David A. Grogan | CNBC. The value of the marijuana market is expected to reach $21 billion in the U.S. by 2020, up from $6.7 billion in 2016

Chuck Rosenberg, chief of the Drug Enforcement Administration, said that smoking marijuana should not be considered medical treatment on Wednesday, calling the notion a "joke."

"What really bothers me is the notion that marijuana is also medicinal—because it's not," Rosenberg said in a briefing to reporters, according to CBS. "We can have an intellectually honest debate about whether we should legalize something that is bad and dangerous, but don't call it medicine—that is a joke."

Currently, 23 states and the District of Columbia have laws legalizing marijuana in some form. Four states — Oregon, Washington, Colorado and Alaska — have opted to legalize the drug for recreational and medical use.

An additional 17 states have approved legislation regarding "CBD-only" marijuana, a chemical compound of the plant that has a wide range of medical benefits.

Rosenberg said that people should not conflate recreational marijuana legalization with medical marijuana.

"There are pieces of marijuana—extracts or constituents or component parts—that have great promise," he said. "But if you talk about smoking the leaf of marijuana, which is what people are talking about when they talk about medicinal marijuana, it has never been shown to be safe or effective as a medicine."

The DEA did not respond to requests for comment from CNBC.

The National Cancer Institute has not conducted its own research on marijuana's effect on cancer symptoms and noted that there has not been substantial evidence to inhale or ingest cannabis to treat cancer-related side effects.

Cannabis is also not approved by the U.S. Food and Drug Administration for use as cancer treatment or any other medical condition, according to NCI.

However, some cannabinoids, the chemical compounds within the cannabis plant, have been approved for medical use. Dronabinol and nabilone, both found in marijuana, have been used for chemotherapy-related nausea and vomiting.

Studies in mice and rats have been promising in recent years. Several research projects have determined that cannabinoids may inhibit tumor growth by causing cell death to cancer cells, but having little effect on normal cells.





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