The 2014 Farm Bill legalized the sale of "non-viable hemp material" grown within states participating in the Hemp Pilot Program. This legislation defined hemp as cannabis containing less than 0.3% of THC delta-9, grown within the regulatory framework of the Hemp Pilot Program. The 2018 United States farm bill allowed for interstate commerce of hemp derived products, though these products still fall under the purview of the FDA.
There has been little high-quality research into the use of cannabidiol for epilepsy. The limited available evidence primarily focuses on refractory epilepsy in children. While the results of using medical-grade cannabidiol in combination with conventional medication shows some promise, they did not lead to seizures being eliminated, and were associated with some minor adverse effects.
Selective breeding of cannabis plants has expanded and diversified as commercial and therapeutic markets develop. Some growers in the US succeeded in lowering the proportion of CBD-to-THC to accommodate customers who preferred varietals that were more mind-altering due to the higher THC and lower CBD content. In the US, hemp is classified by the federal government as cannabis containing no more than 0.3% THC by dry weight. This classification was established in the 2018 Farm Bill and was refined to include hemp-sourced extracts, cannabinoids, and derivatives in the definition of hemp.
The e-liquid in vaporizer products usually contains a propylene glycol or vegetable glycerin-based liquid with nicotine, flavoring and other chemicals and metals, but not tobacco. Some people use these devices to vape THC, the chemical responsible for most of marijuana's mind-altering effects, or even synthetic drugs like flakka, instead of nicotine.
The oral bioavailability of CBD is 13 to 19%, while its bioavailability via inhalation is 11 to 45% (mean 31%). The elimination half-life of CBD is 18–32 hours. Cannabidiol is metabolized in the liver as well as in the intestines by CYP2C19 and CYP3A4 enzymes, and UGT1A7, UGT1A9, and UGT2B7 isoforms. CBD may have a wide margin in dosing.
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Some manufacturers ship CBD products nationally, an illegal action which the FDA did not enforce in 2018, with CBD remaining the subject of an FDA investigational new drug evaluation, and is not considered legal as a dietary supplement or food ingredient as of December 2018. Federal illegality has made it difficult historically to conduct research on CBD. CBD is openly sold in head shops and health food stores in some states where such sales have not been explicitly legalized.
There are thousands of unique varieties of hemp. The cultivars used for CBD oil contain significantly higher concentrations of CBD than others. Using these uniquely potent plants, it is possible to extract cannabis oil that contains significant levels of cannabidiol, as well as essential vitamins, minerals, fatty acids, terpenes, flavonoids, and other non-psychoactive cannabinoids.