Most of the Collagen supplements are generally safe but have potential side effects like digestive issues, nausea and heartburn. Some people have also cited one side effect as feeling of fullness. As stated in our Vitauthority Multi collagen protein Review, this collagen product is dairy-free and gluten-free and does not contain fish and eggs. Collagen is an exciting supplement to give you a boost of benefits. However, it would be best if you always talked to your doctor before trying it out.