A British researcher has found that cannabinoids, a term for chemicals derived from marijuana, can kill leukemia cells, and he expects clinical trials for new medications to begin soon.

The findings, published in the October issue of the journal Anticancer Research, show that certain non-psychoactive cannabinoids "resulted in dramatic reductions in cell viability" and "caused a simultaneous arrest at all phases of the cell cycle," according to an abstract posted online.

The study tested six cannabinoids, together and independently, on leukemia cells.

Study author Wai Liu, an oncologist at the University of London's St. George's medical school, told U.S. News the chemicals displayed "potent anti-cancer activity" and, significantly, "target and switch off" pathways that allow cancers to grow.

"There's quite a lot of cancers that should respond quite nicely to these cannabis agents," Liu said. "If you talk about a drug company that spent billions of pounds trying to develop these new drugs that target these pathways, cannabis does exactly the same thing – or certain elements of cannabis compounds do exactly the same thing – so you have something that is naturally produced which impacts the same pathways that these fantastic drugs that cost billions also work on."

Liu stresses that his research focused on chemicals that would not intoxicate patients.

"By using these drugs in combination with each other we can actually get an enhanced effect, and what that means is that we can – after doing some further studies – take this into the clinic and hopefully get the medication that can be used in patients in the next 12 to 18 months," Liu said.

He cautions the treatments might not work on all varieties of cancer and said it's currently unclear if smoking marijuana would have the same benefits.

"When we talk about smoking marijuana versus marijuana in its purest form, it's very difficult to say. I get asked that a lot," Liu said, "I wouldn't say 'smoke marijuana to fight leukemia' only because we don't know how these different chemicals react with each other inside the patient who smokes it."

The National Cancer Institute has funded some research into the effects of cannabis on cancer, including a preclinical study through 2012 that looked at the effects of cannabinoids on slowing breast cancer, spokesman Michael Miller noted. The NCI has not funded research into the effect of the compounds on leukemia.

The NCI's website notes that "[s]tudies in mice and rats have shown that cannabinoids may inhibit tumor growth by causing cell death, blocking cell growth, and blocking the development of blood vessels needed by tumors to grow. Laboratory and animal studies have shown that cannabinoids may be able to kill cancer cells while protecting normal cells."

Preclinical studies show that cannabinoids can cause breast cancer cell death, potentially reduce the risk of colon cancer, damage or kill liver cancer cells and make chemotherapy more effective against glioma cell cancer, which affects the brain or nervous system, according to the NCI website.

The cannabinoids dronabinol and nabilone are approved by the Food and Drug Administration for combating the side-effects of chemotherapy, but no cannabinoids are currently approved for treating cancer itself.

Kris Hermes, a spokesman for the pro-medical marijuana group Americans for Safe Access, said that American scientists looking into cannabinoids "have often given up in disgust" because of "the harsh climate for research" in the U.S.

Hermes says researchers must receive approval from the National Institute on Drug Abuse and also from the U.S. Public Health Service before looking into the plant's possible benefits. NIDA holds a monopoly on cannabis used for research and requires all scientists to use plants grown at the University of Mississippi.

"Very little research is going on in this country mainly because of the obstruction of research by the federal government," Hermes said. "If we want to get ahead of the curve or learn more about this therapeutic substance and bring it to as many people in the U.S. who can benefit from it, we need to break down the barriers to research."

In 2011, ASA produced a report detailing what it calls arbitrary obstruction of research by government officials.

ASA and other drug reform advocates are urging the U.S. government to reclassify marijuana – currently a schedule one substance under the Controlled Substances Act of 1970 – but efforts so far have been unsuccessful. On Oct. 7 the U.S. Supreme Court declined to entertain an appeal from ASA that sought to force reclassification.

According to Liu, who says he does not smoke marijuana, European countries are the primary drivers of cannabis research. He believes business interests may have historically played a role in deterring research into marijuana-derived substances.

"The actual countries that are keen to drive cannabis as an anti-cancer treatment are places like Spain and Italy, as well as the U.K.," he said. "The reason why we believe it to be the case is because the way that these drugs work is very similar to how conventional drugs work."