NPR reports on a study giving volprioc acid to adults and training them on pitch (singing):
Hensch is studying a drug which might allow adults to learn perfect pitch by recreating this critical period in brain development. Hensch says the drug, valprioc acid, allows the brain to absorb new information as easily as it did before age 7.
"It's a mood-stabilizing drug, but we found that it also restores the plasticity of the brain to a juvenile state," Hensch tells NPR's Linda Wertheimer.
Brain plasticity is useful for a whole lot more than learning pitch. As the article notes it would be invaluable for training one's ear to pick up sounds of foreign languages, but also it seems reasonable to this commentator that high levels of plasticity during rationality training or other forms of self-development would result in more transformative results.