When depression hits, finding the right treatment as soon as possible is crucial.

For many patients, treating depression includes taking an antidepressant medication to help them recover. But certain types of antidepressants are just not helpful for some patients. Doctors don’t understand why this is, and they often don’t know in advance who will or won’t benefit from a particular drug. Finding the right antidepressant for a particular patient, therefore, often requires repeat trials of different medications. But trying out medication takes time, money and patience.

Scientists writing in the International Journal of Neuropsychopharmacology are working on a method that gives insight into patients’ likely responsiveness to specific medications. As shown in a small study by Canadian and European researchers, getting the answer doesn’t even require a patient to actually take the medication in question.

The process uses a blood sample and measures biomarkers, such as specific chemical signs of inflammation. The researchers say people whose inflammation reaches a certain threshold may not respond to some antidepressants alone. That doesn’t mean that antidepressants won’t work at all in people with higher levels of inflammation. Instead, it indicates that a combination of antidepressants and anti-inflammatory medications may work best.

On the other hand, a lower inflammation level below the cut-off point points to what the researchers call a “less aggressive” depression where an antidepressant probably will be helpful. In the future, the blood test results may guide doctors in prescribing medications for patients to try. More research and trials need to be done, but the blood test raises the possibility that, one day, finding the best antidepressant might get easier. For those who struggle through the darkness of depression, this is welcome news.