According to a study conducted by neuroscientists at the University of San Diego, weed—unlike alcohol—is not dangerous to the teenage brain. The brains of 92 teenagers were studied over time, and half of the group—who already experimented with marijuana and alcohol—was ordered to either abstain or indulge in moderation for 18 months. The other half continued to drink and smoke in "varying amounts."
The teens were interviewed every six months about their substance use, and researchers compared brain scans before and after drug and alcohol use or abstention. Results showed that teens who drank five or more drinks at least twice a week showed lower white matter brain tissue health. The white matter brain tissue of teens who smoked weed, occasionally as often as nine times a week, did not suffer.
White matter brain tissue health continues to develop into adulthood, and a loss could result in a decline in memory, decision making and attention span into late-adolescence and adulthood.