Glucosamine can be found naturally in most human and animal tissues, but its highest concentrations are in bones, joints, and cartilage.

However, the primary source of supplemental glucosamine sulfate is shellfish shells. They are a natural source of glucosamine in the form of chitin. Manufacturers process the chitin from the shells of these animals via a method called hydrolyzation.

Some manufacturers also produce glucosamine from non-animal sources such as fermented corn to provide supplements suitable for vegans, vegetarians, and individuals with intolerance or hypersensitivity to shellfish.

Two primary forms of glucosamine are found in supplements - glucosamine sulfate and glucosamine hydrochloride. Both can be derived from either shellfish or via fermentation.

Both glucosamine HCl and sulfate will undergo hydroxylation in your intestinal tract to form free glucosamine, which then goes into your bloodstream and reaches your joints.

However, studies suggest that glucosamine sulfate is much more effective when compared to glucosamine hydrochloride. 

In fact, glucosamine hydrochloride appeared to be utterly ineffective in one meta-analysis, which directly compared the benefits of the two forms [6]. In comparison, glucosamine sulfate showed significant benefits in patients with joint problems.

That is likely because of the higher bioavailability of glucosamine sulfate, which is about 6-fold higher than the bioavailability of glucosamine hydrochloride, according to studies [7]. Therefore, glucosamine sulfate is the more popular and effective form of glucosamine.

Does glucosamine really work for your joints?

As previously mentioned, glucosamine works to reduce arthritis complaints by slowing down the degradation of joint cartilage, reducing pain, and improving joint lubrication and mobility.

Numerous studies and meta-analyses have confirmed that supplementation with glucosamine, either alone or in combination with other dietary substances, can significantly improve pain and mobility.

One of the most recent meta-analyses covered ten clinical trials and a total sample size of more than 3800 participants with knee osteoarthritis [10]. According to the researchers, glucosamine supplements led to a significant reduction in joint pain compared to the placebo group.

The participants who were given glucosamine also achieved reduced joint narrowing by an average of 0.2 mm less than the control group. 

Another meta-analysis by the highly reputable scientific organization Cochrane reported that glucosamine supplementation led to a 28% reduction in pain and about 21% improvement in functionality [11]. 

The researchers deduced these results using data from 20 trials and 2570 participants with knee osteoarthritis.

Overall, the research shows that glucosamine supplementation has a significant benefit for joint health and mobility. Yet, it may take several months of supplementation before there is a noticeable reduction in pain and discomfort.

A meta-analysis of randomized controlled trials published over a period of 22 years revealed that it might take up to 4 months until there is a significant improvement in the symptoms [12].

Moreover, the benefits of reducing pain and improving mobility continue to compound with prolonged supplementation, reaching a maximum after three years of taking glucosamine daily.

To maximize the effectiveness of glucosamine, it is best to start supplementation as early as possible since its primary benefit is slowing down cartilage breakdown and reducing inflammation.

Can you take glucosamine if you have a shellfish allergy?

Because glucosamine sulfate is often sourced from shellfish shells such as shrimp, crab, or lobster, people with shellfish allergies often avoid it for fear of hypersensitivity reactions.

Indeed, there are reports about people with shellfish allergy who have experienced severe adverse effects after taking glucosamine supplements. 

A report also suggests a link between taking glucosamine and an increased incidence of asthma attacks [14].

Yet, recent studies in patients with shellfish allergy reveal that taking a glucosamine supplement does not trigger any hypersensitivity reactions even 24 hours after the supplementation [15].

The American Academy of Allergy, Asthma, and Immunology also declares that people with shellfish allergies can safely take and tolerate glucosamine supplements [16].

That's because most supplements containing glucosamine lack the shellfish's proteins that can trigger an allergic reaction.

Nevertheless, the amount of research on the topic is scarce, so people with shellfish allergies, especially those with life-threatening hypersensitivity, should consult a doctor or medical specialist, such as an allergist, before taking glucosamine.

An allergist may also offer you a medically supervised oral challenge with glucosamine to assess your tolerance.

Note: This article is for informational purposes only and not intended for use as medical advice. Always consult your healthcare provider before starting any dietary supplement.