Glucosamine and chondroitin are generally well tolerated in healthy adults. Some people experience mild digestive discomfort, nausea, or loose stools when first starting, particularly if taken on an empty stomach, so taking this supplement with food is advisable. Glucosamine is commonly derived from shellfish, so people with a shellfish allergy should check the product label carefully before use. If you are pregnant, breastfeeding, have diabetes, or take blood-thinning medication such as warfarin, speak to your GP before use.