Well, I know they work on the photocycle of the ferret (there is a hypothesis that incorrect lengths of natural daylight contribute to adrenal disease). Melatonin works to change what the body is perceiving as it's natural photoperiod and sleep cycle. (Think about human melatonin and why people take it to prevent jetlag when they travel).
Having said all of that, I'm really not familiar with how successful it is in treating ferrets with adrenal or in preventing adrenal, but I'd assume of those two, the prevention would be more successful.
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"Dogs are followers, cats are self-absorbed, ferrets just are."
