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When people are diagnosed with cancer, their oncologist may talk to them about using cannabis as an adjunct therapy. However, it’s actually friends and family who are more likely to suggest it, as research shows that’s how most information about using cannabis medicinally is shared.
Many people living with cancer use cannabis or medicines that contain cannabinoids, its primary active compounds, to relieve side effects of cancer chemotherapy and radiation treatments, including nausea, vomiting, loss of appetite, and pain. Some even use it to directly fight cancer tumors.
The role of medicinal cannabis in the treatment of cancer is one of the best understood of all its possible uses. The evidence on this page is based primarily on two comprehensive scientific reports commissioned by the US government—the 1999 report of the Institutes of Medicine (IOM) and the 2017 report of the National Academies of Science Engineering and Medicine (NASEM). The NASEM report reflects the consensus conclusions of 16 renowned experts who systematically reviewed over 24,000 studies published since the IOM report and is considered a definitive resource on the state of the research on cannabis and the cannabinoids it contains. Both reports found that cannabis can have a role in cancer treatment as palliative care for nausea, vomiting, and pain.
Another authoritative resource is the National Cancer Institute (NCI), a division of the US National Institute of Health, which classifies cannabis as a Complementary and Alternative Medicine. Experts from this institution note that, in addition to reducing side effects of cancer treatments, medicinal cannabis can reduce anxiety and improve sleep, which may help patients fight off the disease.
How Cannabis Works in the Human Body
The search for how cannabis affects the body led to the discovery in the 1990s of the endocannabinoid system (ECS). Recent research has revealed the ECS to be a master regulator — modulating everything from metabolism and mood to sleep and immune function. For this reason, NIH researchers concluded that it that it may be a target for treating virtually all human diseases, including cancer.
The ECS plays a role in many aspects of cancer and its treatment, including the experience of nausea, vomiting and pain. The ECS also modulates immune response as cancers develop and the body attempts to fight it.
The ECS is responsible for homeostasis or balancing the body’s systems, so its level of function or “tone” influences how we experience pain, hunger, and nausea. More research is needed to fully identify the mechanisms, but evidence indicates an endocannabinoid tone is responsible for regulating nausea and vomiting. For instance, blocking cannabinoid receptors produces nausea and vomiting in humans and animals. Similarly, people who experience motion sickness have been found to have lower ECS function than those who don’t.
Pain is transmitted through the central, autonomic, and peripheral nervous systems, and cannabinoid receptors have been identified as playing a clear role in modulating pain signaling in each of those systems. Cannabinoid receptors are prominent in the part of the spinal cord that processes sensations such as pain. They are also present in peripheral areas of the body, particularly skin layers, where they modulate pain.
While there is still much to learn about the mechanisms of how cannabinoids fight tumors, scientists have described some of the ways the ECS does it. Activating cannabinoid receptors creates chemicals that induce two types of cell death in cancers of several types, including glioma, melanoma, hepatic, pancreatic, and breast cancers. The ways cannabinoid receptors help resist the spread of cancer cells and can limit the blood flow to tumors involve complex cascades of chemicals that are not yet fully understood, but their ability to do so is well established by laboratory studies with cancer cell lines and animals.
Medical Studies on Cannabis & Chemotherapy
Chemotherapy has significant and severe side effects. Even the thought alone of going to another round of therapy can induce nausea and vomiting in patients. It is one of the most abhorred treatments in medicine that is given. Limiting and addressing those side effects would dramatically improve the quality of life of those undergoing chemotherapy, and may even significantly improve compliance.
Nausea and Vomiting
Cannabis is one of the oldest remedies for treating nausea, and the IOM and NASEM reviews of studies conducted since the 1970s concluded that cannabis is effective for controlling nausea and vomiting. Studies have found people generally prefer cannabis-based medicines to pharmaceutical antiemetics.
