Does zinc cause constipation?

Constipation is not one of the side effects zinc supplements are known for. The trials keep finding gut trouble higher up, in the stomach. In a meta-analysis of 28 randomized trials in 5446 adults taking zinc for colds and other respiratory infections, nausea or stomach discomfort was 46% more common on zinc than on placebo (RR 1.46, 95% CI 1.03 to 2.06). Any non-serious side effect came to one extra person for every 7 treated. Constipation is not reported as a pooled outcome in that review or in the five others we read. Where it appears at all, it is a handful of single reports.

Unsettled. No trial or review we found measured constipation as an outcome of zinc. The answer rests on side effects counted in trials about colds, diarrhea and period pain, where constipation was never reported on its own. That makes a confident no hard to give. It also means nobody has found a yes.

What the trials found

Adults

The review of 28 trials above used mostly lozenges, and rated the evidence on non-serious side effects as moderate certainty. The 2024 Cochrane review of zinc for the common cold found zinc used as treatment probably raises non-serious side effects, RR 1.34 (95% CI 1.15 to 1.55), across 16 studies and 2084 people, on moderate-certainty evidence. Used to prevent colds, the estimate was RR 1.11 (95% CI 0.84 to 1.47), which does not reach significance. We could read only the abstract of that review, so we cannot say whether constipation was ever recorded in its tables.

In a meta-analysis of 6 randomized trials in 739 women taking zinc for period pain, side effects did not differ significantly from placebo. The odds ratio was 2.54 with a wide interval, 0.78 to 8.26, because there were few events. Only 11 women reported mild side effects such as stomach discomfort and nausea.

Children

Vomiting is the side effect that shows up in children. In 11 trials with 7043 children treated for diarrhea, zinc raised vomiting by 46% (RR 1.46, 95% CI 1.22 to 1.76, moderate certainty). The risk was comparable to placebo at 5 and 10 mg and higher at 20 mg. These children had diarrhea, so constipation was not an outcome anyone was looking for. The Cochrane review of preventive zinc in children aged 6 months to 12 years found more children with at least one episode of vomiting, RR 1.29 (95% CI 1.14 to 1.46), on high-quality evidence from five studies. The absolute rates per group are not in what we extracted from either review.

Dose

The clearest picture of dose comes from pooled patient data from 4 placebo-controlled trials of polaprezinc in people with zinc deficiency. Gut side effects ran at 0.0% on 75 mg, 2.1% on 150 mg and 14.9% on 300 mg, against 3.0% on placebo. Those were Japanese trials of one zinc compound, and the paper does not report constipation separately in its text.

Where constipation does turn up

In a randomized study of 40 healthy people given 150 mg of zinc a day for four weeks, 21 of the 37 who finished had nausea, stomach discomfort or headache. The trial's own table logs constipation twice, both times in one zinc acetate group. There was no placebo arm, so those two events cannot be compared with anything. Zinc acetate caused more unwanted effects than zinc gluconate (P = 0.001).

In a crossover trial of 25 people with rosacea taking 100 mg of zinc sulfate three times a day, the only side effect reported was mild stomach upset in 3 people, 12%. In a surveillance study of 358 people in India taking vitamin C and zinc tablets for 12 weeks, 2 people, 0.6%, reported constipation. That study had no comparison group, combined zinc with vitamin C and was supported by industry.

Zinc from food

Among 883 adults over 65 in Turkey, those with functional constipation ate less zinc than those without it. They also ate less energy, fluid, water, protein, fiber and several other minerals. That difference was unadjusted, and zinc intake tracks how much food and fiber people eat overall. The study cannot show that low zinc causes constipation, and it says nothing about supplements.

Who should be careful

Not for everyone. The gut side effects of zinc grow with the dose. NIH ODS lists nausea, dizziness, headaches, stomach distress, vomiting and loss of appetite as effects of too much zinc. It sets the upper limit at 40 mg a day for adults and 4 to 34 mg for infants, children and adolescents, depending on age. Doses of 50 mg or more over weeks can block copper absorption.

Copper is the less obvious cost. The Cochrane review of preventive zinc in children found a negative effect on copper status. If you take zinc with quinolone or tetracycline antibiotics or penicillamine, NIH ODS warns that they can interact. It also notes that some diuretics lower blood zinc by increasing its loss in urine. Both are worth raising with whoever prescribed the medicine.

What expert bodies say

NIH ODS lists the effects of too much zinc as nausea, dizziness, headaches, stomach distress, vomiting and loss of appetite. Constipation is not on that list. That is an agency summary without an analysis of its own. We did not find a guideline that addresses zinc and constipation directly.

If a zinc supplement upsets your stomach, the dose and the form are the first things worth discussing with whoever recommended it. If you are constipated while taking one, the evidence above gives no strong reason to blame the zinc.

