Glucosamine is a widely used dietary supplement for joint health, particularly among people with osteoarthritis. Whilst generally well-tolerated, some users report gastrointestinal side effects, including changes in bowel habits. Does glucosamine cause constipation? This article examines the evidence surrounding glucosamine and constipation, explores why digestive disturbances may occur, and provides practical guidance on minimising side effects. Understanding the potential adverse effects of glucosamine helps you make informed decisions about supplementation and recognise when to seek medical advice. Always consult your GP or pharmacist before starting glucosamine, especially if you have existing health conditions or take other medications.

What Is Glucosamine and How Does It Work?

Glucosamine is a naturally occurring compound found in healthy cartilage, particularly in the fluid surrounding joints. As a dietary supplement, it is commonly derived from shellfish shells or produced synthetically in laboratories. In the UK, glucosamine products are available both as food supplements and as licensed medicines, primarily used by individuals seeking to manage symptoms of osteoarthritis, particularly in the knees, hips, and hands.

The proposed mechanism of action centres on glucosamine's role as a building block for glycosaminoglycans and proteoglycans, which are essential components of cartilage matrix. Theoretically, supplementation may help maintain cartilage structure and potentially slow degenerative changes in osteoarthritic joints. Glucosamine is thought to stimulate chondrocyte metabolism and may possess mild anti-inflammatory properties, though the exact mechanisms remain incompletely understood.

Glucosamine supplements are typically available in two main forms: glucosamine sulphate and glucosamine hydrochloride. Glucosamine sulphate is the most extensively studied formulation and is often combined with chondroitin sulphate in commercial preparations. The typical studied dose for medicinal products is 1,500mg daily, usually taken as a single dose or divided throughout the day.

It is important to note that NICE guideline NG226 does not recommend glucosamine for osteoarthritis management due to inconsistent evidence of clinical benefit. Patients considering glucosamine should discuss its use with their GP or pharmacist, particularly if they have existing health conditions or take other medications. Always check product labelling to determine whether you are purchasing a food supplement or a licensed medicine, and to confirm the source (shellfish-derived or vegetarian).

Common Side Effects of Glucosamine Supplements

Glucosamine is generally considered well-tolerated by most individuals, with the majority of users experiencing no adverse effects. However, like all supplements and medications, glucosamine can cause side effects in some people. The most frequently reported adverse effects involve the gastrointestinal system, which is unsurprising given that glucosamine is taken orally and passes through the digestive tract.

Common gastrointestinal side effects include:

• Nausea and indigestion – some users report mild stomach discomfort or feelings of nausea, particularly when taking glucosamine on an empty stomach

• Diarrhoea – loose stools or increased bowel frequency can occur, though this typically resolves with continued use or dose adjustment

• Constipation – changes in bowel habits including constipation are recognised in UK product information

• Abdominal pain or bloating – mild cramping or a sensation of fullness may develop in susceptible individuals

• Heartburn – acid reflux symptoms have been reported, particularly with higher doses

Beyond gastrointestinal effects, other less common side effects may include headache, drowsiness, skin reactions, and rarely, allergic responses. Individuals with shellfish allergies should avoid shellfish-derived glucosamine products and consider synthetic or vegetarian alternatives instead. Those with diabetes or impaired glucose tolerance should monitor blood glucose levels while taking glucosamine.

Serious adverse effects are rare. However, glucosamine may enhance the effect of warfarin, potentially increasing INR and bleeding risk. The MHRA advises that patients taking anticoagulants should consult their healthcare provider before starting glucosamine and ensure appropriate monitoring. Caution is also advised in people with asthma. Glucosamine is not recommended during pregnancy or breastfeeding, or for those under 18 years of age.

If you experience any suspected side effects, report them via the MHRA Yellow Card scheme. If side effects persist or are severe, discontinue use and seek medical advice promptly.

Does Glucosamine Cause Constipation?

Constipation is a recognised gastrointestinal side effect of glucosamine, though it is generally infrequent. UK product information for licensed glucosamine medicines lists constipation among possible adverse reactions, although it does not affect the majority of users.

Several factors may influence whether someone experiences constipation when taking glucosamine:

Firstly, many glucosamine supplements contain additional ingredients such as chondroitin, calcium, or various excipients and binding agents. Calcium, in particular, is a well-recognised cause of constipation, and some formulations may contain significant amounts. Secondly, individuals taking glucosamine for joint pain may have reduced mobility due to osteoarthritis, and decreased physical activity is a well-established risk factor for constipation.

Additionally, people starting glucosamine supplements may be older adults who are already at increased risk of constipation due to age-related changes in bowel function, concurrent medications (such as opioid analgesics, calcium channel blockers, or anticholinergic drugs), or inadequate fluid and fibre intake. The temporal association between starting glucosamine and developing constipation may therefore be coincidental rather than causal in some cases.

If you develop constipation after starting glucosamine, practical steps include taking the supplement with food, reducing or dividing the dose, reviewing the product's excipients, or temporarily stopping the supplement to see if symptoms resolve. Also review your medication list, assess your fluid intake, dietary fibre consumption, and activity levels.

If constipation persists despite self-care measures, or if you experience severe abdominal pain, rectal bleeding, unexplained weight loss, or persistent vomiting, contact your GP for assessment and advice.

How to Prevent Digestive Issues When Taking Glucosamine

If you choose to take glucosamine supplements, several practical strategies can help minimise the risk of gastrointestinal side effects, including any potential bowel disturbances:

Timing and administration:

• Take glucosamine with food – consuming the supplement with meals can significantly reduce nausea, indigestion, and stomach discomfort

• Start with a lower dose – if you're new to glucosamine, consider beginning with half the recommended dose and gradually increasing over one to two weeks to allow your digestive system to adjust

• Divide the daily dose – rather than taking 1,500mg once daily, split it into two or three smaller doses throughout the day

Lifestyle and dietary measures:

• Maintain adequate hydration – aim for 6-8 glasses of fluid daily (water, lower-fat milk, sugar-free drinks) to support healthy digestive function and help prevent constipation

• Ensure sufficient dietary fibre – consume plenty of fruits, vegetables, whole grains, and legumes to promote regular bowel movements (aim for 30g of fibre daily)

• Stay physically active – regular exercise, even gentle walking, stimulates intestinal motility and helps prevent constipation

Product selection and monitoring:

• Choose high-quality supplements – select products from reputable manufacturers that comply with UK quality standards

• Check the ingredient list – be aware of additional components that might affect digestion, particularly calcium or magnesium compounds

• Consider alternative formulations – if one type of glucosamine causes problems, switching between glucosamine sulphate and hydrochloride may help

When to seek medical advice:

Contact your GP or pharmacist if digestive symptoms persist despite self-care measures, worsen over time, or significantly impact your quality of life. Similarly, if you develop severe abdominal pain, blood in stools, unexplained weight loss, or persistent vomiting, seek prompt medical assessment.

Remember that people taking anticoagulants (including warfarin), those with diabetes, asthma, during pregnancy/breastfeeding, or with shellfish allergies should consult a healthcare professional before or while taking glucosamine. Report any suspected side effects via the MHRA Yellow Card scheme.

Frequently Asked Questions