Ilford GPs will provide healthcare for inmates in Chelmsford Prison.
The Partnership of East London Cooperatives (PELC), Ilford Hill, Ilford, has won a five-year contract to give "wellbeing services" and help improve the day-to-day quality of life at the jail in Springfield Park Hill.
The agreement will also cover the young offenders wing.
A PELC spokesman said prison staff have been tackling prisoners' use of drugs, which has been a cause of trouble within the prison. PELC will introduce policies for all doctors to not only monitor use of illicit substances but carefully monitor the use of prescribed medication.
The Ilford GPs will also be working closely with the resident psychiatrist to review prescribing for people with mental ill-health so that their medicines are always the most appropriate and effective.
"One of PELC's key focuses is creating a framework that ensures the healthcare services have a lasting effect," he added.
"It is currently running a full analysis to develop better communication with GPs to ensure prisoners get continuity of care and treatment after discharge."
A pool of six doctors will be available seven days a week to cover the shifts on a rotational basis.
Brian Jones, chief executive of PELC, said: "We are proud to contribute to the great work of the staff at HMP Chelmsford.
"Our approach to all healthcare is to put the patient and their wellbeing first, ensuring the vulnerable and those in need are not only cared for but equipped with the tools to look after themselves going forward - something we want to bring to Chelmsford Prison.
"It's also a new opportunity for our doctors to understand the continued needs of prisoners and the challenges presented.
"We were delighted to see so many GPs ask to work at Chelmsford. Considering the recent economic pressure the UK prison service has faced, PELC aims to provide an exceptional service whilst remaining cost-efficient."
Dr Ali Mohammed has started work there and said he found the work clinically interesting and challenging on a new level. "Working within a multidisciplinary team is energising and interesting," he said.
"Treating the patients with compassion and without judgement is providing me with the opportunity to understand the clinical issues being presented as a result of better patient communication."
Dr Omar Hashmi added: "The patients are friendly and there are really interesting cases that can involve internal as well as hospital referrals for ongoing management.
"I really enjoy using my clinical skills in the prison as a GP."
PELC is a not-for-profit social enterprise that serves more than two million people across east London and west Essex.
It was part of the "six-month turnaround" of King George's Hospital when its CQC rating increased by two gradings.
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