The incident, involving two HGV lorries, took place around 10.10am on Thursday (August 26).
Part of the A1 will remain closed until Bitumen, spilled on the road during the collision, is cleared.
A Police Scotland spokesperson said: “Officers were called around 10.10 am to reports of a crash on the A1 near Thorntonloch involving two HGVs.
“A 22-year-old man has been taken to the Edinburgh Royal Infirmary for treatment.
“As a result of the incident, Bitumen has spilled onto the road, and it will remain closed until the vehicles have been removed and the road has been cleared.”