There have been no reported side effects from I’m-Yunity®. As you want to provide the best for your loved pet, we do recommend that you speak with your vet to confirm that your dog isn’t on any medications that suppress the immune system or that your dog does not have an autoimmune disease as I’m-Yunity® is a product to support and help maintain a healthy immune system. If your dog has a mushroom allergy, then this product might not be right for your dog.