Hempseed oil is manufactured from varieties of Cannabis sativa that do not contain significant amounts of tetrahydrocannabinol (THC), the psychoactive element present in the cannabis plant. This manufacturing process typically includes cleaning the seed to 99.99% before pressing the oil. There is no THC within the hempseed, although trace amounts of THC may be found in hempseed oil when plant matter adheres to the seed surface during manufacturing. The modern production of hempseed oil, particularly in Canada, has successfully lowered THC values since 1998. Regular accredited sampling of THC in Canadian hemp seed oil shows THC levels usually below detection limit of 4 ppm (parts per million, or 4 mg/kg). Legal limit for THC content in foodstuffs in Canada is 10 ppm. Some European countries have limits of 5 ppm or none-detected, some EU countries do not have such limits at all.
A 2016 literature review indicated that cannabidiol was under basic research to identify its possible neurological effects, although as of 2016, there was limited high-quality evidence for such effects in people. A 2018 meta-analysis compared the potential therapeutic properties of "purified CBD" with full-plant, CBD-rich cannabis extracts with regard to treating refractory (treatment-resistant) epilepsy, noting several differences. The daily average dose of people using full-plant extracts was more than four times lower than of those using purified CBD, a possible entourage effect of CBD interacting with THC.
Since the 1960’s, medical research has collected research supporting the safety of CBD. Typical doses of 10mg to 100mg a day show no negative effects. Even one study where patients took 1,280 mg a day did not see a problem. The director of the National Institute of Drug Abuse has stated that CBD oil is safe, and recently the FDA approved CBD oil for use in children with epilepsy.