Too Much Leucovorin?

My son is 5 | Lvl 2 emerging verbal, and he started on Leucovorin in July 2025. We slowly titrated up every 4-6 weeks with the schedule below.

Sunday, August 10: 5mg to 10mg

Sunday, September 14: 10mg to 20mg

Friday, October 22: 20mg to 30mg

Friday, December 5: 30mg to 40mg

I had noticed that his attention span and just overall ability to concentrate had gotten worse but I wasn’t sure what to attribute it to. During his increase in October, his BCBA went on maternity leave the same day, which resulted in a few of his RBTs getting shuffled around, so we didn’t have continuity of care or any BCBA with a deep repertoire with him, so not a lot of people to report changes in behavior since they hadn’t been close to him. It was also around this time that his neurologist who prescribed him the Leucovorin left the practice we go to.

Fast forward to today, I met with his in-clinic speech therapists (we meet once a quarter but missed January because my son was in the hospital with the flu) and they noted that he was regressing in several areas that he had mastered, primarily due to more stimming and not being able to concentrate. I asked when they noticed and they said early November and it had only gotten worse since then. Immediately, I thought, his leucovorin dose is / was too high.

My question is, has anyone else who has their kids on Leucovorin seen any side effects if the dose is too high? We are going to bring him down on it gradually and keep him at 2 mg to see how he responds over the next few months, but my heart breaks knowing that the dose was likely too high, and we didn’t catch it sooner.