Glucosamine plays a vital role in building cartilage, and many people take it as a supplement to treat arthritis and osteoarthritis. It occurs naturally in the fluid around the joints, in animal bones, bone marrow, shellfish, and fungi.

Glucosamine, especially glucosamine sulfate, is extracted from the shells of shellfish to make dietary supplements. A synthetic form is made in laboratories, also.

In this article, we explain what glucosamine is, why it is taken as a supplement, and whether there is scientific evidence to prove it is effective. We also discuss any side effects and warnings that come with glucosamine.

Glucosamine is normally taken by mouth and comes in different forms, including:

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Glucosamine comes in a number of forms.
  • glucosamine sulfate
  • glucosamine hydrochloride
  • N-acetyl-glucosamine

Although similar, these variants can have different effects when used as dietary supplements.

In some dietary supplements, glucosamine may be combined with other ingredients, including chondroitin sulfate, MSM, or shark cartilage.

Chondroitin is a similar substance to glucosamine and is found naturally in joints, as well.

Some people claim that the combinations in these supplements help, but researchers argue that scientific proof is lacking.

To date, most studies into the potential health benefits of glucosamine focus on glucosamine sulfate.

When buying supplements, it is advisable to do so from reputable outlets. The U.S. National Institutes of Health (NIH) point out that glucosamine sulfate products do not always contain the ingredients listed on their label.

Furthermore, tests have shown that the glucosamine content can range from 0-100 percent. In some cases, the labels may claim the products contain glucosamine hydrochloride, but it is, in fact, glucosamine sulfate.

Glucosamine is vital for building cartilage. Cartilage is a flexible, tough connective tissue found in several parts of the body. This firm, rubbery tissue functions as padding at the ends of long bones where they meet joints.

As we age, cartilage can become less flexible and can steadily breakdown. There is some evidence that glucosamine might slow this process.

Some scientists believe it is the sulfur in glucosamine that is beneficial for cartilage health. Sulfur must be incorporated into cartilage to build and repair it. Naturally, glucosamine plays a role in the incorporation of sulfur into cartilage.

As people age, glucosamine levels fall. So, in time, this may play a role in joint deterioration.

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Some people take glucosamine for joint pain.

According to the National Center for Complementary and Alternative Therapy, a 2007 National Health Interview Survey found that 17.7 percent of adults in the United States regularly took some type of dietary supplement.

Of those, 19.9 percent took glucosamine. It was the second most popular dietary supplement after fish oil, omega 3, or DHA, which were taken by 37.4 percent of those who took supplements.

The NIH list the following reasons why people use glucosamine sulfate:

Glucosamine supplements are also used by people with inflammatory bowel disease (IBD) and ulcerative colitis.

Does glucosamine help with osteoarthritis?

Many people take glucosamine supplements for OA, and especially OA of the hip or knee.

Some studies suggest that glucosamine may have the following effects:

  • Reduce osteoarthritis-related pain, stiffness, and swelling in the joints.
  • Improve function in people with knee or hip osteoarthritis.
  • Provide continued relief of symptoms for up to 3 months after someone stops treatment.

However, the Glucosamine and Chondroitin Arthritis Intervention Trial (GAIT) surveyed 1,600 participants in 16 locations across the U.S. and found that glucosamine plus chondroitin sulfate did not give significant relief from osteoarthritis.

Some participants with moderate-to-severe pain reported significant relief, however, when they took the combination of glucosamine and chondroitin.

While this combination, or glucosamine alone, may relieve moderate to severe pain in people with osteoporosis, overall, it appears to be no more effective than a placebo in slowing the loss of cartilage in knee osteoarthritis.

In a 2005 review of 18 trials, some results indicated that glucosamine or glucosamine sulfate might benefit people with osteoarthritis, while others did not find it significantly effective.

A review of two trials for glucosamine hydrochloride in 2010 did not reveal a clinically significant improvement in joint pain or in the osteoarthritis condition itself.

The NIH point out that while some people use creams containing glucosamine for arthritis pain, these creams usually include other substances, such as camphor. Hence, it may be these additional substances that relieve the pain, and there is no evidence that glucosamine can be absorbed through the skin.

Some studies have suggested that a form of glucosamine may help people with irrigable bowel disease (IBD).

Elsewhere, scientists at the University of California, Irvine, found that N-acetyl glucosamine (GlcNAc) supplements suppressed the damaging autoimmune response that occurs in MS.

It appears that GlcNAc may inhibit the growth and function of abnormal T-cells that mistakenly cause a person's immune system to attack and destroy myelin, the tissue that insulates the nerves.

These findings were supported by a mouse study at Jefferson Medical College. The team found that over-the-counter (OTC) glucosamine helped delay the onset of MS symptoms in mice and improved their ability to move and walk.

A further study found that glucosamine may have a carry-over effect when used with ibuprofen to reduce pain levels in people with temporomandibular joint (TMJ) problems.

Glucosamine has been recommended for a range of conditions and illnesses, but studies have tended to be inconclusive or have found it ineffective or even harmful, for instance, to people with an allergy.

There is no evidence, for example, that it either helps or does not help people with sports injuries or with chronic lower back pain.

There are no scientific studies to suggest that glucosamine is either beneficial or detrimental for people with venous insufficiency, which affects blood flow in the legs.

The American Family Physician warns that people with asthma should use glucosamine with caution, as it has been linked with the breathing condition in some people.

Side effects of taking glucosamine are reported to be mild and infrequent, but they can include:

The NIH note that glucosamine is "likely safe" when used correctly by adults, but that some people have experienced mild side effects, including drowsiness, skin reactions, and headache.

The effect of glucosamine during pregnancy or breastfeeding is unknown, so it is not advisable to use it at these times.

There has been some debate about whether glucosamine raises blood glucose levels in people with diabetes, but studies suggest that in those with type 2 diabetes, it probably does not.

Some people take glucosamine to treat allergies, but glucosamine products derived from shellfish may trigger allergies in anyone who is susceptible. People with a shellfish allergy are advised to avoid this type of glucosamine supplement.

In conclusion, glucosamine is relatively safe when taken as advised, by adults without asthma or allergies. However, evidence for its ability to treat joint complaints and other conditions is currently lacking.