Dihexa (N-hexanoic-Tyr-Ile-(6) aminohexanoic amide) is a peptide that is stable if administered orally. It is derived from the Angiotensin-IV molecule, which was anticipated to act primarily within the cardiovascular system, but was remarkably found to bind within the central nervous system. It's not only surprising that this peptide can pass through the blood brain barrier, but was also found to be seven orders of magnitude (10,000,000X) more potent that brain-derived neurotrophic factor (BDNF). This has profound implications.
While short term use in rodents seem to be safe, long term effects are totally unknown.