Kennedy, 54, the daughter of former U.S. Senator Robert Kennedy and ex-wide of New York Gov. Andrew Cuomo, allegedly took the sleep medication Ambien in 2012 before driving and crashing her car into a tractor trailer. She is charged with driving while impaired by drugs.
She was accompanied to court by her mother Ethel, 85, confined to a wheelchair, and her brother Douglas, the New York Daily News reported.
In an opening statement Monday her lawyer, Gerald Lefcourt, said the medication "hijacked" Kennedy's decision-making that morning, adding, "This is not someone who was on some party drug."
Prosecutors said it hardly mattered, Assistant District Attorney Stefanie DeNise saying of Kennedy, "Her actions and decisions she made that day would result in her arrest."
The trial, before a six-person jury, is expected to last a week. Although Kennedy has no criminal record, she could be sentenced to a year in prison if convicted, the White Plains Journal reported.