My son is on Humira weekly as well as mtx weekly (injection) his dose is equal to 25mg orally.
He has also taken mtx orally in a dose ranging from 7.5mg to 25mg.
Some say there are more of the icky side effects like nausea and flu like feeling from the oral dose since it goes through digestion than with the injection but my son has had no side effects with either.
He does take folic acid daily 1mg, since it is recommended as mtx is a folate antagonist. This is a px not otc.
Also some take zofran too help with side effects.