Thirty to 50 percent of depressed people aren’t helped by SSRI antidepressants, and researchers may have discovered why.

In a recent study, researchers including Silvia Poggini from Istituto Superiore di Sanità, Rome, conducted experiments on mice to determine if environments had an effect on their stress levels, a news release from the European College of Neuropsychopharmacology (ECNP) stated.

A group of 24 mice were stressed for two weeks and then treated with the SSRI fluoxetine. Half of the mice were then placed in a comfortable environment while the other half were stressed just as they were before. After measuring the stress-related cytokine levels in the brain, the results found mice placed in a comfortable environment showed an increase of pro-inflammatory cytokines while the stressed mice presented an increase of anti-inflammatory cytokines and more symptoms of depression, a sign that taking an antidepressant alone is not a complete treatment for depression.

“This may mean that we have to consider how we can adapt our circumstances, and that antidepressant treatment would only be one tool to use against depression,” Poggini said in a news release.

“In a certain way it seems that the SSRIs open the brain to being moved from a fixed state of unhappiness, to a condition where other circumstances can determine whether or not you recover,” she said.

Despite the results from the experiment, Poggini warns sufferers of depression about applying it to their own lives.

“Our results are preliminary and we strongly recommend that patients stick to the treatment prescribed by their doctors,” Poggini said in the release.

An SSRI functions by increasing the serotonin levels in the brain, but this simply allows the brain to enter a phase with the potential to change rather than actually changing, the release noted.

Read more: Experimental Antidepressant Drug Targets Same Enzyme Behind Inflammatory Diseases

Alboni S, Poggini S, Garofalo S, Milior G, El Hajj H, Lecours C,Girard I, Gagnon S, Boiskoly-Villeneuve S, Brunello N, Wolfer D, Limatola C, Tremblay M, Maggi L, Branchi I. Fluoxetine treatment affects the inflammatory response and microglial function according to the quality of the living environment. Brain, Behaviour, and Immunity. 2016