Seroquel (quetiapine) causes drowsiness in a large proportion of people who take it, and this is often the first and most noticeable side effect. Beyond sedation, the drug carries meaningful risks for metabolism, heart rhythm, and movement disorders that vary depending on dose and how long you take it. Here’s what to expect and what to watch for.
Drowsiness and Early Side Effects
Sleepiness is the most widely reported side effect, and it hits hardest during the first few days. The initial dose-titration period, typically days three through five, is when somnolence peaks. Quetiapine reaches its highest concentration in your blood about 1.5 hours after you swallow a dose, which is why most people take it at bedtime. Dizziness when standing up quickly, confusion, chills, and cold sweats are also common in the early weeks. Many of these effects ease as your body adjusts, though some degree of sedation can persist for as long as you’re on the medication.
Weight Gain and Metabolic Changes
Quetiapine belongs to a group of atypical antipsychotics known to interfere with how your body processes sugar and fat. The metabolic picture includes several overlapping problems: weight gain, rising blood sugar (sometimes progressing to new-onset diabetes), increased cholesterol and triglycerides, and a higher long-term risk of cardiovascular disease. Among the atypical antipsychotics, quetiapine is considered to carry a relatively higher metabolic risk, in the same tier as olanzapine and clozapine.
Weight gain isn’t guaranteed, but it’s common enough that your prescriber will likely order periodic blood work to check fasting glucose and lipid levels. The changes can develop gradually, so they’re easy to miss without lab monitoring. If you notice your clothes fitting differently or increased thirst and urination, those are worth reporting.
Movement Disorders
Antipsychotics work by blocking certain brain receptors involved in movement control, which is why they can cause involuntary movements or muscle stiffness. These are called extrapyramidal symptoms, and they range from mild restlessness and tremor to more rigid, Parkinson’s-like movements. Quetiapine generally causes fewer movement problems than older antipsychotics, but the risk isn’t zero.
The more concerning movement disorder is tardive dyskinesia: repetitive, involuntary motions of the face, tongue, or limbs that can become permanent. A large study of over 164,000 antipsychotic users in the U.S. found an annual prevalence of tardive dyskinesia between 0.8% and 1.9%, and roughly 80% of those cases involved people taking atypical antipsychotics like quetiapine. The risk increases with longer use and higher doses. If you notice lip smacking, tongue darting, or unusual facial movements, bring them up immediately, as early detection makes reversal more likely.
Heart Rhythm Concerns
Quetiapine can lengthen a specific electrical interval in your heartbeat called the QT interval. When this interval stretches too far, it raises the chance of dangerous heart rhythm problems. In a study published in Heart Rhythm Journal, about 13% of quetiapine users developed severe QT prolongation. Among those who did, the odds of life-threatening ventricular arrhythmias were nearly three times higher, and the odds of sudden cardiac death were roughly 2.3 times higher compared to those without QT changes.
Several factors increase your vulnerability: heart failure, low potassium levels, older age, and certain other medications (particularly heart rhythm drugs). If you have a pre-existing heart condition, your prescriber may order an electrocardiogram before starting treatment and periodically afterward.
Risks for Older Adults With Dementia
Seroquel carries an FDA boxed warning, the most serious type, for elderly patients with dementia-related psychosis. In an analysis of 17 placebo-controlled trials lasting about 10 weeks each, patients taking atypical antipsychotics had a death rate of approximately 4.5%, compared to 2.6% for those on placebo. That translates to a 1.6 to 1.7 times greater risk of death, with most deaths stemming from cardiovascular events (heart failure, sudden death) or infections like pneumonia. Seroquel is not approved for treating dementia-related psychosis.
Eye Health
Early in quetiapine’s history, there was concern that it might cause cataracts, and prescribing guidelines once called for eye exams every six months. That requirement has since been relaxed. The World Health Organization considers cataract formation from quetiapine “unlikely,” and routine eye exams are now considered sufficient. That said, people with other risk factors for cataracts, such as diabetes or long-term steroid use, should keep up with regular eye checkups.
Withdrawal and Discontinuation
Stopping quetiapine abruptly can trigger a withdrawal syndrome. Reported symptoms include nausea, vomiting, dizziness, headache, anxiety, rapid heart rate, sweating, and lightheadedness upon standing. These symptoms can appear within days of stopping and, in some cases, prove difficult to manage even with a slow taper. One documented case attempted reductions as small as 12.5 mg every five days and still encountered significant withdrawal effects.
If you and your prescriber decide to discontinue Seroquel, a gradual dose reduction is the standard approach. There’s no single universally agreed-upon tapering schedule, so the pace will depend on your dose, how long you’ve been taking it, and how you respond to each reduction. The key point: don’t stop on your own. Withdrawal is real, and a planned taper makes it far more manageable.
Low Dose vs. High Dose
Quetiapine is prescribed across a wide dosage range. At low doses (25 to 100 mg), it’s frequently used off-label for insomnia and anxiety, where sedation is essentially the intended effect. At higher doses (300 to 800 mg), it’s used for schizophrenia and bipolar disorder, and that’s where the full spectrum of side effects becomes more relevant. Movement disorders, metabolic changes, and cardiac effects are all more likely at higher doses and with longer treatment duration. Even at low doses, though, metabolic monitoring is reasonable if you’re taking the medication for months or years.