Dating back to the mid 1970’s research studies conducted on humans have administered anywhere from 5mg/kg a day to 200mg/kg a day of CBD. Studies demonstrated that sedative effects were observed in healthy volunteers with high CBD dose of 600 mg daily. The effect of CBD is be biphasic, where low doses ( ex/ 15 mg daily) of the cannabinoid appears to have alerting properties instead. There is no scientific data supporting dosage quantities as a daily supplement for CBD however, I would recommend to start by taking 2-15 mg a day.
I am frequently asked "how much CBD should I take?" The answer is that there is no medical literature on which to base a response. Reports of CBD being beneficial in certain conditions have included some information regarding the dosage used, but no evidence is yet available of the kind that supports a particular dose for particular conditions in the way pharmaceutical dosages are determined. We do know that CBD is remarkably non-toxic, and essentially no reports of poisoning from taking too much CBD have appeared in the medical literature either. This makes it very much in the realm of folk medicine to consider using CBD the way one uses supplements "to maintain a healthy lifestyle." While I don’t expect that to cause harm, I can’t base any recommendation one way or another on clinical science.