Researchers analysed 18 prisons in depth
Healthcare in prisons in England is still not good enough - despite a shake-up of the system in recent years, two leading watchdogs say.
The NHS has only recently taken control of services, but already the Healthcare Commission and the Chief Inspector of Prisons have said more must be done.
Their report highlighted poor training and assessment of prisoner needs.
The government agreed there was a need for improvement, but said money was being invested.
The 152 primary care trusts in England have responsibility for providing a broad range of services in prison, including GP care, dentistry, mental health services and eye and foot care.
This is done through either running in-house clinics or by sending health staff into prisons at set times.
Prison healthcare was handed over to the health service primarily to help create NHS quality of care for inmates.
The watchdogs, whose report is based on in-depth inspections of 18 prisons, said it was hard to establish whether this was yet the case as half of services did not measure performance against NHS standards.
The report also highlighted the fact that only in four cases had need assessments been carried out, while 13 of the services did not have systems in place to divert those with severe mental health problems to secure health units.
The inspectors said the way training for staff was run needed to be improved, while consultation with the prison population about what they thought of services should be a top priority.
However, they did praise health promotion, saying prisoners were given good support to help them quit smoking as well as advice on sexual health and healthy eating.
The way drugs were prescribed and distributed was also commended.
Anna Walker, the Healthcare Commission's chief executive, said: "It is clear from our work that, while improvements have been made, healthcare for offenders is not what it should be. This must change."
Juliet Lyon, director of the Prison Reform Trust, said there needed to be a two-fold approach to improve services for a "vulnerable and unhealthy population".
"Services are probably better than they were, but to get to the right standard staff must consult with prisoners and find out what they need.
"We also need to see offenders engage with health service before they reach prison. Many come into contact with the police with drug addictions or mental health problems and they should be signposted to services then."
Care services minister Phil Hope admitted services needed to improve, but added investment was increasing.
"Offenders, including those with mental illness, must receive the healthcare treatment they need."
Meanwhile, a separate joint report by the Healthcare Commission and Probation Inspectorate criticised the approach taken by youth offending teams to health.
It said there was a lack of information sharing between the teams and NHS professionals which meant young offenders missed out on treatment.