henry copeland:

Ritalin Use in Childhood Has Long-Term Effects on the Brain

The initial scans revealed that the brains of subjects who began taking Ritalin before the age of 16 (the “early treatment” group) had lower levels of GABA — a neurotransmitter linked to inhibition control and often implicated in the neurological makeup of ADHD — than did those who started stimulants later or never took them all. After Ritalin was administered, however, and the patients re-scanned, only the early treatment group saw any increase in GABA levels.
- www.additudemag.com