There's no formula for such dosage. On the bright side, you're only transmitting the information of the substance, not all the nastiness. For instance, you might transmit THC, which might help inflammation. But you'll never get high from it.
The body will take what it can use and pretty much ignore the rest. And it depends on your level of sensitivity. If you're more sensitive, you might need less time or you might start getting a headache.
In any case, it's still safe.
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