Nathan Blackett planned to return the Mercedes without anyone knowing he had taken it, South Tyneside Magistrates Court heard.
Paul Anderson, prosecuting, told the court the car keys had been put through the letterbox at the place he was living so that another person at the house could do some work on it.
He said: “That person was out for the day, so Mr Blackett decided to take the car to buy some heroin.
“No one would have been any the wiser but, as he was getting the drugs. someone got into the car and drove it away.
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“Mr Blackett called the police, and the car was later recovered undamaged.”
Blackett, 25, of Hexham Avenue, Hebburn, admitted taking a vehicle without the owner’s consent, driving without a licence, and driving without insurance.
The offences happened on June 6.
Chris Wilson, defending, said: “This was a short period of driving, less than three miles, and there’s no suggestion he did not drive responsibly,
“No one would have known what he had done had the car not been temporarily taken from him.
“Fortunately, it was recovered undamaged.”
He added: “Mr Blackett is far from a professional car thief.
“He is remorseful for his foolish actions that day.”
The magistrates adjourned sentence for the preparation of a probation report.
Blackett was bailed to return to court on November 8 to be dealt with.