Guanfacine is approved to treat ADHD in the United States and several other countries.
Technically, extended-release Guanfacine is approved because that's what was used in the trials. The brand name is Intuniv and the generic is Guanfacine ER.
The generic guanfacine (non-ER) can also be used, though technically off label. The only difference is that it must be dosed twice a day instead of once a day and the absorption is different so you can't do a 1:1 translation of your dose to the ER.
Now that Guanfacine ER is generic and cheap, you might want to consider it for once daily dosing.
The non-stimulant medications are very good, but require some patience to get started with. Too many people give up in the first week or month because the side effects haven't settled yet. Straterra (Atomoxetine) is another one that can take 1-2 months for good efficacy. Clinical trials show the positive effects continue to build over the course of a year. Surprisingly, Atomoxetine has a lower relapse rate after discontinuation too, suggesting it might be making some long-term positive changes to the brain. This is a nice contrast to stimulants, where the patient becomes essentially dependent on the medication and can go through a protracted rebound if they ever have to discontinue.