Dear Dr. Fox • My German shepherd mix is about 3 years old. We adopted her when she was about 10 weeks old and gave her lots of TLC.

Until recently she was a friendly, outgoing and trustworthy dog. But now it's like a shadow comes over her, and she gets spooky and snappy. She pants a lot, gets sweaty and seems possessed. She also scratches more than she used to.

I thought of obedience school after the vet couldn't find anything wrong with her. He suggested trying Prozac if she does not improve with more TLC. Help! — M.W., Houston

Dear M.W. • I sympathize with you not being able to find the cause of your young dog's change in temperament.

Ruling out some backyard trauma while she was out and you were not present, or a change in the home social environment, I would ask your veterinarian to run a full thyroid profile.

Thyroid dysfunction causing aberrant behavior and seizures is reaching near epidemic proportions in dogs, according to my friend, Dr. W. Jean Dodds. In the fall 2011 edition of the excellent new journal "Integrative Veterinary Care," she notes that hypothyroid disease often appears around puberty. The disease afflicts young dogs like yours, who show behavioral changes, including seemingly schizophrenic behavior. Some breeds are especially prone, notably the German shepherd, Doberman pinscher, English springer spaniel, Akita, golden retriever, Rottweiler and Shetland sheepdog.

According to Dr. Dodds, hereditary autoimmune destruction of the thyroid gland accounts for 90 percent of cases of hypothyroidism in purebred and hybrid dog breeds.

After blood tests to confirm the diagnosis, Dr. Dodds recommends treatment twice daily with thyroxine at a dose level according to your dog's weight. Relief should be evident in a few days.

There are many chemical contaminants in our environment, food and water that are identified as endocrine disruptors, which I believe could play a significant role in this near epidemic. For details, check my website, www.twobitdog.com/DrFox.

Thanks to pioneers in the field of integrative veterinary care like Dr. Dodds, we are witnessing a revolution in cost-effective diagnoses, treatments and disease prevention in both human and companion animal medicine. I document this in my new book, "Healing Animals and the Vision of One Health" (CreateSpace).

In the light of Dr. Dodd's findings, I would like to revise my diagnosis of schizophrenia in a Doberman pinscher that I made some 30 years ago after his owner had taken him to many veterinarians who could find nothing wrong.

A couple of thyroid pills a day might have been the answer.

www.twobitdog.com/DrFox Write to: Dr. Michael Fox in care of Universal Uclick, 1130 Walnut St., Kansas City, Mo. 64106.