You Don’t, as with any and all Cannabinoids everybody is different. Because there has been an all out ban on the plant now for 70 years plus there is very little scientific research available comparative to the plants properties and it’s connection to the body. Sure, studies have been done but most of the real evidence rests in the past and it will take time for that evidence to be scientifically documented now that research is beginning. The trick with Cannabinoids is how much does it take to affect you, how much does your body need and what combination or profile. The good news is if you live in a legal state you can use cannabinoids with THC if needed and find your sweet spot. I could go on for days with tails of dosages for different people from a mg to a gram (that’s a one thousand times spread) I’ve seen it all and the only thing I can say for sure is everyone is different, what matters is the type and amount of AI (active ingredient) inside. That’s the number you see when you buy cannabinoids, it’s called milligrams or MG. It’s really simple, divide the MG by the volume of the carrier (oil, vape, etc) and you have the concentration. 1mg per ml is .1% concentration, that’s right .1% so, 5mg per ML is .5% where 50mg per ML is 5% So if you bought 30mg per ml which is 3% that means there should be 900 mg in a 30 ml bottle or 1800 mg in a 60ML bottle, 30 ml is about an ounce for reference. 
So back to the question, how do you know it works? You try it, you start small and work your way up, you watch and listen to your body. This isn’t an overnight fix, it takes time, sometimes weeks or even months, everybody is different. With that being said you may notice results right away, there is no way for anyone to know other that you. The best thing I can say is, just start using it, your body will let you know how much you need. There’s one thing for sure, there is no known incident of overdose from Cannabinoids in the plants 10,000 year relationship with man, so that being said it really comes down to why haven’t you tried this (again a whole new topic).
