In most available studies, 500 milligrams of glucosamine sulfate has been taken by mouth as tablets or capsules three times daily for 30 to 90 days. Once daily dosing as 1.5 grams (1,500 milligrams) has also been used. Limited research has used 1,500 milligrams daily as a crystalline powder for oral solution or 500 milligrams of glucosamine hydrochloride three times daily. Dosing of 20 milligrams per kilogram of body weight daily has also been recommended in some publications. One study used a dose of 2,000 milligrams per day for 12 weeks.
Another kind of glucosamine that has been used is a topical form in combination with chondroitin for a four-week period. Safety and effectiveness of these formulations are not clearly proven.
Glucosamine hydrochloride provides more glucosamine than glucosamine sulfate, although this difference likely does not matter when products are prepared to provide a total of 500 milligrams of glucosamine per tablet.
There is not enough scientific evidence to recommend the use of glucosamine in children.
Research in children has shown that there could be a relationship between the ingestion of MSM (methylsulfonylmethane) and autism; whether it is beneficial or harmful is unclear. MSM is often marketed with glucosamine as a dietary supplement and at this time should be avoided in children.
Since glucosamine can be made from the shells of shrimp, crab, and other shellfish, people with shellfish allergy or iodine hypersensitivity may have an allergic reaction to glucosamine products. However, some research suggests that there is not enough shrimp allergen in glucosamine supplements to trigger reactions in patients who are allergic to shrimp. Nevertheless, caution is warranted. A serious hypersensitivity reaction including throat swelling has been reported with glucosamine sulfate. There are reported cases suggesting a link between glucosamine/chondroitin products and asthma exacerbations.
In most human studies, glucosamine sulfate has been well tolerated for 30 to 90 days.
Side effects may include upset stomach, drowsiness, insomnia, headache, skin reactions, sun sensitivity, and nail toughening. There are rare reports of abdominal pain, loss of appetite, vomiting, nausea, flatulence (gas), constipation, heartburn, and diarrhea. Based on several human cases, temporary increases in blood pressure and heart rate, as well as palpitations, may occur with glucosamine/chondroitin products. Based on animal research, glucosamine theoretically may increase the risk for eye cataract formation.
It remains unclear if glucosamine alters blood sugar levels. Several human studies suggest that glucosamine taken by mouth has no effects on blood sugar, while other research reports mixed effects on insulin. When glucosamine is injected, it appears to cause insulin resistance and endothelial dysfunction. Preliminary studies show no effect on mean hemoglobin A1c concentrations in patients with type 2 diabetes mellitus. Caution is advised in patients with diabetes or hypoglycemia and in those taking drugs, herbs, or supplements that affect blood sugar. Serum glucose levels may need to be monitored by a healthcare provider and medication adjustments may be necessary.
In theory glucosamine may increase the risk of bleeding. Caution is advised in patients with bleeding disorders or taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary.
In several human cases, abnormally high amounts of protein were found in the urine of patients receiving glucosamine/chondroitin products. The clinical meaning of this is unclear. Glucosamine is removed from the body mainly in the urine, and elimination of glucosamine from the body is delayed in people with reduced kidney function. Acute interstitial nephritis, a condition that causes the kidneys to become swollen and possibly dysfunctional, has been reported in a patient taking glucosamine. Increased blood levels of creatine phosphokinase may occur with glucosamine/chondroitin, which may be due to impurities in some products. This may alter certain laboratory tests measured by healthcare providers.
Early data suggest that glucosamine may modulate the immune system, although the clinical relevance of this is not clear.
Glucosamine is not recommended during pregnancy or breastfeeding due to lack of scientific evidence.