That fits with the clinical trials that led the US Food and Drug Administration (FDA) to determine THC is safe and effective for treating nausea and vomiting due to chemotherapy. The FDA has approved two THC medications, dronabinol (MarinolTM/SyndrosTM) and nabilone (CesametTM), which are synthetic versions of THC, available in pill or liquid form.
While these FDA-approved medicines contain the same active ingredient as most medical marijuana products, they are not the same in practice. The FDA-approved medicines are taken by mouth, but oral medications can be impossible to keep down for someone who is vomiting uncontrollably. They also have a delay in onset, taking an hour or more to provide relief, and adjusting dosage can be difficult. Nausea as well dramatically decreases absorption as well, making it harder for medications taken orally to have an impact. By contrast, inhaled cannabis delivers the same therapeutic effects within seconds, allowing for more efficient absorption, faster relief, and improved dosage control.
Many people report that whole-plant medical products work better and with fewer side effects than the single-cannabinoid pharmaceuticals. That may be because of how the hundreds of active compounds in the plant work together therapeutically.
Pain is by far the most common qualifying condition for the more than three million Americans currently registered in-state medicinal marijuana programs. Treating pain with medicinal cannabis has been the focus of more than two dozen randomized double-blind placebo-controlled clinical trials involving thousands of participants. Those gold-standard studies have shown that medicinal cannabis is well tolerated and can offer at least moderate alleviation for most types of pain associated with cancer and its treatment, including difficult-to-treat neuropathic pain. The NASEM and NCI found conclusive or substantial evidence for the use of cannabis or cannabinoid medicines for treatment of chronic pain.
Modern investigation of medicinal cannabis in pain treatment includes laboratory experiments, animal studies, and human trials, all of which indicate it can be a safe and effective treatment.
Many of the studies with people using inhaled cannabis to treat pain were conducted by the Center for Medicinal Cannabis Research, a consortium of university research scientists. Their studies targeted neuropathic pain from various sources, including spinal injury, diabetes, and HIV. They also tested cannabis in experiments where they induced pain, which showed a dose-dependent relationship in which lower doses of THC relieved pain but higher doses produced hyperalgesia, increased sensitivity to pain. In all cases, inhaled cannabis and modest doses were effective in controlling pain.
Cannabis can also work well in combination with other analgesics. Studies show that medicinal cannabis can make opioids more effective at lower doses. A “substitution effect” in which patients reduce opioid use once medicinal cannabis is added has been identified in surveys and a study of people living with pain. A study of opioid prescribing patterns in the US found significant reductions in the number of prescriptions written after states launch medicinal cannabis programs.
As more people living with cancer have turned to cannabis as a treatment, anecdotal reports have accumulated of success with reducing tumors and even achieving remission. These reports are consistent with the several hundred laboratory studies with animal models of cancer and human cancer cell lines. The National Cancer Institute lists information on some of these preclinical studies that demonstrate the anti-tumor properties of cannabinoids.
Scientists have identified several ways that cannabinoids act selectively on cancer cells, including shutting off the blood supply to tumors, preventing the spread of cancer cells, and reprogramming cancer cells to die off. Cannabinoids have been shown to be effective fighting many types of cancer, including those of the brain, skin, blood, breast, colon, liver, and lung.
Only a few human trials have attempted to use medicinal cannabis to directly fight cancer tumors, but results have been promising and align with anecdotal reports and the many preclinical studies. Many people who use cannabis to fight cancer take relatively high doses of THC as oral extracts, as much as 1,000mg/day, about 100-times a standard 10mg dose. Ramping up to a dose in that range can be challenging, as higher doses are more likely to produce psychoactive effects that can be unpleasant. With experience, many people learn how to compensate for those effects. As with other therapeutic effects, studies indicate that THC and CBD in combination have more success fighting tumors.
As effective as cannabinoids appear to be in selectively killing tumor cells, they may also act to protect healthy cells. Scientists speculate that the anti-inflammatory and anti-proliferation effects of cannabinoids may help protect against several types of cancer.
Potential side effects of cannabis use
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