Many people with severe mental health problems miss out on the care they should receive for physical illnesses, researchers say.
A British Journal of Psychiatry paper found those with severe mental illness were less likely to get drugs for conditions such as high blood pressure.
The University of Leicester team reviewed 61 existing studies to reach their conclusions.
Campaigners said patients' physical health was "often overlooked".
The studies analysed by the team covered almost two million people, mainly living in the US.
They looked at treatment of conditions including cardiovascular disease, diabetes, cancer, arthritis, osteoporosis and HIV.
It was found that patients with severe mental illness, such as schizophrenia, received lower than expected prescriptions for essential drugs to treat high blood pressure, including ACE inhibitors, beta-blockers and statins.
Overall, it was estimated that the rate of undertreatment for medical conditions was 10% for those with severe mental illness.
'Not taken seriously'
Dr Alex Mitchell of the University of Leicester, who led the study, said: "People with severe mental illness appear to be receiving significantly less medication for medical disorders, particularly for cardiovascular problems."
He added: "Mental health professionals may not feel confident in prescribing medication to treat physical problems, and hospital specialists may be worried about interactions of mental health medication.
"However we cannot rule out the possibility that medical conditions are being undertreated where they co-exist with mental health problems."
Paul Jenkins, chief executive of the charity Rethink Mental Illness said: "The report is absolutely right to call for clinicians to prioritise the physical health of people with severe mental illness.
"It is a scandal that this group of people die on average 20 years younger than the general population, mostly due to preventable physical conditions.
"Too often mental health professionals overlook the physical health needs of their patients.
"At the same time, busy professionals don't always monitor the side effects from antipsychotic medication properly.
"Many of our members say that they are not taken seriously by doctors when they raise concerns about their physical health.
"But it doesn't have to be this way - there are simple steps that mental health professionals can take to help their patients stay physically healthy."