Cognitive Dysfunction Syndrome (CDS) is supposed to be caused by physical and chemical changes that affect the brain function in older dogs. Dogs with CDS may show signs of confusion and/or various other behavioral changes that are not a normal part of aging. According to CDSinDogs.com, a Pfizer advertising website, Anipryl (selegiline hydrochloride) may be the answer to recapture the good times between you and your senior dog.
The website recommends that "Senior dogs should be observed more closely, because changes in normal appearance, activity and behavior all can be signs that veterinary attention may be needed. Always contact your veterinarian if you notice anything unusual in your dog's appearance or behavior."
Selegiline can be used in humans in Parkinson's disease, either alone or as adjunct to levodopa with dopa-decarboxylase inhibitor. It has been tested for use in Alzheimer's disease, but there is no evidence of any clinically meaningful effect. To quote from the Cochrane review summary, "Despite its initial promise, i.e. the potential neuroprotective properties, and its role in the treatment of Parkinson's disease, selegiline for Alzheimer's disease has proved disappointing. Although there is no evidence of a significant adverse event profile, there is also no evidence of a clinically meaningful benefit for people with Alzheimer's disease. There would seem to be no justification, therefore, to use it for Alzheimer's disease, nor for any further studies of its efficacy in Alzheimer's disease."
If it's no good in humans, why's it licensed in dogs? I suppose this means it at least has a market.