Veronika is a 24-year-old Slovenian woman working at a library. Despite being well-educated and socially successful, she feels a profound apathy toward her routine and a lack of meaning in the world. After a suicide attempt, she awakens in the Villete psychiatric hospital, where she is told her heart is fatally weakened and she has only days to live.

Dr. Igor is the head doctor at the Villete psychiatric hospital. He formulates an unethical medical theory about a substance he calls "Vitriol" or "bitterness," which he believes is caused by social conformity and a disconnection from life. He orchestrates a drastic psychological experiment on Veronika by lying to her about a terminal heart condition.

Eduard is a Slovenian man in his twenties residing at Villete with a diagnosis of schizophrenia. The son of a Yugoslavian ambassador, he previously lived in Brazil where he discovered a passion for painting and alternative subcultures. The intense pressure from his family to conform to a respectable diplomatic career severely impacted his mental stability.

Zedka is a patient at Villete receiving treatment for chronic depression. Prior to her institutionalization, she lived a conventionally successful life as a married woman with children, but secretly obsessed over an "Impossible Love" from her past. She introduces Veronika to the complex social dynamics of the hospital.

Mari is a former lawyer in her mid-forties who suffers from severe panic attacks. She initially entered Villete for temporary relief but chose to stay permanently after facing stigma from her law firm and husband. As a core member of the Fraternity, she prefers the predictability of the hospital to the pressures of the outside world.

Paulo Coelho writes himself into the narrative as a writer who hears about Veronika's experience. Reflecting on his own adolescent years spent in mental health institutions, he uses Veronika's journey to process and write about the divide between societal conformity and authentic living.

Veronika's mother is a middle-class woman who doted on her daughter and ensured she received a thorough education. She strongly discouraged Veronika from pursuing music, viewing piano playing merely as a tool to attract a respectable husband.

Eduard's father is a Yugoslavian ambassador who expects his son to follow in his political footsteps. Horrified by Eduard's artistic interests and alternative lifestyle, he demands his son abandon painting and face reality, leading to Eduard's eventual institutionalization.

She is the daughter of the head doctor at Villete. She shares the story of her namesake's experiences at the hospital with the author, setting the novel's events in motion.

Maria is a Brazilian girl who heavily influences Eduard during his teenage years. Her deep interest in new-age occultism exposes Eduard to alternative ways of thinking that contrast sharply with his upper-class upbringing.