What Are the Disadvantages of Glucosamine and Chondroitin?

November 21, 2025 •

3 min read

According to a 2017 U.S. survey, chondroitin (with or without glucosamine) was the dietary supplement most commonly used by people age 35 and older with an osteoarthritis diagnosis. However, despite their popularity, it is important to understand the potential disadvantages of glucosamine and chondroitin, which range from common digestive issues to serious drug interactions.

Quick Summary

Potential risks of glucosamine and chondroitin include gastrointestinal side effects, allergic reactions, and interactions with medications like blood thinners. The supplements may also worsen conditions such as diabetes and glaucoma, and evidence on their effectiveness remains inconsistent.

Key Points

Mild Side Effects: Common complaints include nausea, diarrhea, constipation, heartburn, bloating, and headache.
Allergy Risk: Individuals with shellfish allergies should avoid most glucosamine supplements, which are often derived from shellfish.
Drug Interactions: Glucosamine and chondroitin can dangerously increase the risk of bleeding in people taking anticoagulant medications like warfarin.
Variable Effectiveness: Scientific evidence on their effectiveness for osteoarthritis is inconsistent and contradictory, with some studies showing no benefit.
Condition Worsening: Caution is advised for those with diabetes (due to potential blood sugar effects) and glaucoma (possible increase in eye pressure).
Regulatory Gaps: As dietary supplements, they lack strict FDA regulation, leading to potential inconsistencies in product quality and dosage.

Common Side Effects

While generally considered safe for most people, glucosamine and chondroitin can cause a number of mild side effects, primarily affecting the digestive system. The most frequently reported issues include nausea, diarrhea, constipation, heartburn, stomach cramps, and bloating. Some users also experience headaches, drowsiness, or skin reactions. These are usually temporary, but if they persist, discontinuing use and consulting a healthcare provider is recommended.

Less Common and Serious Side Effects

Though rare, some serious side effects have been reported. These include allergic reactions (especially for those with shellfish allergies), worsening of asthma symptoms, potential effects on liver and kidney function with prolonged use, changes in blood sugar levels (a concern for individuals with diabetes), increased intraocular pressure (a concern for people with glaucoma), irregular heartbeats, and swelling in the legs.

Drug Interactions

One of the most significant disadvantages of glucosamine and chondroitin is their potential to interact with other medications, which can be dangerous for individuals on certain prescription drugs.

Warfarin and Blood Thinners

A serious interaction exists with the blood thinner warfarin (Coumadin). Glucosamine, with or without chondroitin, can increase the effects of warfarin, raising the risk of severe bruising and bleeding. Medical supervision is necessary in such cases.

Other Medication Interactions

Diabetes medications: Glucosamine may affect blood sugar, potentially reducing the effectiveness of diabetes drugs. Diabetics should monitor blood sugar closely and consult their doctor before using these supplements.
Acetaminophen: Some studies suggest a potential reduction in effectiveness for both glucosamine sulfate and acetaminophen when taken together.
NSAIDs: While not a direct interaction, individuals using these supplements as an alternative to NSAIDs should be aware that their efficacy varies and they don't replace NSAIDs' anti-inflammatory effects.

Questionable Effectiveness and Inconsistent Research

Despite their popularity, scientific evidence on the efficacy of glucosamine and chondroitin is inconsistent, leading to conflicting recommendations.

Mixed Study Results: Large studies have shown mixed results regarding effectiveness for osteoarthritis pain and function. Some studies show modest benefit, while others find no significant difference compared to placebo.
Inconsistent Quality: As dietary supplements, they are not regulated as drugs by the FDA, meaning purity and strength can vary between brands.
Specific Types: Some research indicates specific forms, like pharmaceutical-grade glucosamine sulfate, might be more effective.

Comparison Table: Potential Risks vs. Perceived Benefits


Feature	Disadvantages of Glucosamine and Chondroitin	Potential Benefits of Glucosamine and Chondroitin
Side Effects	Common GI issues (nausea, diarrhea), allergic reactions (shellfish), headache, drowsiness	Generally well-tolerated by most, with minimal side effects in some studies
Drug Interactions	Significant risk with blood thinners (warfarin); potential issues with diabetes medications and acetaminophen	No significant interactions reported for many users on a limited medication regimen
Effectiveness	Conflicting and inconsistent research; many studies show little or no benefit for osteoarthritis	Some individuals report modest relief from joint pain, particularly those with mild-to-moderate osteoarthritis
Regulation	Lack of FDA oversight results in variable product quality, purity, and potency	Supplements are widely available without a prescription for convenient access
Contraindications	Not recommended for individuals with shellfish allergies, glaucoma, or severe kidney/liver disease	May be an option for those seeking a non-NSAID approach for joint discomfort

Conclusion

While many use glucosamine and chondroitin for joint health, understanding their potential disadvantages is crucial. These include side effects ranging from mild digestive issues to more serious concerns like allergic reactions and worsening chronic conditions. A significant risk is the interaction with blood-thinning medications such as warfarin. Furthermore, the inconsistent research on their effectiveness means not everyone will benefit. Consulting a healthcare professional is essential to weigh these disadvantages against uncertain benefits, especially with pre-existing conditions or other medications. Prioritize evidence-based treatments and inform your medical team about supplement usage. For information on supplements, the National Institutes of Health (NIH) is a reliable resource.***

What are the disadvantages of glucosamine and chondroitin?

Frequently Asked Questions

Yes, glucosamine and chondroitin can interact with several medications, most notably blood thinners like warfarin, which can increase the risk of bleeding. They may also interfere with diabetes medications and acetaminophen.

Individuals with shellfish allergies should avoid most glucosamine supplements. Those with diabetes, glaucoma, or severe kidney or liver disease should also exercise caution and consult a healthcare provider before use.

No, research on the effectiveness of these supplements is inconsistent. Some people report mild relief, while many studies show no significant improvement over a placebo, especially for hip and knee osteoarthritis.

Yes, common side effects include mild gastrointestinal issues such as nausea, diarrhea, heartburn, and bloating. Headaches and drowsiness have also been reported.

Glucosamine has been shown in some studies to potentially increase blood sugar levels. Patients with diabetes should monitor their blood sugar closely if taking these supplements and should do so under medical supervision.

Yes, since they are sold as dietary supplements and are not strictly regulated by the FDA, the quality, purity, and actual content can vary considerably between different brands and products.

While often used for up to two years without major safety issues, long-term safety is not fully established. There are some reports of potential long-term effects on kidney and liver function with prolonged use, warranting medical monitoring.