How we searched

What would change this answer

• A meta-analysis that counts constipation separately in placebo-controlled zinc trials. The data probably exist in supplements and Cochrane tables, and nobody has pulled them out.
• A placebo-controlled trial at the doses people commonly take, with stool diaries. We found none.
• Bowel data from people on long courses of high-dose zinc, such as those treated for Wilson disease, where today there are only single counts.

Sources

1. ev-zco-01 · Meta-analysis or systematic review · rapid systematic review and meta-analysis of RCTs · n = 28 RCTs, 5446 participants
   Specifically, zinc increased the risk of nausea or gastrointestinal discomfort (RR 1.46, 95% CI 1.03 to 2.06),59 61 63 65–68 71–74 mouth irritation or soreness from sublingual lozenges (RR 1.55, 95% CI 1.05 to 2.29),59 61 63 65 66 72 73 and taste aversion from sublingual lozenges (RR 2.11, 95% CI 1.47 to 3.04),59 61 63 65 66 69 71 72 74 but not nasal irritation or pain from topical nasal sprays or gels (RR 1.22, 95% CI 0.72 to 2.05) (online supplemental appendix 4).
   
   Who: adults in randomized controlled trials of oral or intranasal zinc for acute viral respiratory tract infections
   Effect: nausea or GI discomfort RR 1.46 (95% CI 1.03 to 2.06); any non-serious AE RR 1.41 (1.17 to 1.69), NNH 7
   Certainty: moderate certainty for non-serious AEs (GRADE); mostly lozenges; constipation not pooled
   BMJ Open, 2021 · checked 2026-10-07 · we read the fulltext
2. ev-zco-02 · Meta-analysis or systematic review · Cochrane systematic review of RCTs · n = 2084 participants, 16 studies
   There is probably an increase in the risk of non-serious adverse events when zinc is used for cold treatment (RR 1.34, 95% CI 1.15 to 1.55; I2 = 44%; 2084 participants, 16 studies; moderate-certainty evidence); no treatment study provided information on serious adverse events.
   
   Who: children and adults in randomized placebo-controlled trials of zinc for preventing or treating the common cold
   Effect: non-serious adverse events with treatment RR 1.34 (95% CI 1.15 to 1.55), moderate certainty; prevention RR 1.11 (0.84 to 1.47)
   Certainty: adverse events listed as taste, smell, vomiting, cramps, diarrhea; constipation not named; full text not in PMC
   Cochrane Database Syst Rev, 2024 · checked 2026-10-07 · we read the abstract
3. ev-zco-03 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 7043
   The results suggest that patients in the zinc supplementation group had a higher risk of vomiting compared to the control/placebo group (RR = 1.46; 95% CI = 1.22, 1.76; 11 trials, 7043 participants, moderate certainty of evidence) (Figure 4).
   
   Who: children under 10 years with acute or persistent diarrhea in randomized trials of zinc vs placebo or no zinc
   Effect: vomiting RR 1.46 (95% CI 1.22 to 1.76), moderate certainty; risk comparable to placebo at 5 and 10 mg, higher at 20 mg
   Certainty: commissioned by WHO; children with diarrhea, so constipation not an expected outcome
   J Glob Health, 2024 · checked 2026-10-07 · we read the fulltext
4. ev-zco-04 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of RCTs · n = 205,401 (vomiting: five studies)
   Supplementation was associated with an increase in the number of participants with at least one vomiting episode (RR 1.29, 95% CI 1.14 to 1.46, five studies, high-quality evidence).
   
   Who: children aged six months to 12 years in randomized trials of preventive zinc supplementation
   Effect: at least one vomiting episode RR 1.29 (95% CI 1.14 to 1.46), high-quality evidence; negative effect on copper status
   Certainty: constipation not reported as an outcome
   Cochrane Database Syst Rev, 2014 · checked 2026-10-07 · we read the abstract
5. ev-zco-05 · Meta-analysis or systematic review · systematic review and dose-response meta-analysis of RCTs using individual patient data · n = 4 RCTs; 253 on polaprezinc, 198 on placebo
   ADRs related to gastrointestinal disorders were the most frequently observed and implied a dose–response relationship: 0.0% (0/16) for polaprezinc 75 mg, 2.1% (4/190) for polaprezinc 150 mg, 14.9% (7/47) for polaprezinc 300 mg, and 3.0% (6/198) for placebo.
   
   Who: patients with zinc deficiency in randomized placebo-controlled trials of polaprezinc 75, 150 or 300 mg
   Effect: GI adverse drug reactions 0.0% (75 mg), 2.1% (150 mg), 14.9% (300 mg) vs 3.0% placebo
   Certainty: polaprezinc is zinc bound to L-carnosine; Japanese trials; constipation not reported separately in the text
   Nutrients, 2020 · checked 2026-10-07 · we read the fulltext
6. ev-zco-06 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 739
   Only 11 participants reported mild side effects, such as gastrointestinal discomfort and nausea [12,13,23].
   
