The female motorist, 38, and her passenger were left trapped in a Ford Focus after it crashed on the A41 outside Dovecote Bletchley Court, near Market Drayton.
The seriously-injured passenger was trapped for more than an hour and a half after the car overturned about 4.10am on Monday.
The two women were freed by fire crews before being rushed to the major trauma centre at Royal Stoke University Hospital.
The driver, from Stafford, has since been released from hospital and arrested but the passenger remained in hospital on Monday afternoon.
She was seriously injured but in a stable condition, West Mercia Police said as officers appealed for witnesses to come forward.
A spokeswoman for the force said: "A blue Ford Focus was heading towards Market Drayton when it left the road and overturned.
"The driver, a 38-year-old woman from Stafford, was initially taken to hospital for treatment but has since been arrested on suspicion of driving whilst under the influence of drugs.
"A passenger, a woman in her thirties, also suffered serious injuries and remains in Royal Stoke Hospital in a stable condition.
"Anyone with information or dash-cam footage is urged to contact 101 quoting reference 00045i of 8 January, or alternatively information can be reported online through the Tell Us About section of our website."
West Midlands Ambulance Service sent two ambulances and a paramedic officer to the incident. A Merit trauma doctor and critical care paramedic were also sent to the scene.
Police officers were also on scene to close the road in both directions and help make the area safe.
Shropshire Fire & Rescue Service sent four appliances from Hodnet, Market Drayton and Wellington.
A WMAS spokesman said: "On arrival, ambulance staff found a car that had rolled over but had ended up on its wheels.
“The front-seat passenger was trapped so they immediately requested the fire service to be responded.
“The woman was trapped for a little over half an hour while ambulance staff worked with firefighters to extricate her.
“The woman had suffered multiple injuries. After treatment at the scene, she was taken on blue lights to the major trauma centre at Royal Stoke University Hospital where medics were awaiting her arrival.
“The driver, also a woman, had suffered less serious injuries but due to the level of damage to the car, was also taken to the same major trauma centre as a precaution.”