Nearly a quarter-million American children have experienced gun violence at their schools since the 1999 Columbine massacre. But beyond the grim statistics, the question of how such violence affects survivors over time has long loomed over public discussions about gun violence on campus.

This week, researchers at Stanford’s Institute for Economic Policy Research offered some answers. According to a working paper being billed as the “largest scale study to date" on the issue, antidepressant use among child survivors soared more than 21 percent in the two years after a fatal incident, and grew to 24.5 percent three years out.

The researchers say the findings are a clear indicator of the toll that school shootings have on young survivors, even as they warn that the number of prescriptions is unlikely to capture the full mental health consequences of these events.

“When we think about the cost of school shootings, they’re often quantified in terms of the cost to the individuals who die or are injured, and their families. Those costs are unfathomable and undeniable,” lead author Maya Rossin-Slater said in a statement. “But the reality is that there are many more students exposed to school shootings and survive. And the broad implication is to think about the cost not just to the direct victims but to those who are indirectly affected.”

The team drew its findings from data gathered on the locations of fatal and nonfatal school shootings compiled by The Washington Post. They then examined rates of youth antidepressant prescriptions at pharmacies located within five miles of the affected schools, as tallied in a private commercial database of prescriptions.

When they plotted the data, the trend in antidepressant prescriptions before and after fatal shootings was immediately apparent.

“Antidepressant use in the shooting-exposed areas increases dramatically following a school shooting,” the authors write, particularly when fatalities were involved. The authors noted that the rise in prescription use after nonfatal shootings was statistically insignificant.

To ensure the trend after fatal shootings was not simply coincidence, the team controlled for a number of confounding factors and ran several analyses to confirm the findings. First, they found that there was no effect on youth antidepressant prescriptions at pharmacies located farther than five miles from a school shooting. They also uncovered no evidence of an effect on antidepressant prescriptions for adults: the trend is limited only to the age group most directly affected by a shooting at school.

Furthermore, they found no change in prescribing rates of other types of medication for youth in the affected areas, suggesting that the increase isn’t simply a result of increased interactions with the health-care system overall.

They also note that the effects are smaller in areas with a larger proportion of psychologists and social workers — mental health professionals who typically focus on behavioral interventions rather than prescription-based treatment. The data in the report doesn’t speak to whether one approach is more beneficial than the other for survivors of school shootings.

“Taken together, our results demonstrate that local exposure to fatal school shootings leads to significant and persistent increases in antidepressant use among American youth,” the authors conclude.

The findings are particularly concerning in light of the fact that mental health issues during childhood put an individual at higher risk for a variety of problems as an adult. A 17-year study involving more than 1,000 children and adolescents in North Carolina, for instance, found that children with mental health issues were six times more likely to exhibit problems with “health, the legal system, personal finances, [or] social functioning” as adults.

Some antidepressants also carry unique risks and side effects when they’re prescribed to children and teens, including anxiety, panic attacks and an increased risk of suicidal thinking.

“There are articles that suggest school shootings are the new norm — they’re happening so frequently that we’re getting desensitized to them — and that maybe for the people who survive, they just go back to normal life because this is just life in America,” Rossin-Slater said. “But what our study shows is that does not appear to be the case.”