Siblings are often the forgotten family members when it comes to offering support to relatives of people suffering from mental illnesses, a Victorian researcher says.

La Trobe University lecturer Siann Bowman said her study of 157 siblings of young people suffering from early psychosis showed they were affected by the illness of their sibling.

The young people were worried about their sibling's suicide attempts, violent incidents and whether the mental health problem would improve, Ms Bowman said.

A suicide attempt, involuntary hospital admission or violence at home reduced the satisfaction siblings felt about their quality of life, she said.

Younger siblings felt more traumatised than older siblings, who may be more likely to move out if things got tough at home, Ms Bowman said.