Can a Calcium Supplement Give You Diarrhea? Understanding the Gut Reaction

November 24, 2025 •

5 min read

According to a review of seven clinical trials, individuals taking calcium supplements reported higher rates of gastrointestinal issues, including diarrhea, than those on a placebo. This common side effect, while often mild, can raise concerns for many people who rely on supplements for bone health, prompting the question: can a calcium supplement give you diarrhea?.

Quick Summary

Calcium supplements can cause gastrointestinal side effects like diarrhea, especially at high doses or with certain formulations. The likelihood of experiencing loose stools depends on the type of calcium, dosage, and individual tolerance. Simple adjustments can often mitigate this digestive discomfort.

Key Points

High Doses Are a Culprit: Taking high doses of calcium (over 1,500mg daily) can overwhelm the body's absorption capacity, potentially causing diarrhea.
Formulation Matters: The type of calcium compound affects digestive tolerance; calcium carbonate is more commonly linked to constipation, while calcium citrate can sometimes cause loose stools.
Splitting the Dose Helps: To improve absorption and reduce GI side effects, split your daily calcium intake into smaller doses of 500mg or less taken throughout the day.
Take with Food: Consuming calcium supplements with meals can slow absorption and minimize irritation to the digestive tract.
Hydration is Key: Always drink plenty of water when taking supplements, as it helps regulate bowel movements and prevents dehydration.
Consider Other Supplements: Check if other supplements you're taking, such as magnesium, are contributing to your loose stools, as they can also have a laxative effect.
Consult a Professional: If symptoms persist or worsen, seek medical advice to rule out other issues and determine the best course of action.

Why Calcium Supplements Cause Digestive Distress

While essential for bone health, calcium supplements are known to cause gastrointestinal side effects in some individuals. Diarrhea is one of the possible reactions, though constipation is also very common. The cause of these issues lies primarily in how the body processes and absorbs the mineral, particularly at higher dosages.

One of the main reasons for digestive upset is the effect of high calcium concentrations on the intestines. Unabsorbed calcium can draw water into the colon, leading to osmotic diarrhea. Some evidence also suggests that calcium may alter gut motility in sensitive individuals. The type of calcium compound is a major factor, as different formulations have varying effects on the digestive system.

The Role of Calcium Formulations

The formulation of a calcium supplement significantly impacts its digestive tolerability. This is why some people experience loose stools, while others might deal with constipation when taking a different type of supplement.

Calcium Carbonate: This is one of the most common and inexpensive forms of calcium found in many over-the-counter supplements and antacids like Tums. It contains a higher percentage of elemental calcium but requires stomach acid for proper absorption. For many, this form is associated with constipation, but in some cases, it can cause other GI issues, including gas, bloating, and diarrhea.
Calcium Citrate: Often recommended for its higher tolerability, calcium citrate is less likely to cause constipation and is better absorbed with or without food. However, for a small subset of people, this form can have the opposite effect and cause loose stools or diarrhea.

Can a Calcium Supplement Give You Diarrhea? Prevention and Management

If you experience loose stools from a calcium supplement, it does not mean you must stop taking it altogether. Several strategies can help minimize or prevent the discomfort. Trying a different approach can often make a significant difference.

Switch Calcium Type: As mentioned, calcium carbonate tends to be more constipating, while calcium citrate is typically easier on the stomach but can cause loose stools in some. Experimenting with these or other forms like calcium lactate or phosphate may reveal a better-tolerated option.
Lower the Dose: Taking excessive amounts of calcium can overwhelm the intestines and trigger digestive issues. The NHS advises that high doses (over 1,500mg daily) can lead to stomach pain and diarrhea. Reduce your dose and see if symptoms improve.
Split Doses: The body absorbs smaller doses of calcium more efficiently. Instead of taking your entire dose at once, split it into smaller amounts throughout the day. For example, take 500mg in the morning and 500mg in the evening.
Take with Food: Taking supplements with a meal can slow absorption and reduce gastrointestinal side effects. This is particularly important for calcium carbonate, which relies on stomach acid for absorption.
Ensure Proper Hydration: Staying well-hydrated helps regulate bowel movements. Drinking plenty of water is essential when taking any supplement, including calcium.
Assess Other Supplements: Other supplements, such as magnesium, are known for their laxative effects. If you take a calcium-magnesium combination and experience loose stools, try isolating the supplements to see which one is the culprit. Sometimes, taking them separately or adjusting the dosage can solve the problem.

