Quick answer

NIH lists nausea, dizziness, headaches, stomach upset, vomiting and loss of appetite among the effects of too much zinc, and MedlinePlus says large amounts may cause diarrhea, cramps and vomiting within 3 to 10 hours. A Cochrane review found more non-serious adverse events with zinc used for colds.^1,2,3

Key facts

NIH says excessive zinc can cause nausea, dizziness, headaches, gastric distress, vomiting and loss of appetite.^1,4
MedlinePlus says stomach symptoms from large zinc supplements most often appear within 3 to 10 hours and go away shortly after stopping.²
A Cochrane review of 34 trials found non-serious adverse events probably more common in trials where zinc was started after a cold began, with a risk ratio of 1.34 (1.15 to 1.55).³
NIH sets the adult upper limit at 40 mg a day, and says high doses can leave a metallic taste.^1,5
Doses of 50 mg or more over weeks can inhibit copper absorption, which is the basis of the upper limit.¹

What NIH says about zinc and nausea

NIH's consumer sheet answers directly: yes, too much zinc can be harmful, and the signs include nausea, dizziness, headaches, upset stomach, vomiting and loss of appetite. The health professional sheet gives the same list and adds that it is unlikely a person would get this much zinc from food alone.^1,4

Too much zinc can cause nausea, vomiting, loss of appetite, stomach cramps, diarrhea and headaches. Dizziness has also been reported.^1,4,5

High intakes can leave a metallic taste in the mouth.⁵

Food rarely supplies as much as 50 mg of zinc a day, so zinc from food alone is unlikely to cause too much.¹

How soon do stomach symptoms from zinc appear, and at what amount?

MedlinePlus says zinc supplements taken in large amounts may cause diarrhea, abdominal cramps and vomiting, most often within 3 to 10 hours of swallowing, and the symptoms go away within a short period after stopping.²

The sources do not give one amount at which nausea begins. NIH's adult upper limit of 40 mg a day covers all sources and is set from copper, not from stomach upset, so a smaller amount can still upset an individual stomach.¹

What did a Cochrane review find about adverse events?

A Cochrane review of 34 trials with 8,526 people tested zinc against placebo for colds. It counted unpleasant taste, loss of smell, vomiting, stomach cramps and diarrhea among the adverse events potentially due to zinc. Non-serious adverse events were probably more common in the trials where zinc was started after a cold began, with a risk ratio of 1.34 (1.15 to 1.55), on moderate-certainty evidence. In the trials where zinc was taken ahead of colds, it was uncertain whether adverse events differed.³

In the review, zinc gluconate was given at 45 to 276 mg a day, above the 40 mg adult upper limit, which is one reason the findings cannot be carried over to a daily low-dose supplement.^1,3

Can too much zinc cause anemia or low copper?

NIH says doses of 50 mg or more over weeks can inhibit copper absorption and lower copper status. Low copper from zinc has been reported with denture cream used far beyond the label, with numbness, weakness and, in a few reports, anemia.^1,4

Taking 50 mg of zinc a day or more for weeks can block copper absorption and lower copper status, reduce immune function and lower HDL cholesterol.^1,4

Using far more zinc-containing denture cream than directed, at least a 70 g tube a week for several years, has led to low copper with numbness, weakness and loss of coordination.^1,4

Does zinc cause constipation, acne or hair loss?

The sources checked do not report constipation, acne or hair loss from extra zinc, which is not a finding either way. NIH links hair loss, or alopecia, to too little zinc in children, and a dermatology review calls alopecia a well-known sign of established zinc deficiency.^1,6

Who should ask a doctor about zinc and nausea

Anyone who has nausea, vomiting or stomach cramps after starting a zinc supplement, who should ask their doctor or pharmacist whether the amount is right.^1,2
Anyone taking more than 40 mg of zinc a day from all sources, or who also uses zinc lozenges, nasal products or denture cream.¹
Anyone on a quinolone or tetracycline antibiotic, penicillamine or a thiazide diuretic.¹

Questions people ask

Does zinc cause stomach upset?

NIH lists upset stomach, nausea and vomiting among the signs of too much zinc, and MedlinePlus says stomach symptoms from large amounts often appear within 3 to 10 hours. Ask your doctor or pharmacist.^2,4

Does zinc cause diarrhea?

MedlinePlus says large amounts of zinc supplements may cause diarrhea, abdominal cramps and vomiting. The Cochrane review counted diarrhea among its adverse events.^2,3

Does zinc cause headaches?

NIH lists headaches among the effects of excessive zinc, with nausea, dizziness and vomiting. Ask your doctor if they follow a supplement.^1,4

Does zinc cause anemia?

NIH says 50 mg or more a day over weeks can inhibit copper absorption, and zinc-containing denture cream used far beyond the label has led to low copper with anemia in a few reports.¹

Does zinc cause constipation, acne or hair loss?

The sources checked do not report these from extra zinc, which is not a finding either way. NIH ties hair loss to too little zinc. Ask your doctor or pharmacist.¹

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Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.