Glucosamine helps build and repair cartilage. Some people may take glucosamine supplements to boost their joint health. However, while it is likely safe, some people may experience mild side effects.

Glucosamine is a natural sugar that exists in the fluid around the joints, as well as in animal bones, bone marrow, shellfish, and fungi.

The glucosamine in supplements usually comes from the shells of shellfish, though there is also a synthetic form.

According to the National Center for Complementary and Integrative Health, around 2.6% of adults in the United States used supplements of glucosamine, chondroitin, or both in 2012. Chondroitin is similar to glucosamine and also occurs naturally in joints.

These were the second most popular dietary supplement after fish oil and other types of omega-3 fatty acids.

However, experts have questioned whether glucosamine supplements are useful, citing a lack of scientific evidence.

In this article, we explain what glucosamine is, why people take it, and whether research indicates that the supplements can help. We also look at some possible side effects and other risks.

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There is no conclusive evidence that glucosamine supplements can prevent or treat any conditions.

Glucosamine supplements typically come as tablets or capsules, but they are also available as injections.

Also, there are various types of glucosamine, and it is not clear whether they have different effects.

The types include:

  • glucosamine sulfate
  • glucosamine hydrochloride
  • N-acetyl glucosamine

Some supplements combine glucosamine with other ingredients, such as chondroitin sulfate, shark cartilage, or methylsulfonylmethane, known as MSM.

Some people say that these supplements help with joint pain, but there is not enough scientific evidence to confirm this.

The American College of Rheumatologists and the Arthritis Foundation advise people not to use glucosamine or chondroitin sulfate supplements for osteoarthritis. While they are likely to be safe for most people, experts have not confirmed that they work.

It is important to keep in mind that the Food and Drug Administration (FDA) do not regulate the production of glucosamine products or any other supplements. As a result, it is not possible to know exactly what they contain.

Supplements do not always, for example, contain the ingredients listed on their labels. Tests have shown that the glucosamine content in supplements can range from zero to over 100% of the amount advertised.

Also, in some cases, labels listed glucosamine hydrochloride when the supplements contained glucosamine sulfate.

The body uses glucosamine to build and repair cartilage. Cartilage is a flexible, tough, rubbery connective tissue that protects the bones in the joints. It provides padding and prevents the bones from rubbing together.

As people age, their cartilage can become less flexible and start to break down. This can lead to pain, inflammation, and tissue damage, which, for example, occurs in osteoarthritis.

There is some evidence that glucosamine might slow this process and benefit cartilage health.

Glucosamine occurs naturally in the body, but levels fall as people get older. In time, the reduction could contribute to joint deterioration.

People take glucosamine sulfate supplements for many reasons, including:

However, there is not enough evidence to show that it is effective in treating or preventing any of these conditions.

Does glucosamine help with osteoarthritis?

Many people take glucosamine supplements for osteoarthritis, especially that of the hip or knee. Some studies have indicated that it might help reduce pain and improve function.

However, results have varied, and scientists have not been able to identify how glucosamine supplements work, if indeed they do.

Some experts have suggested that any success could be due to a placebo effect, in which simply taking a supplement makes a person feel better.

Current guidelines do not recommend using glucosamine or chondroitin for osteoarthritis. This is because there is not enough evidence to show that they are safe or effective.

Can a placebo help people with chronic pain?

People use glucosamine to help treat or prevent a range of conditions, but scientific investigations into these uses have tended to be inconclusive or have found the supplement to be ineffective.

Some research in animals or human participants has indicated that specific forms of glucosamine may help:

There is no evidence, however, that glucosamine has any effect on chronic lower back pain, for example.

Side effects of glucosamine appear to be mild and infrequent, but they can include:

The National Institutes of Health (NIH) note that oral glucosamine supplements are “likely safe” when taken correctly and by adults, but that some people have experienced mild side effects, including drowsiness, skin reactions, and headaches.

They report that the injectable form is “possibly safe” when administered into muscle twice a week for up to 6 weeks.

Glucosamine may not be suitable for everyone, particularly for people who are dealing with:

Pregnancy and breastfeeding: It is not advisable to use glucosamine at these times, as its effect is unknown.

Cancer: Some supplements reduce the effectiveness of cancer treatment. If you are undergoing this type of treatment and wish to use glucosamine, speak to a doctor first.

Diabetes: One study found that glucosamine supplements might affect glucose levels in the body. This could make them unsuitable for people with diabetes or glucose intolerance.

Asthma: In 2008, authors of a study warned that glucosamine might trigger various adverse effects, including shortness of breath in people with asthma.

Allergies: Glucosamine products derived from shellfish may trigger allergic reactions.

Blood and circulation issues: Glucosamine may also affect blood pressure and blood clotting. People who take it should:

  • avoid using glucosamine with warfarin (Coumadin) and other blood thinners
  • monitor their blood pressure if they are using glucosamine

Oral glucosamine supplements appear to be relatively safe for adults without asthma, allergies, or diabetes, and for those who are not pregnant or breastfeeding.

However, conclusive evidence that it can treat joint complaints and other health issues is currently lacking.