Antipsychotics Diabetes Risk Peaks in First 90 Days, Study Finds

The antipsychotics diabetes connection is sharpest in the first three months of treatment, according to new research from University College London. Scientists analysed anonymous NHS GP records from nearly 97,000 adults in England who started taking a second-generation antipsychotic between 2000 and 2023, and found that blood sugar and weight climbed far faster in the weeks right after the first prescription than they had beforehand.

The study was published Oct. 14 in The Lancet Psychiatry and funded by the National Institute for Health and Care Research. It followed patients aged 18 to 59 with severe mental illness, drawing on records across a four-year window straddling the first prescription. The drugs studied were olanzapine, quetiapine, risperidone and aripiprazole, medicines widely prescribed for schizophrenia and bipolar disorder.

During the first 90 days, HbA1c, the blood marker that reflects average blood sugar, rose around fourteen times faster than it had before treatment began, while weight rose around nine times faster. The two did not always move together, which means that watching the scales alone can miss serious metabolic changes in a patient's blood work.

The link between these medicines and metabolic harm was already established. What the paper adds is the timing. Second-generation antipsychotics were known to raise the risk of diabetes and weight gain, but little was pinned down about when the biggest shifts happen. By comparing each patient's own records from before and after the first prescription, the team could show that the opening months carry most of the change.

Who faces the highest risk

Olanzapine stood out among the four medicines. On that drug, blood sugar rose around fifty times faster than before treatment and weight around ten times faster. The differences between drugs matter for prescribing decisions: olanzapine is often chosen when symptoms are severe or other medicines have not worked, and the new figures give doctors and patients a clearer picture of the trade-off in the first months.

People with prediabetes were especially vulnerable. About nineteen percent went on to develop type 2 diabetes within two years of starting the medication, compared with three percent of those whose blood sugar had been in the normal range.

Women bore more of the effect than men. Blood sugar climbed twenty-four times faster in women during that opening window, and weight gain twelve times faster. Both measures rose less steeply in men, though the gap between the sexes was narrower for weight.

What doctors are being asked to do

Lead researcher Juan Carlos Bazo-Alvarez, a senior research fellow at UCL, said the findings point to a practical change in routine care. He described the opening period as "a key period when changes linked to diabetes and weight gain can begin," and said clinicians should check both weight and blood sugar before treatment starts and again during the first few months afterwards.

"By checking blood sugar and weight early, doctors may be able to spot problems sooner and offer support, advice, or treatment to help prevent more serious health issues later on," Bazo-Alvarez said in a statement. He added that the results could help clinicians focus extra attention on the groups shown to be most at risk. The recommendation is deliberately simple: a blood test at the start, then repeat checks in the months that follow, so that a rising HbA1c can be caught before type 2 diabetes takes hold.

Why the timing matters

Second-generation antipsychotics are mainstay treatments for severe mental illness. Schizophrenia affects around 23 million people worldwide, and about 37 million live with bipolar disorder, according to the university's announcement. The researchers stress that the medicines remain valuable; the argument is for closer monitoring, not for avoiding treatment.

The study's size gives the result weight. The pattern held across records spanning more than twenty years of prescribing in England, which makes it harder to dismiss as a quirk of one clinic or one patient group.

The practical message for patients and families is straightforward: ask for a blood test alongside the weigh-in when treatment begins, and make sure both are repeated in the months that follow. Reported by HealthDay and covered widely since the paper's release, the study marks out the window in which early checks can do the most good.

More from the health desk: Severe Asthma Biologics Tied to Fewer Heart Events and Your Daily Walk Might Be Doing More Than You Think.

Sources: University College London; Drugs.com / HealthDay.