What scientists know
Leucovorin is a version of folate, which is the vitamin taken by women to prevent birth defects. It has been FDA approved to ameliorate the effects of chemotherapy in those undergoing cancer treatment but evidence linking it to improved autism-related outcomes is lacking.
Leucovorin is also known as folinic acid. Unlike regular folic acid, folinic acid can cross into the brain even when folate transport is impaired. Some studies suggest that folate transport is blocked in some children with autism, resulting in low brain levels of folate, but these findings have been inconsistent. Data suggesting that leucovorin may ameliorate some symptoms of autism come from four small randomized controlled trials indicating varying levels of effectiveness, all using different doses, different outcomes and different ways of measuring those outcomes. In one case, efficacy was reliant on a specific genetic variant. This science is still in very early stages, and more studies are necessary before a definitive conclusion can be reached. While this drug poses no apparent health risks, there is not sufficient data to show that it improves autism symptoms.