yes, you have herbs in pills, tea, tincture (herb on alcohol.. the dose varies from 15-25 drops in a glass of water 3 times a day to for certain people 5 drops in a glass of water 3 times a day is more than enough). Some herbs are put on oil, in example for massages.
Some herbs are unsuited for tea since they are toxic (like taxus .... which they pump an isolated form of the toxic into people's body as a cancer treatment wtf)
There are quite a lot of different ways to apply them, not every way is suited for every herb, as some work better in water and some better in a different way.
I don't know that much about magnesium supplements sorry, but it seems like you'd want it as an overall detox? I can see that using some herbs could cause some detoxification process on the area they work on, however there are better herbs known for detoxing.
Magnesium is however important for a lot of functions in the body, one that has to do with stress, so I understand a bit why they'd put that together.
I don't think they'd counter each other, because if it would it'd lessen how well the ginkgo works. (Plus I don't think magnesium is a mineral that can disturb a lot of processes these days since it is more common to lack it than to have enough of it).
Is there anything else said on what you are looking for?
Also if you don't mind me asking, why are you looking into this?