Vitamin D May Help Avert Alzheimer's Disease, Dementia Small molecule activation of the neurotrophin hepatocyte growth factor to treat Alzheimer disease Dihexa (also known as PNB 0408) is an experimental small molecule derived from angiotensin IV. It was engineered to cross the bloodbrain barrier and has shown synaptogenic effects in preclinical models. The often quoted Is Dihexa an approved and safe treatment for cognitive impairment or neurodegenerative diseases such as Alzheimer disease?