A prominent emergency room doctor at Mount Sinai Hospital in Manhattan was arrested on Tuesday and accused of drugging, groping and masturbating on a female patient and groping another in separate episodes several months apart, the authorities said.

The charges against the doctor, David H. Newman, 45, a proponent of reforms in emergency care who has written widely about improving doctor-patient relationships, describe him targeting young women for abuse when they sought medical treatment.

In one case, a 29-year-old woman called the authorities on Jan. 12 and said she had gone to the emergency room at Mount Sinai on the Upper East Side for shoulder pain, where between midnight and 2 a.m. that day she was assaulted by Dr. Newman, the police said.

Nurses initially gave the woman pain pills and a morphine shot before taking her in for an X-ray, a law enforcement official said, speaking on the condition of anonymity to discuss a continuing investigation. Then Dr. Newman came into her room and gave the woman another shot of morphine, even after she told the doctor that she had already received one.