Only 12 per cent of the homeless adults in Vancouver participating in a Simon Fraser University study, who had been diagnosed with a severe mental illness, took their antipsychotic medication at or above the level needed to be effective.
And the researcher who led the study said it shows the need for more frequent contact between the individuals and primary health-care providers.
The study examined 290 homeless persons who were diagnosed with a severe mental illness over a 15-year period – the vast majority had schizophrenia, while others had bipolar disorder.
Stefanie Rezansoff, a health-sciences researcher at the university and a PhD candidate, said the study found the level of adherence to antipsychotic medication among the participants was very low.
"Guidelines generally indicate that if a person is taking their medication 80 per cent of the time, that that is considered therapeutically acceptable," she said in an interview. "We found in our study that only 12 per cent of people actually meet that 80-per-cent threshold."
Ms. Rezansoff said the study, which was recently published in the journal Social Psychiatry and Psychiatric Epidemiology, is the first to look at the use of antipsychotic medication among homeless persons over an extended period. She said adherence to antipsychotic medication can be low whether a person is homeless or not, but it was particularly low among study participants.
"One of the reasons … is due to the general chaos that tends to be associated with being homeless," she said.
"You have nowhere to store medication, it gets frequently stolen from you, you don't have regular meal times. All of these things that define homelessness make it very difficult to adhere to an antipsychotic regimen."
Ms. Rezansoff said one potential solution is greater engagement between study participants and primary health-care providers. She said finding a GP can be a challenge, whether a person is homeless or not.
Another potential solution, Ms. Rezansoff said, is the use of long-acting injectable medication. She said most of the people who are prescribed antipsychotic medication receive daily tablets. Injections, she said, can work for several weeks.
Vancouver Coastal Health, which provides health-care services in the region, said in a statement that it "welcomes the results of any study that contributes to a greater understanding of this client group.
"Our homeless clients are a challenging population to serve and many have complex health problems. We have been adjusting our services to improve care to this client group to better meet their health-care needs," the statement read.
Vancouver Coastal said its Downtown Eastside second-generation strategy addresses some of the challenges of reaching homeless clients.
It said its new mental-health and substance-use drop-in centre better connects vulnerable clients with health-care services and a new multidisciplinary case-management team treats complex-care adults.
Vancouver Coastal said its community treatment teams actively reach out to clients, including those who are homeless.
A B.C. Ministry of Health spokesperson said community treatment teams have been established in various B.C. health authorities, though the ministry recognizes there is more work to be done.