Glucosamine is a widely used dietary supplement for joint health, particularly in osteoarthritis management. Whilst generally well tolerated, questions arise about glucosamine side effects on the liver. Although serious hepatic complications are rare, isolated reports of elevated liver enzymes and liver injury have been documented. Understanding potential liver-related risks is essential for safe supplement use, particularly for individuals with pre-existing liver conditions or those taking multiple medications. This article examines the evidence surrounding glucosamine and liver health, identifies warning signs, and provides guidance on safe use in line with UK clinical practice.

What Is Glucosamine and How Does It Work?

Glucosamine is a naturally occurring compound found in cartilage, the tough tissue that cushions joints. As a dietary supplement, it is commonly used to support joint health and manage symptoms of osteoarthritis. In the UK, glucosamine supplements are available over the counter in various formulations, most commonly as glucosamine sulfate or glucosamine hydrochloride, often combined with chondroitin.

Mechanism of action: Glucosamine is theoretically thought to work by providing building blocks necessary for cartilage repair and maintenance. It may stimulate the production of glycosaminoglycans and proteoglycans, essential components of cartilage matrix. Additionally, glucosamine may possess mild anti-inflammatory properties, potentially reducing joint pain and stiffness. However, the evidence for its clinical efficacy remains mixed, with some studies showing modest benefits whilst others demonstrate minimal advantage over placebo.

The typical recommended dose ranges from 1,500 mg daily, usually taken as a single dose or divided throughout the day. Most glucosamine products are sold as food supplements, though some glucosamine sulfate products are licensed as medicines in the UK. However, NHS England advises against routine prescribing of glucosamine on the NHS. It's important to note that NICE guidance (NG226) explicitly advises not to offer glucosamine or chondroitin for osteoarthritis management.

Glucosamine supplements are generally considered safe for short- to medium-term use, with most adverse effects being mild and gastrointestinal in nature. However, concerns have been raised about potential effects on liver function, particularly in individuals with pre-existing liver conditions or those taking multiple medications.

Patients should inform their GP or pharmacist about all supplements they are taking, particularly before starting new medications or if they have existing health conditions.

Recognising Liver-Related Side Effects

Whilst glucosamine is generally well tolerated, there have been isolated reports of liver-related adverse effects in the medical literature. There is no official established link between routine glucosamine use and significant liver damage in healthy individuals, but healthcare professionals should remain vigilant, particularly in susceptible populations.

Reported hepatic effects have included elevated liver enzymes (transaminases), which are markers of liver cell injury. In rare cases, individuals have developed hepatitis or cholestatic liver injury whilst taking glucosamine supplements. These cases are uncommon and causality can be difficult to establish, as many patients taking glucosamine also use other supplements or medications that may affect liver function.

Signs and symptoms that may indicate liver problems include:

• Persistent fatigue or malaise

• Jaundice (yellowing of the skin or whites of the eyes)

• Dark urine or pale stools

• Right upper abdominal pain or discomfort

• Unexplained nausea or loss of appetite

• Itching (pruritus) without rash

If any of these symptoms develop whilst taking glucosamine, patients should discontinue the supplement immediately and contact their GP for assessment. Healthcare professionals may arrange liver function tests (LFTs) to evaluate transaminase levels (ALT, AST), alkaline phosphatase, bilirubin, and other markers of hepatic function.

It is worth noting that most people who take glucosamine experience no liver-related problems whatsoever. The gastrointestinal side effects—such as nausea, heartburn, diarrhoea, or constipation—are far more common than hepatic complications. Nevertheless, awareness of potential liver effects is important for informed decision-making and appropriate monitoring.

Patients should report any suspected side effects to the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or via the Yellow Card app).

Who Should Avoid Glucosamine?

Certain individuals should exercise caution or seek medical advice before taking glucosamine supplements due to potential risks, including rare liver complications. Healthcare professionals should carefully assess patient suitability before discussing glucosamine.

Pre-existing liver disease: Patients with chronic liver conditions such as cirrhosis, hepatitis (viral or autoimmune), non-alcoholic fatty liver disease (NAFLD), or any history of drug-induced liver injury should seek medical advice and consider use only under supervision. The liver's reduced capacity to metabolise substances may increase vulnerability to adverse effects.

Concurrent medications: Individuals taking warfarin or other coumarin anticoagulants should be aware that glucosamine may enhance their anticoagulant effect, increasing bleeding risk. The MHRA has issued safety information about this interaction. Patients on warfarin should have their INR monitored more frequently if taking glucosamine and should inform their anticoagulation clinic.

Shellfish allergy: Many glucosamine supplements are derived from shellfish shells. People with shellfish allergies should either use verified non-shellfish (vegetarian or synthetic) alternatives or avoid glucosamine entirely.

Diabetes: Some evidence suggests glucosamine may affect glucose metabolism, though effects are generally small and inconclusive. Patients with diabetes should monitor blood glucose levels when initiating glucosamine and discuss use with their diabetes care team.

Asthma: Rare cases of asthma exacerbation have been reported with glucosamine use. People with asthma should be aware of this possibility and discontinue use if symptoms worsen.

Severe renal impairment: Caution is advised in people with severe kidney disease, as limited information is available on safety in this population.

Pregnancy and breastfeeding: Due to insufficient safety data, glucosamine is not recommended during pregnancy or whilst breastfeeding unless specifically advised by a healthcare professional.

Children and adolescents: Glucosamine is not recommended for people under 18 years of age.

Safe Use and Monitoring Recommendations

For individuals who choose to take glucosamine supplements, following evidence-based safety practices can minimise potential risks, including liver-related complications.

Before starting glucosamine:

• Consult your GP or pharmacist, particularly if you have existing health conditions or take regular medications

• Disclose all supplements and over-the-counter products you currently use

• Consider baseline liver function tests if you have risk factors for liver disease

• Choose reputable brands that provide clear labelling of ingredients and dosage

During glucosamine use:

• Adhere to recommended dosages (typically 1,500 mg daily); avoid exceeding suggested amounts

• Take glucosamine with food to reduce gastrointestinal side effects

• Monitor for any new or unusual symptoms, particularly those suggesting liver problems

• Keep a symptom diary if you have osteoarthritis to assess whether glucosamine provides meaningful benefit

• Inform all healthcare professionals (including dentists and hospital staff) that you take glucosamine

When to seek medical advice:

• Development of jaundice, dark urine, or persistent right upper abdominal pain

• New or worsening fatigue, nausea, or loss of appetite

• Any unexplained symptoms after starting glucosamine

• If you need to start new medications whilst taking glucosamine

NICE guidance on osteoarthritis management (NG226) advises not to offer glucosamine or chondroitin for osteoarthritis. Instead, NICE recommends a holistic approach including exercise, weight management, education and appropriate pain relief as core treatments.

Monitoring: No routine liver function monitoring is recommended for healthy individuals taking glucosamine. Consider baseline and follow-up testing only if risk factors are present or symptoms develop. For patients taking warfarin, closer INR monitoring is essential if glucosamine is used concurrently.

If no benefit is apparent after 2-3 months of glucosamine use, discontinuation should be considered. Remember to report any suspected side effects to the MHRA Yellow Card scheme.

Frequently Asked Questions