While blueberries are generally safe for dogs to eat in moderation, blueberry muffins may not be the best treat for them. Most commercially prepared blueberry muffins contain ingredients like sugar, butter, and sometimes even chocolate or other harmful additives, which are not suitable for dogs. The main concerns with feeding dogs blueberry muffins are the potential high sugar content, which can lead to obesity and dental issues, and the added ingredients that can be toxic to dogs. If you want to share blueberries with your dog, offer them fresh, plain blueberries in small quantities as an occasional treat. Always consult with your veterinarian before introducing any new foods to your dog's diet to ensure they are safe and suitable for your pet's individual health needs.