Glucosamine appears to be overall safe and with minimal side effects at its most common dosage of 1500 mg a day. One systematic review of randomized controlled trials found no significant difference in the frequency of reported side effects between participants taking glucosamine and those in the placebo group. Although no serious side effects were reported, most adverse events associated with glucosamine supplementation affect the gastrointestinal tract (e.g., diarrhea, abdominal pain, nausea).[1][2]
There are no known interactions between glucosamine and medications. However, there was one reported case where glucosamine appeared to enhance the anticoagulant effect of warfarin, therefore increasing the risk of bleeding and bruising.[3] It’s important to note that this was an isolated case, and the person involved was taking a combination of glucosamine and chondroitin, which may also have been responsible for the interaction.
Additionally, animal studies observed an increase in insulin resistance after the administration of glucosamine. Clinical studies administering glucosamine intravenously have confirmed these results. However, this effect occurs at plasma concentrations higher than those achieved with oral supplementation, and to a lesser degree than observed in rat studies.[4] Other clinical studies have concluded that glucosamine supplementation does not impact insulin sensitivity, so more research is needed to clarify these potential effects.