Dogs can eat black licorice in moderation. The sugar content of candy licorice can be unhealthy for dogs, and glycyrrhizin, a chemical found in black licorice, can be harmful if consumed in large quantities.
Glycyrrhizin stimulates the adrenal glands and may cause hypertension, water retention, sodium retention and low potassium levels. If your dog eats a piece or two of licorice, adverse effects are unlikely. If your dog consumes a large quantity of licorice, a trip to the veterinarian is advised. The effects of glycyrrhizin build over time, so licorice should not be a regular treat for any dog.
Glycyrrhizin is found in the root of the licorice plant. Herbal licorice can be used as an anti-inflammatory agent and is sometimes prescribed for dogs with arthritis or skin disorders.