Veronica Saeler, 37, of Oakland Township was arrested for drugged driving in Oakland Township.
Police said they initially stopped her for going 10 miles over the 35 mph speed limit.
Saeler denied that she had been drinking or using drugs.
But after failing a field sobriety testing, according to court documents, she admitted to smoking marijuana earlier that day.
She was later taken to Butler Memorial Hospital for a blood test.
Saeler was arraigned on charges of driving under the influence of a controlled substance, speeding and careless driving.
She was placed in the Butler County Prison on $2,500 bail following arraignment.