1. A method of treating a neurological condition in a subject, comprising: administering to a subject in need thereof a composition containing an extract from a Nerium species or a Thevetia species in an amount effective to treat said neurological condition, wherein the extract does not include oleandrin and nerifolin and contains a polysaccharide in less than 1% by weight. 2. A method for treating a neurological condition in a subject in need thereof, comprising: determining whether or not the neurological condition in the subject is Alzheimer's disease, Huntington’s disease, stroke, taupathy or a pathological condition having an etiology associated with excessive proteolysis of the beta-amyloid precursor protein , with the accumulation of beta-amyloid protein in the synapses of neurons in the subject, with the formation of amyloid fibrils in the synapses of neurons in the subject, or with the formation of amyloid plaques in the synapses of neur new to the subject； administration of an unfractionated extract or extract fraction or subfraction of an extract from Nerium species or Thevetia species, where the extract, its fraction or subfraction does not include oleandrin and nerifolin, and contains a polysaccharide in an amount of less than 1% by weight； administration of an initial dose extract to the subject in accordance with the prescribed initial dosing regimen for a certain period of time； periodically determining the adequacy of the clinical and / or therapeutic response of the subject to treatment with the extract； if the subject's clinical and / or therapeutic response is adequate, treatment with the extract is continued as necessary until the desired clinical result is achieved； or, if1. Способ лечения неврологического состояния у субъекта, включающий: введение субъекту, нуждающемуся в этом, композиции, содержащей экстракт из вида Nerium или вида Thevetia в количестве, эффективном для лечения указанного неврологического состояния, где экстракт не включает о
