Many mental illnesses are as bad for you as smoking, research has suggested.
Life expectancy for people with mental health problems is less than for heavy smokers, experts have found.
Serious mental illness can reduce a person's life expectancy by 10 to 20 years, when the average reduction in life expectancy for heavy smokers is eight to 10 years, according to researchers from Oxford University.
But mental health has not been the same public health priority as smoking, they said.
The study, published in the journal World Psychiatry, analysed previous research on mortality risk for a whole range of problems - mental health issues, drug and alcohol abuse, dementia, autistic spectrum disorders, learning disability and childhood behavioural disorders.
The authors examined 20 papers looking at 1.7 million people and over 250,000 deaths.
They found that the average reduction in life expectancy for people with bipolar disorder was between nine and 20 years, it was 10 to 20 years for schizophrenia, between nine and 24 years for drug and alcohol abuse, and around seven to 11 years for recurrent depression.
The loss of years among heavy smokers was eight to 10 years.
"We found that many mental health diagnoses are associated with a drop in life expectancy as great as that associated with smoking 20 or more cigarettes a day," Dr Seena Fazel of the Department of Psychiatry at Oxford University said.
"There are likely to be many reasons for this.
"High-risk behaviours are common in psychiatric patients, especially drug and alcohol abuse, and they are more likely to die by suicide.
"The stigma surrounding mental health may mean people aren't treated as well for physical health problems when they do see a doctor.
"Many causes of mental health problems also have physical consequences and mental illness worsen the prognosis of a range of physical illnesses, especially heart disease, diabetes and cancer.
"Unfortunately, people with serious mental illnesses may not access healthcare effectively.
"All of this can be changed.
"There are effective drug and psychological treatments for mental health problems.
"We can improve mental health and social care provision.
"That means making sure people have straightforward access to health care, and appropriate jobs and meaningful daytime activities.
"It'll be challenging, but it can be done.
"What we do need is for researchers, care providers and governments to make mental health a much higher priority for research and innovation.
"Smoking is recognised as a huge public health problem.
"There are effective ways to target smoking, and with political will and funding, rates of smoking-related deaths have started to decline.
"We now need a similar effort in mental health."
Dr John Williams, head of neuroscience and mental health at the Wellcome Trust, which funded the study, added: "People with mental health problems are among the most vulnerable in society.
"This work emphasises how crucial it is that they have access to appropriate healthcare and advice, which is not always the case.
"We now have strong evidence that mental illness is just as threatening to life expectancy as other public health threats such as smoking."
Mark Winstanley, chief executive of Rethink Mental Illness, said: "It's a scandal that people with mental illness are at risk of dying 20 years younger than average, because of preventable physical health problems.
"Our Lethal Discrimination report showed that more than 30,000 people with mental illness are dying needlessly every year - that's more than one avoidable death every 20 minutes.
"Signs of heart disease, diabetes and cancer are being missed because people aren't getting the right health checks.
"Obesity and smoking are also huge problems - 40% or all tobacco consumption is by people with mental illness, yet they aren't getting the support with lifestyle changes that other people expect and receive."
Care minister Norman Lamb said: " We've made it clear to NHS England that mental health needs must have equal priority with physical health.
"Public Health England has made exploring the link between mental health and life expectancy one of its key priorities."