Dr. Gabriel G. Nahas, a controversial medical researcher who became a prominent crusader against marijuana after being shocked to hear, at a PTA meeting in 1969, about the drug’s widespread use, died on June 28 in Manhattan. He was 92.

The cause was a respiratory infection, his family said.

Dr. Nahas did research to find the physiological effects of smoking marijuana, wrote 10 books on the drug and became a leader of antidrug organizations. He was a visible ally of Nancy Reagan in her “just say no” to drugs campaign as the first lady in the 1980s.

Dr. Nahas saw his antidrug campaign as nothing less than a continuation of the fight against totalitarianism, which for him began during World War II as a decorated leader of the French Resistance; like totalitarianism, he believed, drugs enslaved the mind. He was awarded the Legion of Honor by France, the Presidential Medal of Freedom by the United States and the Order of the British Empire for his wartime heroism.

His research, which he did as a professor at Columbia University and reported in more than 700 articles in scientific journals, suggested that marijuana contributed to cancers of the head and neck, leukemia, infertility, brain damage and a weakening of the immune system. He also wrote two books on cocaine, which he contended could cause irreversible brain damage.