The 20-year old is in a critical condition at the Royal Infirmary in Edinburgh after the crash on the A883 Denny-Falkirk Road on Sunday evening.
A front seat passenger, a 33-year-old man, sustained serious, but not life threatening injuries, and was taken to the Queen Elizabeth University Hospital in Glasgow where his condition is described as serious but stable.
A 28-year-old woman - the rear seat passenger - sustained minor injuries and was treated at Forth Valley Royal Hospital.
The crash happened around 7.40pm when a white Vauxhall Corsa travelling east left the road near Headswood Mill Farm.
Emergency services attended, and the road was closed.
It re-opened around 1:00am on Monday.
Sergeant David Ross said: “We are keen to speak to anyone who may have seen what happened and also anyone with dash-cam that could assist with our investigation."Call 101, quoting incident number 2935 of Sunday, February 13.