Only one clinical trial has ever been published on the effects of Delta9-THC on cancer growth in humans.122 Doctors administered oral Delta 9-THC to nine patients who experienced tumor progression despite surgical therapy and radiation treatments. The major finding of the study was that Delta 9-THC was safe and did not cause any obvious psychoactive effects in a clinical setting. Furthermore, extensive pre-clinical research clearly indicates that cannabinoids can have tumor-reducing and anti-cancer properties.
One of the most widely studied therapeutic applications for cannabis and the pharmaceutical drugs derived from cannabinoids is in the treatment of nausea and vomiting associated with cancer chemotherapy. Numerous clinical and preclinical studies conducted over nearly three decades have consistently reported that the use of cannabis reduces pain, nausea, vomiting, and stimulates appetite, thereby reducing the severity of cachexia, or wasting syndrome, in patients receiving chemotherapy treatment.
The 1999 Institutes of Medicine report noted that for “patients already experiencing severe nausea or vomiting, pills are generally ineffective, because of the difficulty in swallowing or keeping a pill down, and slow onset of the drug effect. Thus an inhalation (but, preferably not smoking) cannabinoid drug delivery system would be advantageous for treating chemotherapy-induced nausea.” For certain individuals unresponsive to conventional anti-emetic drugs, the use of smoked or vaporized cannabis can provide relief more effectively than oral THC (Marinol) which may be difficult to swallow or be vomited before taking effect. The IOM report concluded, “nausea, appetite loss, pain and anxiety … all can be mitigated by marijuana.”
A 1997 inquiry by the British Medical Association found cannabis more
effective than Marinol, and a 1998 review by the House of Lords Science
& Technology Select Committee concluded that “Cannabinoids are
undoubtedly effective as anti-emetic agents in vomiting induced by
anti-cancer drugs. Some users of both find cannabis itself more
In 2009, a clinical trial involving 177 patients, with intractable cancer pain and experienced inadequate relief from opiates, showed remarkable reductions in pain scores from using a cannabis extract which contained THC and CBD. This THC:CBD extract was more effective than an extract containing only THC.136
The effects of cannabis may also provide an improvement in mood. In addition to THC, other cannabinoids on the plant such as CBD, can inhibit the side effects of THC, as well provide relief from anxiety and depression. By contrast, several conventional medications commonly prescribed for cancer patients, e.g. phenothiazines such as haloperidol (known as “major tranquillizers”) may produce unwanted side effects such as excessive sedation, flattening of mood, and/or distressing physical “extrapyramidal” symptoms such as uncontrolled or compulsive movements.
Scientists have established that the anti-cancer properties of cannabinoids are mediated through cannabinoid receptors. CB1 and CB2 cannabinoid receptors are abundantly expressed throughout the human body, making them an excellent target for disease treatment. Research on the complex interactions of endogenous cannabinoids and receptors is leading to greater scientific understanding of the basic mechanisms by which cancers develop. Research studies on pituitary cancers suggest that cannabinoids may be the key to regulating human pituitary hormone secretion that affects tumor development.
The mechanism of the anti-cancer activity of cannabinoids has been repeatedly demonstrated with breast cancers, with numerous studies showing that cannabinoids are effective in fighting breast cancer tumors and metastization.
Recent research has found that the non-psychoactive cannabinoid cannabidiol (CBD) inhibits the invasion of both human cervical cancer and human lung cancer cells. By manipulating cannabidiol's up-regulation of a tissue inhibitor, researchers may have revealed the mechanism of CBD's tumor-fighting effect. A further in vivo study demonstrated "a significant inhibition" of lung cancer metastasis in mice treated with CBD.
In 2009, scientists reported on the anti-tumor effects of the cannabinoid THC on cholangiocarcinoma cells, an often-fatal type of cancer that attacks the liver's bile ducts. They found that "THC inhibited cell proliferation, migration and invasion, and induced cell apoptosis." At low levels, THC reduced the migration and invasion of cancer cells, while at high concentrations, THC triggered cell-death in tumors. In short, THC reduced the activity and number of cancer cells.
Laboratory research on the effects on cancer tumors of the non-psychoactive cannabinoid cannabidiol (CBD) has found that it inhibits human glioma and glioblastoma multiforme cells, the most common and aggressive forms of brain cancer, in part by cutting of blood supply to tumors. Research on cannabinoids and gliomas, a type of aggressive brain cancer for which there is no cure, holds promise for future treatments. A study that examined both animal and human glioblastoma multiforme (GBM) tumors, the most common and aggressive form of brain cancer, describes how cannabinoids controlled glioma growth by regulating the blood vessels that supply the tumors.182 In another study, researchers demonstrated that the administration of the non-psychoactive cannabinoid cannabidiol (CBD) significantly inhibited the growth of subcutaneously implanted U87 human glioma cells in mice. The authors of the study noted that "... CBD was able to produce a significant antitumor activity both in vitro and in vivo, thus suggesting a possible application of CBD as an antineoplastic agent.183 The targeted effects of cannabinoids on GBM were further demonstrated in 2005 by researchers who showed that the cannabinoid THC both selectively inhibited the proliferation of malignant cells and induced them to die off, while leaving healthy cells unaffected.184 While CBD and THC have each been demonstrated to have tumor-fighting properties, research published in 2010 shows that CBD enhances the inhibitory effects of THC on GBM cell proliferation and survival.
Similarly, researchers reported in 2010 that the way cannabinoid and cannabinoid-like receptors in brain cells "regulate these cells' differentiation, functions and viability" suggests cannabinoids and other drugs that target cannabinoid receptors can "manage neuroinflammation and eradicate malignant astrocytomas," a type of glial cancer.186 This research confirms the findings of multiple studies which have indicated the effectiveness of cannabinoids in fighting gliomas.
Indications of the remarkable potential of cannabinoids to fight cancer in humans have also been seen in three large-scale population studies done recently. The studies were designed to find correlations between smoking cannabis and cancers of the lung, throat, head and neck. Instead, the researchers discovered that the cancer rates of cannabis smokers were at worst no greater than those who smoked nothing at all or even better.195 One study found that 10-20 years of cannabis use significantly reduced the incidence of head, neck and throat cancers.196 Researchers suggest that cannabinoids my produce a prophylactic effect against cancer development, as seen in the anti-proliferation effect that has been demonstrated in vitro and in vivo.
While clinical research on using cannabis medicinally has been severely limited by federal restrictions, the accumulated data speaks strongly in favour of considering it as an option for most cancer patients, and many oncologists do. A random-sample anonymous survey conducted by researchers at Harvard Medical School in 1990, years before any states had approved medical use, found that 44 percent of oncologists had recommended cannabis to at least some of their patients, and more said they would do so if the laws were changed. Of the oncologists expressing an opinion in 1990, a majority (54 percent) thought cannabis should be available by prescription.
According the American Cancer Society's data, 1,665,540 Americans will be diagnosed with cancer in 2014.198 At least 400,000 of them will undergo chemotherapy, meaning as many as 200,000 patients annually may have cannabis recommended to them to help fight the side effects of conventional treatments. The authors of the 1999 Institute of Medicine report Marijuana and Medicine: Assessing the Science Base acknowledged that there are certain cancer patients for whom cannabis would be a valid medical option. Current research on cannabinoids has shown that activation of both cannabinoid receptors has a well-established anti-proliferative effect on cancer cells and may also have anti-angiogenic, anti-adhesive, anti-invasive, and anti-metastatic properties. Since cannabinoids are generally well tolerated, and patients do not develop the toxic side effects associated with conventional treatments, more studies are warranted to develop a cannabis-based cancer treatment.