From NIH.gov: Studies have found that glucosamine and chondroitin supplements may interact with the anticoagulant (blood-thinning) drug
warfarin (Coumadin). Overall, studies have not shown any other serious side effects.
Also from NIH.gov:
The American Academy of Family Physicians lists patients with shellfish allergy, diagnosis of asthma, or use of diabetes medications or warfarin as “C” evidence contraindications (supported by consensus, disease-oriented evidence, usual practice, expert opinion, or case series). Although not prohibitive to glucosamine sulfate use, patients with one or more of these criteria should be monitored cautiously for potential adverse effects.
Through various studies, Glucosamine sulfate has consistently been concluded to be a relatively safe oral supplement. A few isolated case studies have reported on the incidence of hepatotoxicity following >3 weeks of glucosamine sulfate use. However, all patients cited had severe preexisting liver disease, with one of the eight patients mentioned developing hepatic failure.
The evidence available on the effectiveness of glucosamine sulfate as a beneficial therapy in the management of osteoarthritis is, to date, inconclusive. Interestingly, studies have shown that patients are not deterred from supplement use when presented with data concluding lack of efficacy, with the only evidence of significant toxicity showing to be capable of causing changes in supplement consumption. Physicians should be mindful of this when discussing the benefits and risks of various treatment modalities with OA patients, particularly those of no validated benefit. The physician must personalize the risk and benefits of taking glucosamine sulfate to each patient. Typically, a 60-day trial of glucosamine sulfate will determine if there are beneficial effects, after which it should be discontinued if the patient has not observed any beneficial effect by that time.
From my family members and doctors, glucosamine doesn't really work for joint pain or arthritis.
You are 56yo. That's when pain starts to be part of life and not a sign of a problem, especially if arthritis runs in you or your family. As you get older, your exercise routine and sports need to be changed to prevent injury irrespective of warfarin.
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As you get older, pain helps you know you're still alive in the morning."