While Queen Mary's School of Medicine Dr Wai Man Liu and researchers were studying the role of cannabis, commonly known as marijuana, in cancer therapy, they discovered the main active ingredient in cannabis, tetrahydrocannabinol, THC, has the potential to destroy leukemia cells and other cancer cells. Cannabis has been well-established and recognized as an effective treatment in the remedy for nausea caused by chemotherapy and as a medication for pain. The researchers, using highly sophisticated microarray technology were able to detect changes in more than 18,000 genes in cells treated with THC, and were able to discover the existence of crucial processes through which THC can kill cancer cells and potentially promote cancer patient survival.

Due to widespread illegal use of cannabis as a recreational drug, its legal or licensed use in medicine is now a controversial issue in most countries. Currently, there are eleven states with effective medical marijuana laws on the books: Alaska, California, Colorado, Hawaii, Maine, Montana, Nevada, Oregon, Rhode Island, Vermont, and Washington. However, the United States federal government does not recognize any legitimate medical use, and state laws have been challenged.

Dr Liu states, "It is important to stress that these cannabis-like substances used in research are far removed from the cannabis that is smoked. These novel compounds have been specifically designed to be free of the psychoactive features, while maintaining anti-cancer action." Medical marijuana for nausea and pain is known to be administered by smoking marijuana.