The weird thing is that drugs are used off label all the time but Kuvan is near next to impossible to get. I got a prescription and the rep told my doctor that she couldn't prescribe it for BH4 deficiency. That's a labeled use in the EU just not here due to the orphan status. It made my doctor so leery that she took the script back. And it used to be available at every compounding pharmacy. It's not like it is particularly dangerous or anything.