The state says Lincoln was impaired by the drugs - and also distracted. It intends to prove she was swerving on the road before hitting and killing Steven Covert on Van Giesen Street.
The defense plans to argue the 33-year-old had taken her prescription for years and never had an issue behind the wheel.
Prosecutor Terry Bloor said, "She drifted out of the turn lane and then she drifted into oncoming traffic."
Defense attorney Scott Thompson said, "Natalie had reported no issues with driving as a result of being on the Baclofen for over three years."
Covert's son was the first to take the stand today. He was riding with his father when the 50-year-old was killed near West Richland.