Newly released data from the U.S. government suggests that a much larger number of women are using attention-deficit/hyperactivity disorder (ADHD) medication, with the biggest increase observed in young women in their mid- to late 20s.

All in all, the U.S. Centers for Disease Control and Prevention’s latest Morbidity and Mortality Weekly Report published Friday showed that 344 percent more women aged 15 to 44 with private health insurance filled out prescriptions for Adderall, Ritalin, and other ADHD drugs between the years 2003 and 2015. According to ABC News, the biggest increase was observed in women aged 25- to 29-years-old, who filled 700 percent more prescriptions, followed by those between the ages of 30 and 34, where a 560 percent increase was reported.

The CDC report also included information on the types of ADHD medication women had filled out prescriptions for in 2015. Mixed amphetamine salts, which are popularly marketed as Adderall, was the most popular form of medication, followed by lisdexamfetamine (Vyvanse), and methylphenidate (Ritalin). The Guardian added that use of amphetamine-based ADHD drugs made a “dramatic” increase, despite the availability of non-stimulant alternatives, whose usage remained steady in the period covered by the report.

In a statement, CDC National Center on Birth Defects and Developmental Disabilities director Dr. Coleen Boyle said that the figures are concerning because the potentially adverse effects of ADHD medication on pregnancy are still largely unknown.

“Half of all pregnancies in the United States are unplanned, and women may be taking prescription medicine early in pregnancy before they know they are pregnant,” said Boyle.

“Early pregnancy is a critical time for the developing baby. We need to better understand the safest ways to treat ADHD before and during pregnancy.”

Young Women Are Using ADHD Drugs in Greater Numbers, CDC Reports https://t.co/Wvb8Asc9PA — Justin Garczynski (@denkomufuritsu) January 20, 2018

The statistics published by the CDC were gathered from private insurance claims filed by up to 6.8 million women in the United States between 2003 and 2015. As The Guardian further observed, awareness of ADHD has resulted in the number of people diagnosed with the condition increasing through the years, with the huge increases reported by the CDC resulting in the overall percentage of women taking ADHD medication jumping from 1 percent in 2003 to 4 percent in 2015.

In the new report, the CDC did not specify what might have caused the significant uptick in ADHD drug prescriptions among U.S. women. But experts believe that the increase is more of a case of “rightsizing,” as today’s doctors are now more likely to diagnose girls and women with ADHD than they were in the past.

“We’re kind of catching up now,” observed Washington, DC developmental pediatrician Dr. Patricia Quinn, speaking to USA Today.

Melissa Orlov, a marriage counselor whose now-adult daughter was diagnosed with ADHD when she was in the fifth grade, told USA Today that the increase in childhood ADHD diagnoses, regardless of the child’s gender, could explain the increase in diagnoses among adult women, as many women only realize they might have the condition following their child’s diagnosis.

Despite these seemingly valid explanations for the spike in ADHD prescriptions filled by women pointed out on the CDC’s report, medical professionals are still concerned about the lack of studies on the safety of stimulant drugs when used during pregnancy, and these papers’ often contradictory nature. Given these concerns, the CDC’s Boyle advised women to consult their doctor before stopping or starting any form of ADHD medication while pregnant.