James Battrick, 21, from Cadnam, admitted two counts of driving without due care while under the influence of drugs.
Lily Butterfield-Godwin and Abbey Rogers, both 19, from Lyndhurst, died on 13 December in the New Forest crash.
Both women were born on the same day and died at the scene at midnight.
The crash happened in Gosport Lane, Lyndhurst, next to the entrance to Vernalls Farm.
The car Battrick was driving, a Mazda RX8, left the road, crashed against a wall and ended up head-on with a brick gate pillar.
After the sentence, police said Battrick had consumed a minimum of five pints of cider in the hours before the crash and his blood showed a high level of cannabis.
Police found that the car headlights had been switched off.
The vehicle was discovered by local residents who had heard a loud noise.
Robin Butterfield, Lily's grandfather, said: "One year or 20, it makes no difference to us.
"I feel in a strange way sorry for his family and for him.
"He was just a silly young lad."
Sergeant Adrienne Jerram, senior investigating officer for Operation Marne, said: "Lily and Abbey were friends who were born and died on the same day. This collision was a terrible tragedy caused by the mindless actions of a young driver who should never have got behind the wheel that night.
"If Battrick hadn't been drinking, or smoking cannabis that day, there is every chance that Lily and Abbey would still be with us."
Battrick was sentenced at Bournemouth Crown Court. During a previous hearing he also admitted possession of cannabis.
A driver who caused the deaths of two passengers while under the influence of drugs has been jailed for six years and nine months.