“Treatments affect people. And if you can affect people, you can’t be 100% confident what those effects are going to be,” Crawford told Quartz. “There’s an idea out there that psychological therapy is only helpful. But we think that patients who make choices about engaging in psychological therapy should be given information at the start, which is most people are going to benefit from an intervention, but some people may not.”

The researchers found that ethnic minorities and non-heterosexuals were more likely to experience lasting bad effects, though there’s no clear data on why that might be. Previous research has found that the positive effects of therapy are just as strong for ethnic minorities as for Caucasians. However, Crawford speculates that minority groups might be more likely to be misunderstood.

“In order to engage in a healthy and helpful therapeutic relationship, the therapist needs to understand the social and cultural context of the patient’s life,” he says. “For some who have experience of being marginalized, the experience of being offered help may not be inherently helpful.”