Quetiapine
Quetiapine is an atypical antipsychotic that blocks dopamine and serotonin receptors, and its strong antihistamine action accounts for the sedation seen at lower doses. In practice it is prescribed for depression, for anxiety, and for insomnia, often as an add-on rather than as a first choice. It is prescription-only.
It is usually taken at bedtime, with or without food, because drowsiness is the most predictable effect and can carry over into the next morning. Over longer use it can change body weight, raise blood glucose and shift cholesterol and triglycerides, which is why glucose, HbA1c and the lipid panel are checked periodically rather than once. It can also prolong the QT interval, so it matters that a doctor knows about every other medicine being taken, particularly other drugs that affect heart rhythm.
Fainting, palpitations or an irregular heartbeat need medical attention promptly, as do heavy thirst, frequent urination or rapid weight change. Sedation that does not fade, or worsening mood, is also a reason to see a doctor rather than adjust the drug alone.
Reference information, not medical advice. Discuss any change with your doctor.