   Who: women with primary dysmenorrhea in randomized placebo-controlled trials of zinc supplementation
   Effect: adverse events OR 2.54 (95% CI 0.78 to 8.26), not significant; 11 participants with mild GI discomfort or nausea
   Certainty: small number of events, wide interval; constipation not reported
   Nutrients, 2024 · checked 2026-10-07 · we read the fulltext
7. ev-zco-07 · Randomized controlled trial(s) · randomized intervention study without placebo · n = 40 randomized, 37 analyzed
   At least one of the common side effects nausea, gastric discomfort, and headache occurred in 21/37 participants, thus a higher frequency than the usual 10%. Zinc acetate had more unwanted effects than zinc gluconate (P = 0.001, Table 2).
   
   Who: healthy persons randomized to four zinc acetate or zinc gluconate regimens, 150 mg/day for four weeks
   Effect: nausea, gastric discomfort or headache 21/37; obstipation 2 events, zinc acetate 150 mg once daily arm (Table 2); acetate worse than gluconate, P = 0.001
   Certainty: no placebo arm; constipation count from the trial table, not from the quoted sentence
   Sci Rep, 2022 · checked 2026-10-07 · we read the fulltext
8. ev-zco-08 · Randomized controlled trial(s) · randomized double-blind placebo-controlled crossover trial · n = 25
   No important side-effects were reported apart from mild gastric upset in three (12%) patients on zinc sulfate.
   
   Who: patients with rosacea given zinc sulfate 100 mg or placebo three times a day, crossover after 3 months
   Effect: mild gastric upset 3/25 (12%) on zinc sulfate; no other important side effects
   Certainty: small single-center trial
   Int J Dermatol, 2006 · checked 2026-10-07 · we read the abstract
9. ev-zco-09 · Observational data · multicentre prospective post-marketing surveillance, no control group · n = 358
   The majority of patients reported gastrointestinal disorders, i.e., two (0.6%) patients reported constipation and gastritis, respectively.
   
   Who: Indian patients with vitamin C and zinc deficiency taking ascorbic acid and zinc effervescent tablets
   Effect: constipation 2 (0.6%), diarrhea 4 (1.1%), vomiting 3 (0.8%); all mild
   Certainty: no comparator; zinc combined with vitamin C; industry-supported
   Rev Recent Clin Trials, 2025 · checked 2026-10-07 · we read the abstract
10. ev-zco-10 · Observational data · cross-sectional study · n = 883
    The FC group had significantly lower total energy, fluid, water, protein, carbohydrate, magnesium, zinc, phosphorus, potassium, soluble fiber, insoluble fiber, total fiber, and fiber (g)/1000 kcal intake than the non-FC group (p < 0.05).
    
    Who: adults aged over 65 from nursing homes and community health centers in Turkey, Rome IV criteria
    Effect: lower zinc intake in the constipation group (p < 0.05, unadjusted); fiber OR 0.98 (0.96 to 0.99) adjusted
    Certainty: unadjusted difference, zinc intake tracks total food and fiber intake; no causal inference
    J Am Nutr Assoc, 2023 · checked 2026-10-07 · we read the abstract
11. ev-zco-11 · Position of an expert body · agency fact sheet · n = —
    Getting excessive amounts of zinc can cause nausea, dizziness, headaches, gastric distress, vomiting, and loss of appetite. Doses of 50 mg of zinc or more over a period of weeks can inhibit copper absorption, reduce immune function, and lower high-density lipoprotein cholesterol levels; however, it is unlikely that a person would obtain this much zinc from food alone. The Tolerable Upper Intake Level for zinc is 40 mg for adults, and it ranges from 4 to 34 mg for infants, children, and adolescents, depending on age.
    
    Who: adults; children and adolescents have upper limits of 4 to 34 mg
    Effect: UL 40 mg/day for adults; 50 mg/day or more for weeks can impair copper absorption; constipation not listed
    Certainty: agency position without own analysis
    NIH Office of Dietary Supplements, Zinc Fact Sheet for Health Professionals · checked 2026-10-07 · we read the section
12. ev-zco-12 · Position of an expert body · agency fact sheet · n = —
    Zinc may interact with certain medications, such as quinolone antibiotics, tetracycline antibiotics, and penicillamine. In addition, some diuretics can decrease serum zinc concentrations by increasing zinc excretion in urine.
    
    Who: people taking quinolone or tetracycline antibiotics, penicillamine or diuretics
    Effect: no effect size; timing and status should be discussed with a clinician
    Certainty: agency position without own analysis
    NIH Office of Dietary Supplements, Zinc Fact Sheet for Health Professionals · checked 2026-10-07 · we read the section