I agree with Claire Laurent that the term 'dual diagnosis' is unhelpful in describing people with mental illness and substance misuse ('Altered image', news focus, page 18, 14 September), and am pleased to inform her that its use is already on the decline.

The issues around so-called dual diagnosis are complicated, and homeless people with mental health problems are by no means a homogeneous group. The important thing for those commissioning or delivering services is that substance misuse is just one of a list of potential complicating factors which adds another complexity to a person's situation.

In deciding whether an individual with complex needs should receive a specialist mental health service, the primary issue is whether that person is suffering from severe and enduring mental illness. It is unacceptable for mental health services to turn people away on the basis that the underlying cause of their illness is substance misuse. This implies they are responsible for the illness and so unworthy of treatment. And of course, the underlying reasons why people misuse substances often extend to circumstances well out of the individual's control.

Most homeless people present with a wide range of needs - substance misuse, poor physical health, contact with the criminal justice system, lack of support and poor daily living skills to name a few.

Many suffer from mild to moderate mental illness, but at the level which can appropriately be managed by primary care. Referral to specialist mental health services is often based on complexity of need rather than severity of mental illness. That, and the fact that an appropriate service does not exist. An intensive support service for those with complex needs but not severe and enduring mental illness is needed. But this should not be located in secondary care. Users of mental health services still experience stigma, and we should not push people into them indiscriminately.

Cath Laverty Homeless mental health service Central Manchester Healthcare trust