Whether your dog has inflammation, arthritis or endocrine disorders such as Addison’s disease, your veterinarian might have prescribed prednisone or prednisolone for your dog. Before we explain what these drugs are and their functions. This Site Might Help You. RE: My dog was started on Prednisone 20mg on Tuesday & now he is VERY lethargic. Can someone help me? It was rx for SEVERE skin allergies. However, you should be careful not to confuse a lethargic dog with a relaxed dog. A relaxed dog will still come when you call them, eat and drink normally, play with toys and respond to commands. A relaxed dog will still come when you call them, eat and drink normally, play with toys and respond to commands. Our dog has been on Prednisone twice, the first time because he had developed AIHA and the second because a tumor was discovered on his lung. In both instances, when he first started taking it, his reaction was just the opposite of lethargy. Dog lethargy can be caused by many different conditions or illnesses. Some symptoms might include anemia, heart or respiratory conditions, inflammation or infection, dehydration, or hormonal changes. Administration of prednisone can make your dog feel excessively thirsty. Besides this, it may also increase his/her appetite. This results in frequent urination and abnormal weight gain in dogs. Besides this, it may also increase his/her appetite. Lethargy and weakness-- these are vague but common symptoms of illness in dogs. And many things, some of them quite serious, can make your dog weak or lethargic. It's hard not to notice when your normally energetic dog is suddenly lethargic and sleeps all day. Learn more about exercise intolerance and lethargy in dogs. If your dog was recently prescribed prednisone, you may be wondering about prednisone side effects in dogs. Among the variety of medications prescribed to dogs, prednisone is one that is commonly known to cause side effects. My vet prescribed 20 MG of Prednisone Q12H last week. Immediately my dog appeared to be having an adverse reaction. as he was panting, nervous and shaking.