The Rat Fan Club



by Debbie Ducommun


Updated 7/6/15


In 2011, I reported on a new treatment for pituitary tumors in the Rat-a-tat Chat, the quarterly newsletter of the non-profit Rat Assistance & Teaching Society (, and here is that report:

An Exciting New Treatment for Pituitary Tumors


            Earlier this year, I heard from a couple of rat owners that their veterinarians had prescribed a drug called cabergoline for rats suspected of having a pituitary tumor. In April, a veterinarian had even emailed me to see if I had heard of cabergoline being used in rats, but it was all new to me. I did some research online and learned that it is a drug used to treat the most common type of pituitary tumor in humans, called a prolactinoma, which is a benign tumor (adenoma) of the pituitary gland that overproduces a hormone called prolactin. The overproduction of prolactin can result in abnormal milk production. At first I thought the cabergoline only reduced the production of prolactin, but apparently it can actually reduce the size of a pituitary tumor, which is very exciting.


            A case study published in the September 1, 2011 issue of the Journal of the American Veterinary Medical Association reported that a male rat with a large pituitary tumor was given about 8 more good months of life through treatment with cabergoline. The 2-year-old unneutered male rat was taken to the Tufts Cummings School of Veterinary Medicine in North Grafton, MA, with a 3-week history of apparent blindness, aggressive behavior and a reduction in water intake. The veterinary exam also found the rat’s hind legs were partial paralyzed. An MRI scan, which was done with the rat anesthetized, showed a large pituitary tumor measuring 11.4 X 8.6 X 8.3 mm (about 7/16 X 5/16 X 5/16 inch—about the size of an unshelled peanut) which was half the length of the rat’s brain. The rat was put on cabergoline at 0.27 mg/lb once every 3 days and there was improvement in his behavior within three days of starting the treatment. Eight weeks later the rat’s behavior had returned to normal and another MRI showed that the tumor was reduced to 41% of its original size, and was now only 8.4 X 6.7 X 5.9 mm (which is still pretty big—about the size of a large raisin).


            The rat apparently did well until eight and half months after the onset of treatment, when he was taken back to the vet with hind leg paralysis, weight loss, and respiratory distress. A third MRI found the tumor had regrown to 9.1 X 8.0 X 7.3 mm, and the rat was euthanized. A biopsy confirmed the diagnosis of a prolactinoma.


            The most common side effects of cabergoline in humans are digestive-related, such as nausea and constipation, or behavioral, such as dizziness, insomnia, or depression. The only medication that interacts with cabergoline that rats might also be given is metoclopramide, a treatment for mega-esophagus, which is a very rare problem.


            Addendum: In February 2015, one of my rats was diagnosed with a pituitary tumor. In the U.S. cabergoline is fairly expensive (it’s much cheaper in Europe), but by using the website I was able to get a one-month treatment for $58 from Wal-Mart. I treated my boy for 2 months, and he did quite well, but then he died from a different problem. I have also heard of several other cases where the cabergoline has helped significantly for several months.

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