The overall narrative of The Silent Patient and many of the characters’ individual narratives demonstrate the dangers of unresolved or improperly treated mental illness. Alicia clearly never resolved the trauma of Vernon’s destructive comment that psychologically “killed” her; Theo’s assault on Alicia and Gabriel was thus able to reawaken this trauma, with deadly results. Theo likewise has unresolved issues related to his abusive upbringing, which make his unhealthy attachment to Kathy so strong that he can’t leave her after discovering her adultery—again, with harmful results to himself and others. Then there is Alicia’s mother, Eva, who presumably struggled with mental health issues that led to her suicide (and/or Alicia’s attempted murder—the novel never makes her intent clear) and Theo’s father, whom he believes had an undiagnosed personality disorder.

The novel’s setting of The Grove medical facility and Theo’s profession highlights the theme repeatedly, as even secondary characters exhibit struggles with mental health issues. The violent patient Elif, for instance—but also the nurse Yuri—describes a history of troubling stalking behavior to Theo. By depicting characters at both ends of the spectrum (patient versus caregiver/doctor/nurse) with mental health issues, the novel makes it clear just how universal these problems are.