Life has its ups and downs and everyone gets sad once in a while, but the toll of mental illness can be grave. The numbers reveal that one in ten people in the US takes antidepressants and the nationwide rate of antidepressant use has quadrupled in the last 30 years. In most cases, these drugs help stabilize mood without any serious drawbacks. But adverse reactions can happen, as on display in the new thriller Side Effects, out this Friday in theaters across North America, written by Scott Burns and directed by Steven Soderbergh, the same person behind the 2011 viral pandemic movie Contagion. Both films are structured around a specific modern-day fear—but the threat in Side Effects mutates faster than any virus could.