[18] The drug is typically indicated to have superior efficacy over other existing antipsychotics for the treatment of bipolar disorder, followed by olanzapine and aripiprazole, in that order.

Quetiapine is currently the only antipsychotic to produce equal efficacy as a standalone therapy for mixed manic-depressive mood swings as it is when used in combination with an SSRI antidepressant.

However, quetiapine is less potent than clozapine, amisulpride, olanzapine, risperidone, and paliperidone, respectively, in alleviating psychotic symptoms or treating schizophrenia.

[22] There is tentative evidence of the benefit of quetiapine versus placebo in schizophrenia; however, definitive conclusions are not possible due to the high rate of attrition in trials (greater than 50%) and the lack of data on economic outcomes, social functioning, or quality of life.

[30] The use of low doses of quetiapine for insomnia, while common, is not recommended; there is little evidence of benefit and concerns regarding adverse effects.

[31][32][33][34][35][36] A 2022 network meta-analysis of 154 double-blind, randomized controlled trials of drug therapies vs. placebo for insomnia in adults found that quetiapine did not demonstrate any short-term benefits in sleep quality.

[39][40] These safety concerns at low doses are corroborated by Danish observational studies that showed use of specifically low-dose quetiapine (prescriptions filled for tablet strengths >50 mg were excluded) was associated with an increased risk of major cardiovascular events as compared to use of Z-drugs, with most of the risk being driven by cardiovascular death.

[41] Laboratory data from an unpublished analysis of the same cohort also support the lack of dose-dependency of metabolic side effects, as new use of low-dose quetiapine was associated with a risk of increased fasting triglycerides at 1-year follow-up.

[42] It is sometimes used off-label, often as an augmentation agent, to treat conditions such as Tourette syndrome,[43] musical hallucinations[44] and anxiety disorders.

[45] Quetiapine and clozapine are the most widely used medications for the treatment of Parkinson's disease psychosis due to their relatively low extrapyramidal side-effect liability.

[48] The evidence is insufficient to rule out any risk to the foetus but available data suggests it is unlikely to result in any major foetal malformations.

[58][59][60][61][62] Most instances of acute overdosage result in only sedation, hypotension and tachycardia, but cardiac arrhythmia, coma and death have occurred in adults.

Serum or plasma quetiapine concentrations are usually in the 1–10 mg/L range in overdose survivors, while postmortem blood levels of 10–25 mg/L are generally observed in fatal cases.

[20][82][83] Quetiapine has fewer extrapyramidal side effects and is less likely to cause hyperprolactinemia when compared to other drugs used to treat schizophrenia, so is used as a first line treatment.

[87] AstraZeneca submitted a new drug application for a sustained-release version of quetiapine in the United States, Canada, and the European Union in the second half of 2006 for treatment of schizophrenia.

In December 2008, Biovail announced that the FDA had accepted the company's ANDA to market its own version of sustained-release quetiapine.

In December 2008, AstraZeneca notified shareholders that the FDA had asked for additional information on the company's application to expand the use of sustained-release quetiapine for treatment of depression.

[100] In April 2010, the U. S. Department of Justice fined AstraZeneca $520 million for the company's aggressive marketing of Seroquel for off-label uses.

[101][102][103][104] Approximately 10,000[105] lawsuits[106] have been filed against AstraZeneca, alleging that quetiapine caused problems ranging from slurred speech and chronic insomnia to deaths.

[107] A group of University of Minnesota bioethicists charged that the trial involved an alarming number of ethical violations.

[108] In August 2011, the UK's Medicines and Healthcare products Regulatory Agency (MHRA) issued a class-4 drug alert following reports that some batches of Nurofen plus contained Seroquel XL tablets instead.

[109] Following the issue of the Class-4 Drug Alert, Reckitt Benckiser (UK) Ltd received further reports of rogue blister strips in cartons of two additional batches of Nurofen Plus tablets.

Following discussions with the MHRA's Defective Medicines Report Centre (DMRC), Reckitt Benckiser (UK) Ltd decided to recall all remaining unexpired stock of Nurofen Plus tablets in any pack size, leading to a Class-1 Drug Alert.