There’s no pill to cure a concussion. If a hard blow caused a person’s brain to knock against his skull, only rest can help him heal—if a patient goes back to her usual activities before she has fully recovered, she can cause permanent damage to her brain. But the length of that convalescence period can vary a lot, due to factors like the severity of the concussion or the consumption of alcohol and drugs. Now a team of researchers has found that if a patient has physiological effects of mental illness–like muscle soreness associated with depression–before the concussion, that can help determine the rate of recovery, according to a study published last week in the journal Neurology.

The researchers were looking at somatic symptoms, physical aches and pains caused by psychological distress, that were present before the concussion occurred. They surveyed over 2,000 high school and college athletes to determine their somatic symptoms when they didn’t have concussions. 127 of those athletes ended up getting concussions during the sports season (about 60 percent of those concussions were from football), and researchers predicted how long their recovery would take based on information like their demographics, the severity of their injury, and if they have a history of concussions, along with their somatic condition.

Patients that had somatic symptoms before the concussion took longer to recover than those who had no such symptoms, the researchers found. It took 20 days for 80 percent of people with symptoms to recover, while it only took 10 days for 80 percent of patients without symptoms. The severity of the post-concussion symptoms was also correlated with longer recovery time, though the study wasn’t designed to reveal how a specific cause influenced the length of convalescence.

In this study, too, there’s no way to rule out the effect of placebo. If patients think they are less well—either as a result of the concussion or even before it—they may well take longer to recover than patients with outcomes buoyed by placebo.

Scientists have known for a while that mental illness, such as anxiety and depression, can affect the duration of concussion symptoms. So, too, can a concussion precipitate the onset of mental illness, in some cases increasing a patient’s likelihood of developing a disorder by about 400 percent. And though there’s a strong correlation between psychiatric disorders and mild brain trauma like a concussion, scientists still aren’t sure of the mechanism that links them.

While this study doesn’t illuminate the mechanisms at play, the findings could help ensure that patients with concussions take all the recovery time they need so that they don’t cause permanent brain damage. The researchers hope that future studies will be able to uncover earlier interventions for people with concussions to improve their long-term neurological health.