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. 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.
Side Effects and Warnings
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 no effects on blood sugar, while other research reports effects on insulin. 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, abnormal increased 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. 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.
Preliminary data suggest that glucosamine may modulate the immune system, although the clinical relevance of this is not clear.
Pregnancy & Breastfeeding
Glucosamine is not recommended during pregnancy or breastfeeding due to lack of scientific evidence.
Adults (18 years and older)
In most available studies, 500 milligrams of glucosamine sulfate has been used, 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.
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.
Children (younger than 18 years)
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.
Interactions with Drugs
In theory, glucosamine may decrease the effectiveness of insulin or other drugs used to control blood sugar levels. However, there is limited human research to suggest that glucosamine may not have significant effects on blood sugar. Nonetheless, caution is advised when using insulin or drugs for diabetes by mouth. Patients with diabetes should be monitored closely by a qualified healthcare provider, and medication adjustments may be necessary. Based on limited evidence, the combination of glucosamine with diuretics (water pills) such as furosemide (Lasix®) may cause an increased risk of glucosamine side effects.
In theory, glucosamine may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants ("blood thinners") such as warfarin (Coumadin®) or heparin, anti-platelet drugs such as clopidogrel (Plavix®), and non-steroidal anti-inflammatory drugs such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).
In theory, glucosamine may decrease the effectiveness of herbs or supplements that lower blood sugar levels. Caution is advised when using herbs or supplements that may alter blood sugar.
Based on limited human study, side effects of glucosamine may be increased when used at the same time as diuretics herbs or supplements.
In theory, glucosamine may increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding
There are preliminary reports that use of glucosamine with vitamin C, bromelain, chondroitin sulfate, or manganese may lead to increased beneficial glucosamine effects on osteoarthritis. Simultaneous use with fish oil may have additive beneficial effects in the treatment of psoriasis, based on preliminary research.