Hi thanks for asking. Clinical studies have consistently reported that glucosamine appears safe. However, a recent Université Laval study shows that people taking glucosamine tend to go beyond recommended guidelines, as they do not feel any positive effects from the drug. Beyond recommended dosages, researchers found in preliminary studies that glucosamine may damage pancreatic cells, possibly increasing the risk of developing diabetes. Adverse effects, which are usually mild and infrequent, include stomach upset, constipation, diarrhea, headache and rash. Since glucosamine is usually derived from the shells of shellfish while the allergen is within the flesh of the animals, it is probably safe even for those with shellfish allergy. However, many manufacturers of glucosamine derived from shellfish include a warning that those with a seafood allergy should consult a healthcare professional before taking the product.Alternative, non-shellfish derived forms of glucosamine are available. thanks.