More sniffer dogs are being used at a juvenile custody centre in north Staffordshire because of concerns about cannabis being smuggled in.
A report by the Board Of Volunteers at Werrington Young Offenders Institution states that the drug could be the cause of more bullying amongst inmates.
Conditions in the Denby Unit are also criticised. In summer, temperatures in cells can reach more than 30C (86F).
The institution's governor denied there is a problem with violence or drugs.
Frank Flynn said: "I am incredibly concerned with the misuse of drugs within any institution but with our particular population, substance misuse - although you are highlighting it - is not the huge issue that people would normally think."
The report said cannabis is most likely to be brought in to Werrington through visits and when inmates are released for work experience.
But it adds that the situation has got better in the last few months.
Also, a new healthcare scheme has been introduced and there is an increase in the number of evening classes.
The board of volunteers is appointed by the government and visits the centre every week.