Comparison of Common Calcium Supplements


Feature	Calcium Carbonate	Calcium Citrate	Calcium Phosphate	Calcium Lactate
Elemental Calcium	High (~40%)	Lower (~21%)	Variable (~31-39%)	Lower (~13%)
Best Absorption	With food	Can be taken with or without food	Well absorbed, doesn't rely on stomach acid	Better absorbed in acidic environment
Cost	Generally inexpensive	Slightly more expensive	Moderate	Moderate
Common GI Side Effects	Constipation, gas, bloating	May cause loose stools in some individuals	Minimal gas or constipation	Less likely to cause digestive upset than carbonate

Conclusion

Yes, a calcium supplement can give you diarrhea, but it's not a universal side effect and can often be managed with simple adjustments. The likelihood and severity of digestive issues depend on factors like the type of calcium, the dosage, and your individual sensitivity. Switching to a different formulation like calcium citrate, splitting the daily dose, and taking it with food are effective strategies for many. If you continue to experience bothersome symptoms despite these changes, consult a healthcare provider to explore alternatives or rule out other underlying causes.

For more in-depth information, you can read about potential side effects from calcium supplementation reviewed by the National Institutes of Health.

What are the main mechanisms by which calcium can cause diarrhea?

Calcium supplements can cause diarrhea through several mechanisms. Unabsorbed calcium can increase the electrolyte content in the intestinal lumen, leading to osmotic diarrhea where water is drawn into the colon. It can also alter gut motility, especially in sensitive individuals.

Can switching from calcium carbonate to calcium citrate help with diarrhea?

Yes, for some people, switching from calcium carbonate to calcium citrate can help. Calcium carbonate is more commonly associated with constipation and general GI disturbances, while citrate is often better tolerated. However, in a smaller group of individuals, calcium citrate may lead to loose stools instead.

Is taking a high dose of calcium more likely to cause diarrhea?

Yes, taking high doses of calcium, especially more than 1,500mg per day, increases the likelihood of experiencing digestive side effects like stomach pain and diarrhea. The body can only absorb a certain amount of calcium at once, so large doses can overwhelm the system.

Should I stop taking my calcium supplement if it gives me loose stools?

Do not stop taking a supplement without consulting a healthcare provider. First, try strategies like splitting your dose, taking it with food, or switching to a different type of calcium. If symptoms persist, a doctor can help determine the best course of action.

What is the recommended way to take calcium to avoid digestive issues?

To minimize digestive side effects, take calcium in divided doses of 500mg or less throughout the day. Taking it with food can also help slow absorption and reduce gut irritation. Ensure you are also drinking plenty of water.

Can other ingredients in a calcium supplement cause digestive problems?

Yes, other ingredients or compounds in a supplement can contribute to GI issues. Magnesium, often combined with calcium, is a natural laxative and can cause loose stools. Additionally, artificial sweeteners found in some chewable forms can have a laxative effect.

When should I see a doctor about diarrhea from a calcium supplement?

While mild diarrhea is usually manageable at home, consult a doctor if you experience severe symptoms, such as persistent abdominal pain, blood in your stool, or signs of dehydration like excessive thirst or reduced urination. This is especially important if you are on other medications or have underlying health conditions.

Frequently Asked Questions

Calcium carbonate is more commonly associated with constipation rather than diarrhea, but it can cause other gastrointestinal issues like bloating, gas, and stomach pain in some individuals.

While generally better tolerated, for some people, calcium citrate can cause loose stools. This may be due to its effect on gut motility or an individual intolerance, but it is considered a less common side effect compared to the constipation associated with calcium carbonate.

Yes, combination supplements can sometimes cause diarrhea, as magnesium is a natural laxative and can counteract the constipating effect of calcium. If this happens, you may need to adjust the dose or take them separately.

To prevent diarrhea, take calcium supplements in smaller, divided doses of 500mg or less. Take calcium carbonate with a meal to aid absorption, and consider switching to a calcium citrate formula, which may be better tolerated.

Yes, what is sometimes perceived as an allergy can actually be an intolerance to calcium supplements, which can cause symptoms like cramping, nausea, and diarrhea. Trying an alternative form of calcium may resolve the issue.

Mild diarrhea from calcium supplements is usually not serious and can be managed with dosage and formulation adjustments. However, persistent or severe diarrhea could lead to dehydration and should be discussed with a healthcare provider.

Not all types of calcium supplements are equally likely to cause diarrhea. Side effects vary by individual and formulation, with some people reacting differently to various forms like carbonate versus citrate.