Glucosamine is an amino derivative of glucose that is used in the building and maintenance of healthy cartilage. Harmful side effects of glucosamine are minimal. A form of glucosamine that has been stabilized with a mineral salt — known as glucosamine sulfate — is used as a dietary supplement to treat osteoarthritis. Studies conducted since the 1980s have reported that the most common side effects are digestive problems, changes in blood pressure or insulin levels, drowsiness or insomnia, increased bleeding risk, and problems from shellfish allergies. Pregnant or nursing women should not take glucosamine supplements due to the lack of studies on the effect that supplements have on fetal development.
The most common side effects of glucosamine are a variety of digestive problems. This was the most frequent complaint among study participants. Nausea, stomach pain, and heartburn were all reported symptoms. Taking glucosamine with meals helped those taking the supplements to avoid gastric problems. Paradoxically, some reported being constipated while others had diarrhea or soft stools.
Since glucosamine is technically a carbohydrate, it may alter levels of blood sugar. Also, glucosamine sulfate can decrease the metabolic actions of insulin. Diabetics are urged to be careful about checking their blood sugar levels while on this supplement. When combined with chondroitin, glucosamine sometimes has changed blood pressure or heart rate — this is one of the side effects of glucosamine that should be monitored.
People who have bleeding disorders or who are taking anti-clotting medicine generally are advised to be careful when taking glucosamine. Also, people who are taking other products like ginkgo or vitamin E should be aware that these can also increase the risk of bleeding. Medical supervision can be a good idea for people who have a bleeding disorder or are taking a product that decreases the blood’s clotting ability.
Sleep problems have been reported by some individuals who are taking glucosamine sulfate. This side effect generally was not serious, but participants in studies reported some drowsiness during the day or nighttime insomnia. A few people also had headaches.
Allergic side effects of glucosamine can be a concern because the most common source of supplements is from shellfish, such as lobsters or crabs. People who are allergic to shellfish are usually advised not to take glucosamine as a dietary supplement. Those people who are allergic to shellfish, however, can take a glucosamine supplement that is made from a grain source, such as corn. Since this information is not always on the packaging, individuals may need to check with the manufacturer to determine the origin of the glucosamine supplement.