How long does it take for Nutri adrenal extra tablets to work?

I have been told by a doctor i have to come off my thyroxine tablets for 3-4 weeks at the least while i am in the nutri adrenal tablets otherwise it's dangerous to be on both at the same time. I read that it takes months for them to work so surely taking them for 3-4 weeks won't be long enough? I don't want to have to be off thyroxine for very long because of my symptoms.