Generally, dogs should not be given more than 1 teaspoon or one tablet of brewer's yeast per day, according to Vetinfo. The dosing information on the package should be followed, however, because dogs’ sizes should be taken into account when determining dosages.
Dogs with food allergies may have reactions to brewer's yeast, advises Vetinfo. Indications of an allergic reaction are skin rashes and dry, itchy skin. If a dog experiences this, the brewer's yeast should be discontinued. If the rash goes away after discontinuing, it can most likely be attributed to an allergic reaction.
There are brewer's yeast supplements available with garlic added. Garlic can have beneficial health effects for dogs, but can also be toxic in large amounts, explains Vetinfo. One gram of garlic for every 10 pounds of the dog’s body weight is safe. The dosing instructions on the package should be followed.