The US Food and Drug Administration has approved leucovorin to treat brain folate deficiency but not for autism

The Food and Drug Administration on Tuesday approved a decades-old prescription vitamin called leucovorin as the first treatment for a rare genetic disorder in some adults and children.

The move comes months after the Trump administration touted leucovorin as a potential treatment for a broader group of patients with symptoms of autism spectrum disorder. The claim raised skepticism among some in the medical and research community, but sparked excitement among families, leading to increased prescriptions for the drug in the United States.

An FDA official told reporters Monday that “we don’t have enough data to say we can prove efficacy for autism on a broader scale,” but said the agency is open to companies’ interest in studying leucovorin in autistic populations.

The drug, also referred to as folinic acid, is a synthetic form of vitamin B9 that has been used to treat the toxic side effects of chemotherapy. A few small trials have suggested that leucovorin can be effective as an off-label treatment for children with autism, and some families have reported that it has helped their nonverbal children develop more language and social skills.

FDA officials, who requested anonymity to discuss the decision, told reporters Monday that they had begun a broad review of leucovorin as a treatment for autism before narrowing its approval to a smaller population with cerebral folate deficiency, a rare genetic mutation that prevents folic acid — a key vitamin — from properly reaching the brain.

This condition shares overlapping features with autism, typically develops in young children under the age of 2 and can cause severe developmental delays, seizures, lack of muscle control and other serious neurological complications.

The FDA found that the use of leucovorin in patients with the condition produced “high-quality data” to support the expanded approval, which will apply to both generic versions of the drug and GSK’s old branded drug, Wellcovorin, officials said.

“This was the data where we saw the largest effect sizes,” an FDA official said on the call. “So we narrowed down that group, just because we felt that was the strongest scientific justification and also the largest treatment effects that could be used to overcome some of the limitations in the data sources.”

Approval was based on a systematic review of published literature in the area, including patient case reports, but not a randomized controlled clinical trial. The same official acknowledged the possibility of biases in systematic reviews, but emphasized that the treatment effects were so large that they outweighed those concerns.

Officials added that the FDA is encouraging current manufacturers of leucovorin to increase production to match the growing demand for the drug. While GlaxoSmithKline originally marketed the drug from 1983 until 1997, the company said in September that it had no plans to relaunch the product and manufacture it itself.

In a statement Tuesday, Dr. Tracy Beth Hoge, acting director of the FDA’s Center for Drug Evaluation and Research, said the approval demonstrates the FDA’s commitment to “rapidly identifying effective treatments for extremely rare diseases while maintaining the same standards of evidence for approval.”