Dihydroergotoxine mesylates, commonly known as ergoloid mesylates, has an FDA-labeled indication for use in the symptomatic therapy of age-related dementia, being employed in individuals over 60 years of age who manifest signs and symptoms of an idiopathic decline in mental capacity. Those who respond are thought to be ones suffering from some process related to aging or have some underlying condition of dementia, such as primary progressive dementia, Alzheimer's dementia, senile onset dementia, or multi-infarct dementia. The mechanism of action of dihydroergotoxine (ergoloid) mesylates in geriatric senility has not been determined.

Am J Pharm Educ. 2006 Oct 15; 70(5): 98.

Although the drug has been in use for several decades (under the brand names Hydergine, Hydergina, Gerimal, Niloric, Redizork, Alkergot, Cicanol, Redergin, Hydrine and others) it's not known how or why it has apparently beneficial effects in some patients.

It's used to treat mood, behaviour, and other problems caused by changes in the brain due to Alzheimer's diseaseplugin-autotooltip__plain plugin-autotooltip_bigAlzheimer's disease

"Alzheimer’s disease is a chronic progressive neuro-degenerative disorder characterised by three primary groups of symptoms. The first group (cognitive dysfunction) includes memory loss, language difficulties, and executive dysfunction (that is, loss of higher level planning and intellectual coordination skills). The second group comprises psychiatric symptoms and behavioural disturbances — for example, depression, hallucinations, delusions, agitation — collectively termed … (or multiple small strokes).

It's now generally thought that its effects may be due to alterations of neuro-transmission within neural synapses, rather than because of its tendency to increase blood flow, as was once assumed.