Does CLA Have Any Side Effects? What You Need to Know

November 15, 2025 •

2 min read

According to research, CLA (conjugated linoleic acid) is found naturally in dairy and meat from ruminant animals, but supplements can contain a different, synthetic form. While typically considered safe at recommended doses, many studies show that does CLA have any side effects when taken in higher, supplemental quantities.

Quick Summary

This article provides a comprehensive overview of the potential side effects associated with conjugated linoleic acid (CLA) supplementation, detailing common gastrointestinal issues and more serious risks like insulin resistance and liver concerns. It also clarifies differences between dietary CLA and synthetic supplement forms.

Key Points

Gastrointestinal Issues are Common: Mild side effects frequently include stomach upset, nausea, diarrhea, and indigestion, which may decrease with time. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}
Insulin Resistance is a Risk: High doses of synthetic CLA, particularly the t10,c12 isomer, can increase insulin resistance, making it unsuitable for people with diabetes or metabolic syndrome. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}
Fatty Liver Disease is a Concern: Accumulation of fat in the liver has been observed in both animal and some human studies, indicating a potential for liver damage with high CLA intake. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}
Negative Impact on Cholesterol: Some evidence shows that CLA supplements can lower 'good' HDL cholesterol, raising concerns for cardiovascular health. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}
Risk Varies by Source: CLA from natural food sources is not associated with the same risks as the higher doses of synthetic CLA found in supplements. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}
Interactions with Medication: CLA may interact with blood thinners and blood pressure medication, and should be avoided prior to surgery. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}
Specific Populations Should Avoid: Pregnant and breastfeeding women, along with those with bleeding disorders, should not take CLA supplements due to safety concerns and lack of research. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}

Understanding CLA and the Source of Side Effects

Conjugated Linoleic Acid, or CLA, is a naturally occurring fatty acid found in dairy products and meat from ruminant animals like cows and sheep. It is often marketed as a weight-loss supplement, but the CLA in these products is typically a synthetic version derived from vegetable oils, such as safflower oil. This synthetic form contains a different balance of isomers than the natural form. Most side effects are linked to supplemental use and tend to increase with higher doses. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}

Common Gastrointestinal Side Effects

Many users experience mild and temporary digestive issues when taking CLA supplements. These symptoms can often be mitigated by reducing the dose or taking the supplement with food. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}

More Serious Metabolic and Liver Risks

Higher doses of CLA supplements can pose more significant health concerns, particularly affecting metabolic function and the liver. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}

Comparative Overview: CLA from Food vs. Supplements

It is important to understand the differences between CLA from food and synthetic supplements. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}

Who Should Avoid CLA Supplements?

Certain individuals should be cautious or avoid CLA supplementation due to potential adverse effects. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}

Weighing the Risks Against Unproven Benefits

Synthetic CLA supplements carry notable risks, particularly at higher doses, while marketed benefits for weight loss are often modest and inconsistent. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}

Always consult a healthcare provider before starting supplementation. {Link: Consensus https://consensus.app/search/what-are-the-adverse-effects-of-conjugated-linolei/uRjE4TkWReKG4cia_hhFjg/}

Conclusion

While natural CLA in food is generally safe, synthetic CLA supplements, especially at higher doses, pose risks. Common side effects include digestive issues like nausea and diarrhea. More serious risks involve increased insulin resistance, potential fatty liver disease, and negative changes to HDL cholesterol. Individuals with diabetes, metabolic syndrome, bleeding disorders, or who are pregnant or breastfeeding should avoid CLA supplements. Given the often limited efficacy for weight loss, potential side effects should be carefully considered against the unproven benefits. Always consult a healthcare provider before starting supplementation.

Frequently Asked Questions

CLA in food comes from ruminant animals and is predominantly the cis-9, trans-11 isomer, consumed in small amounts. Supplement CLA is synthetic, derived from vegetable oils, contains a different ratio of isomers, and is taken in much higher, concentrated doses.

Yes, common side effects of CLA supplements include stomach upset, nausea, diarrhea, constipation, and heartburn, especially during the initial phase of supplementation.

Yes, people with diabetes or metabolic syndrome should avoid CLA supplements. Studies show that higher doses can increase insulin resistance and worsen blood sugar control.

Large supplemental doses of CLA have been linked in animal studies to fat accumulation in the liver. While research in humans is ongoing, some case reports suggest potential liver toxicity, so caution is advised.

While natural CLA might have positive effects, some research indicates that synthetic CLA supplements can lower 'good' HDL cholesterol levels, which is considered a negative effect for heart health.

No, there is insufficient reliable information on the safety of CLA supplements for pregnant and breastfeeding women, and they are generally advised to avoid them.

Yes, CLA can interact with medications that slow blood clotting (anticoagulants), increasing the risk of bruising and bleeding. It may also affect blood pressure, so caution is advised if you take blood pressure medication.