That's also why I can't take medical cannabis serious. With medicine you want exact doses and cut all stuff that's potentially giving by-effects. So what you want is e.g. https://en.wikipedia.org/wiki/Nabiximols
That's not how it works though. Many of the people running the cannabis studies have mentioned that the THC or CBD cannabanoids don't work alone. Cannabis has over 100 such cannabanoids. Nobody is definitively certain of the effects of this list outside of the 5 main ones.
So "cutting all stuff that's potentially giving by-effects" is idealistic and not currently possible without reducing the efficacy of the cannabis.
There are about 113 cannabinoids in weed, while that pot spray only contains 2. With reefer, exact doses do not matter because unlike most medicine, its active ingredients are endogenous and non-toxic.
I'm sorry that 420 culture causes your bias, but that's not a fault of the plant.
So "cutting all stuff that's potentially giving by-effects" is idealistic and not currently possible without reducing the efficacy of the cannabis.