A teenager who stabbed his grandmother to death and seriously injured his grandfather as they lay in bed will claim he was suffering a psychotic episode at the time due to his use of the drug M-Cat, a prosecutor has told a jury.
Hull Crown Court was told there was no dispute that Lewis Dale, 17, killed Irene Dale, 78, and seriously injured her husband Allan, 80, with a kitchen knife.
Adrian Strong, prosecuting, described how Dale attacked his grandparents as they were in bed at their home in Summergangs Road, in Hull, in April.
Mr Strong said Dale was a user of the drug mephedrone which he said was also known as "meow meow or M-Cat".
He said: "I anticipate that Lewis Dale will tell you that at the time of the attack on his grandparents he was suffering a psychotic episode as a result of his drug use."
Mr Strong said mephedrone used to be called a "legal high" but was outlawed in 2010 and is now a class B controlled drug.
He said users claim it provokes euphoria and heightened energy.
But he said there were also reports it caused restlessness, anxiety, confusion and psychosis.