In rats, giving the peptide semax during the first three weeks after birth changes how they behave as teenagers and adults: a dose in the first week makes them explore less later, while doses in weeks two or three make them explore more. No matter when it’s given, it also lowers anxiety and improves learning when they grow up. These results come from newborn rats, not humans, and they don’t tell us how to use semax safely or effectively in adults.

Long-lasting behavioural effects of chronic administration of synthetic ACT(4-10) analogue Semax (MEHFPGP) during early neonatal life were studied. The peptide was injected daily intraperitoneally in dose 0.05 mg/kg during the first, second or second-third weeks of postnatal development. It was shown that the peptide injections during the first week lead to a decrease and during second or second-third weeks--to an increase of exploratory activity in 4-8-week aged rats. Furthermore, the peptide adminictration at all times diminished anxiety and improved learning ability of adult rats. The data obtained show that Semax neonatal administration during the first three weeks of life modulates development of brain structures involved in regulation of exploration, anxiety and learning.