Lynn Zimmer, PhD, Former Professor Emeritus at the Queens College, City University, New York (CUNY), and John P. Morgan, MD, Medical Professor Emeritus at City University of New York Medical School, wrote in their 1997 book Marijuana Myths, Marijuana Facts:

“None of the medical tests currently used to detect brain damage in humans have found harm from marijuana, even from long-term high-dose use….

The claim that marijuana destroys brain cells is based on a speculative report dating back a quarter of a century that has never been supported by any scientific study.”