Side Effects of Dog Health Supplements

Dog health supplements are sometimes necessary for a dog even if his diet is well balanced. However, there are as many side effects to dog health supplements as there are benefits.


Calcium: good for bones and their growth. However, more calcium does not mean stronger, healthier bones. Too much calcium in a dog's body can make the bones too weak and brittle. This is sometimes seen in larger dogs that have big bones that cannot support themselves.

Vitamin E

Vitamin E is important for a dog's muscles, circulatory system and injury healing, and acts as an anti-oxidant. If a dog is taking Vitamin E supplements per a veterinarian's recommendation, he might initially feel lethargic as his body adjusts to it.

Niacin (Vitamin B3)

Niacin is essential to a dog's diet, as it aids with the production of enzymes. This supplement should be given only in small amounts, because too much can be toxic. The side effects of too much niacin in a dog's diet include diarrhea that may have blood, inflammation of the throat and lips, an increase in salivation and convulsions.

Vitamin A

Vitamin A is important for a dog's growth, the support of proteins in the body, vision and immunity. Side effects of this vitamin include toxicity if too much is taken, dehydration, night blindness and weight loss. Other side effects a dog can experience are vomiting, diarrhea, hair loss, muscle weakness and bone deformities.

Vitamin D

Vitamin D is essential for the absorption of calcium, which is why it is often found in dairy products for humans. The sun also provides Vitamin D through its rays. Too much Vitamin D can cause hypercalcemia, a condition that can make a dog's bones weak. Another side effect of Vitamin D is that an excess can cause the destruction of Vitamin E in a dog's body, which will shorten or destroy muscle fibers.

Other side effects of Vitamin D include nausea, diarrhea, dehydration, loss of appetite and general weakness. Vitamin D can also cause a dog's muscles to calcify, and can lead to an increase in urination.

Vitamin B6

Glucose levels, the function of red blood cells, a dog's immunity, hormones and nervous system are all affected by the level of B6 in a dog's body. Side effects of this supplement are muscle weakness, loss of balance and coordination, and convulsions.


Sodium is beneficial in the balancing of electrolytes and osmotic pressure in a dog. Side effects related to sodium include an increase in a dog's heart rate and blood pressure. Sodium can also cause a dog to feel thirstier and have dry mucous membranes.


Thyroid function is dependent upon how a dog's body produces iodine and synthesizes it. It helps control a dog's metabolism and aids in a puppy's growth. The side effects of iodine, especially if too much is given to a dog, is an enlargement of the thyroid gland as a result of hyperthyroidism, a dry coat, weight loss and dry skin. A dog may also become thirstier and eat more than usual.

Supplements are a great way to add needed nutrients into a dog's diet if a substance is missing. Because of the potential side effects and toxicity of some supplements, one should always consult a vet before giving his dog extra nutrients.