The crash occurred yesterday.
A driver was arrested yesterday for failing a drugs test after a three-car crash.
Police attended the crash on Old Dalkeith Road yesterday morning.
One of the drivers tested positive on a drugwipe for cannabis and cocaine, and was arrested.
A blood sample was taken for analysis.
Police officers used new drug testing kits which were brought into use across Scotland in October.
The crash occurred on Old Dalkeith Road.
The roadside kit uses a mouth swab, and a blue line appears if the person tested is over the prescribed limit for cannabis or cocaine.
The limit is as close to zero as possible, and is in place in case of accidental exposure such as walking near another person smoking cannabis.