Are there side effects of taking CLA?

December 23, 2025 •

4 min read

According to research, taking CLA supplements may cause a range of side effects, from mild digestive discomfort to more serious metabolic issues, especially at high doses. This means it is crucial for consumers to understand the potential risks associated with taking CLA.

Quick Summary

This article explains the common and more serious side effects associated with conjugated linoleic acid (CLA) supplements, based on clinical research findings. It covers risks like digestive problems, metabolic issues, liver concerns, and potential interactions with other medications.

Key Points

Digestive Upset is Common: Mild but frequent side effects of CLA include stomach pain, nausea, diarrhea, and heartburn, especially when starting supplementation.
Metabolic Risks are a Concern: At higher doses, CLA has been linked to potential increases in insulin resistance, particularly in individuals with pre-existing metabolic issues like diabetes.
Liver Health Can Be Affected: Some animal and rare human studies suggest a risk of increased liver fat or damage, though other human trials have not confirmed this.
Impacts on Cholesterol: Supplemental CLA may negatively impact cholesterol profiles, specifically by potentially lowering 'good' HDL cholesterol, unlike the benefits associated with CLA from food.
Not Safe for All: Individuals with diabetes, bleeding disorders, and those who are pregnant or breastfeeding should avoid CLA supplements unless advised by a doctor.
Food vs. Supplement Differences: Natural CLA from food sources like grass-fed beef and dairy has a different composition and is generally considered safe, while synthetic supplements contain higher, altered doses with greater risks.

Conjugated linoleic acid (CLA) is a naturally occurring fatty acid found in the meat and dairy products of ruminant animals. However, the CLA used in most supplements is synthesized by chemically altering linoleic acid from vegetable oils, leading to different isomer ratios than those found in nature. While marketed for its potential weight loss benefits, it is important for consumers to be aware of the range of side effects that can accompany CLA supplementation.

Mild and Common Digestive Side Effects

One of the most frequently reported side effects of taking CLA is gastrointestinal distress, especially during the initial stages of supplementation. These issues are often mild but can be persistent for some users. They include:

Stomach upset and pain: Some individuals experience discomfort or cramps in the stomach area.
Diarrhea: Loose stools or diarrhea are common, particularly at higher doses.
Nausea and vomiting: Feelings of nausea or the urge to vomit can occur.
Heartburn: Acid indigestion or heartburn has also been reported by some users. These symptoms can often be mitigated by taking the supplement with food. However, if they persist, it may be a sign that the dosage is too high or that the supplement is not well-tolerated.

More Serious Metabolic and Liver Risks

Beyond mild digestive upset, several studies have raised concerns about more significant metabolic and liver-related risks, especially with high doses or long-term use of synthetic CLA supplements.

Potential for Worsened Insulin Resistance

Research suggests that supplemental CLA, particularly certain isomers like trans-10, cis-12, can worsen insulin resistance. This is a condition where the body's cells don't respond effectively to insulin, leading to higher blood sugar levels. This is a particular concern for individuals with or at risk for diabetes or metabolic syndrome, who should exercise caution and consult a healthcare provider before taking CLA.

Impact on Liver Health

There is conflicting evidence regarding CLA's effect on the liver. Some animal studies show that CLA can cause the accumulation of fat in the liver, a condition known as hepatic steatosis. In rare human cases, severe liver damage has been associated with CLA supplementation. However, other studies, including some on overweight women, have shown either no effect or even improved liver function with CLA supplementation. These discrepancies likely depend on the specific CLA isomers, dosage, and individual metabolic health.

Changes in Cholesterol Levels

While some research shows no effect on cholesterol, other studies have documented a decrease in high-density lipoprotein (HDL), or “good” cholesterol, in individuals taking CLA supplements. This is in contrast to the potential benefits of naturally occurring CLA from food sources. A drop in HDL cholesterol levels is a known risk factor for cardiovascular disease.

Comparison of CLA from Food vs. Supplements

It is important to differentiate between conjugated linoleic acid obtained from food sources and the synthetic versions found in most supplements. The composition and effects of each can vary significantly.


Feature	CLA from Food (e.g., grass-fed beef, dairy)	CLA from Supplements (synthesized)
Composition	Contains natural ratios of various CLA isomers.	Chemically altered from vegetable oils, often with different isomer ratios than natural CLA.
Dosage	Low, naturally occurring amounts (avg. 151-212 mg/day).	High, concentrated doses (typically 3-6 g/day).
Side Effects	Generally considered safe, part of a normal diet.	Potential for mild digestive issues; risk of more serious metabolic and liver concerns at high doses.
Health Impact	Associated with lower risk of certain diseases in observational studies.	Conflicting or modest results for weight loss; potential for negative metabolic effects.

Who Should Avoid CLA Supplements?

Certain populations should avoid or be extremely cautious with CLA supplementation due to heightened risk factors. This includes:

Individuals with diabetes or metabolic syndrome: The risk of worsening insulin resistance makes CLA potentially dangerous for this group.
People with bleeding disorders: CLA might slow blood clotting, increasing the risk of bruising or bleeding.
Those undergoing surgery: Due to the potential effect on blood clotting, it is recommended to stop taking CLA at least two weeks before any scheduled surgery.
Pregnant or breastfeeding women: There is insufficient reliable information to confirm the safety of large doses of CLA during these periods, so avoidance is recommended.

Conclusion

While some studies suggest minor weight loss benefits from CLA supplementation, these effects are often modest and inconsistent among individuals. Furthermore, the potential side effects, ranging from common digestive problems to more serious risks involving insulin sensitivity, liver health, and cholesterol levels, warrant careful consideration. The synthetic nature and high dosage of most supplements differ significantly from the CLA found naturally in food sources, and this is believed to contribute to the negative outcomes. It is highly recommended to consult a healthcare professional before starting CLA, especially if you have pre-existing health conditions or are taking other medications.

What are the symptoms of taking too much CLA?

Digestive issues like nausea, diarrhea, and stomach pain.
Fatigue and headaches.
Increased risk of insulin resistance.
Potential liver-related issues.

Frequently Asked Questions

Yes, some studies indicate that CLA supplements, especially at high doses, can lead to insulin resistance, which negatively impacts blood sugar control. This is a particular risk for people with diabetes or metabolic syndrome.

While some animal studies and rare human case reports have linked CLA to potential liver damage and increased liver fat, other studies in humans show no significant negative effect. The outcome may depend on the dose, specific CLA isomers, and the individual's metabolic status.

Yes, CLA from food sources like grass-fed dairy and beef is generally considered safe and is consumed in much lower doses. The higher doses and different isomer compositions of synthetic supplements are associated with a greater risk of side effects.

The most common digestive issues include nausea, diarrhea, stomach upset, and heartburn. These symptoms are more likely to occur at higher doses or when first starting supplementation.

Yes, CLA can interact with medications. For example, it might interfere with blood clotting, which is a concern for people on anticoagulant drugs. It may also affect insulin and other diabetes medications.

To potentially reduce mild digestive side effects, you can try taking your CLA supplement with a meal. If symptoms persist or are more serious, it is best to reduce the dosage or stop taking the supplement and consult a healthcare provider.

No, not everyone experiences side effects. Many individuals tolerate CLA well, especially at lower doses. However, the risk of side effects increases with higher dosages.