
Stomach cramps and diarrhea: A direct result of gastrointestinal irritation caused by excessive zinc.
Loss of appetite: This can occur alongside other digestive issues, leading to a general feeling of malaise.
Flu-like symptoms: Some individuals may experience fever, chills, fatigue, and headache, particularly if exposed to zinc fumes in an industrial setting or from very high oral doses.
Metallic taste: A peculiar and unpleasant metallic taste in the mouth is a commonly reported side effect, especially with zinc lozenges.
Irritation: Certain topical applications, such as nasal sprays containing zinc, have been linked to irritation of the nose and mouth. In some rare cases, they have even been linked to permanent loss of smell.

Chronic and severe side effects of high zinc intake

Long-term use of zinc supplements in doses exceeding the recommended upper limit can lead to more serious, systemic health issues. These effects are often tied to the mineral's interaction with other essential nutrients in the body.

Copper deficiency: This is one of the most significant chronic side effects of excess zinc. High zinc levels interfere with the body's ability to absorb copper, as both minerals compete for the same transport proteins in the intestines. A prolonged copper deficiency can lead to severe anemia, neutropenia (a low white blood cell count), and neurological problems, such as numbness and weakness in the limbs.
Altered iron function: Excess zinc can also impact iron absorption, potentially leading to a form of anemia.
Suppressed immune function: Paradoxically, while moderate zinc intake supports the immune system, chronic high doses can suppress it. Excess zinc can inhibit the function of T-cells, a crucial component of the immune response, making the body more susceptible to infections.
Reduced HDL ('good') cholesterol: Several studies have shown that high doses of zinc over an extended period can decrease levels of high-density lipoprotein (HDL) cholesterol, which is a risk factor for heart disease.

Comparison of acute vs. chronic zinc side effects


Symptom	Acute Effects (High single dose)	Chronic Effects (High long-term dose)
Gastrointestinal	Nausea, vomiting, diarrhea, stomach pain	Persistent digestive upset, reduced appetite
Neurological	Headache, fatigue, dizziness	Numbness, weakness in limbs, nerve damage from copper deficiency
Mineral balance	Mild, temporary interference	Severe copper and iron deficiency
Immune system	Flu-like symptoms (fever, chills)	Suppressed immune response, increased infections
Cholesterol	No immediate effect	Decreased 'good' HDL cholesterol

How to avoid side effects

Preventing the side effects of zinc involves responsible supplementation and being aware of dietary intake. The Tolerable Upper Intake Level (UL) for adults is set at 40 mg per day from all sources combined, including food, supplements, and fortified products.

Consider your sources

While zinc toxicity from food sources is very rare, supplements can easily push intake over safe levels. For example, a single serving of oysters contains a significant amount of zinc, but zinc poisoning from food alone is not documented. Therefore, it is important to be mindful of supplement dosages and to obtain the majority of zinc from a balanced diet of foods like meat, poultry, seafood, legumes, and nuts.

Mind your timing

Taking zinc supplements with food can significantly reduce the risk of gastrointestinal side effects like nausea. Furthermore, if you take certain antibiotics (like tetracycline or quinolone), it is crucial to take your zinc supplement at least 2 hours before or 4 to 6 hours after your medication, as zinc can interfere with its absorption.

Talk to a healthcare professional

Before starting any new supplement, especially one with a high dose of zinc, consult with a doctor or registered dietitian. They can assess your individual needs and potential risks, particularly if you have pre-existing conditions or are taking other medications.

Conclusion

While zinc is a crucial mineral for overall health, exceeding the recommended daily limits can lead to a variety of adverse side effects. Acute symptoms, such as nausea and stomach upset, are common with high doses, while long-term overuse can lead to serious issues like copper deficiency, suppressed immune function, and low 'good' cholesterol. By sticking to recommended dosages, considering dietary intake, and consulting a healthcare professional, individuals can reap the benefits of zinc while minimizing the risks associated with excessive consumption.

Frequently Asked Questions

Zinc toxicity from food sources is extremely rare, as it is difficult to consume amounts high enough to cause an overdose from naturally occurring zinc. Toxicity is almost always associated with high-dose supplementation.

For most healthy adults (age 19 and older), the Tolerable Upper Intake Level (UL) for zinc from all sources is 40 milligrams per day. Consuming higher amounts is not recommended unless under medical supervision.

Taking zinc supplements with food can help mitigate gastrointestinal issues such as nausea, vomiting, and stomach cramps. This is particularly useful for sensitive individuals or those taking higher doses.

Symptoms of copper deficiency caused by high zinc intake can include anemia that does not respond to iron, neutropenia (low white blood cells), and neurological issues such as numbness and weakness in the arms and legs.

Yes, zinc can interfere with the absorption of certain antibiotics, including tetracyclines and quinolones. It's recommended to take zinc at least 2 hours before or 4-6 hours after these medications.

Topical zinc products, such as certain nasal gels and sprays, have been associated with a permanent loss of the sense of smell in some cases. This is why intranasal zinc is not recommended.

Individuals who take high-dose supplements, people with pre-existing health conditions, and those with a history of copper deficiency are at a higher risk. Always consult a healthcare provider before beginning supplementation.