Medical cannabis has a long history as a natural analgesic,  and is now legal in 30 U.S. states, [2, 3] the majority of which allow limited use of medical marijuana under certain medical circumstances. The medicinal qualities of marijuana are primarily due to high amounts (about 10 to 20 percent) of cannabidiol (CBD), medicinal terpenes and flavonoids.
Tetrahydrocannabinol (THC) is the psychoactive component of marijuana that makes you feel “stoned,” but it too has valuable medical benefits, so depending on your problem, you may want higher or lower levels of THC. Cannabinoids interact with your body by way of naturally occurring cannabinoid receptors embedded in cell membranes throughout your body.
There are cannabinoid receptors in your brain, lungs, liver, kidneys, immune system and more. Both the therapeutic and psychoactive properties of marijuana occur when a cannabinoid activates these cannabinoid receptors.
Cannabis Has Long History of Use for Pain, Seizures and More
The U.S. government, through the Department of Health and Human Services (HHS), actually holds a patent on CBD as an antioxidant and neuroprotectant — an ironic and paradoxical situation considering the U.S. Drug Enforcement Administration has classified cannabis as a Schedule 1 controlled substance, which by definition has no accepted medical use.
This federal classification also makes it very difficult, time consuming and expensive to study the health effects of marijuana. Labs have to jump through a lot of legal hoops before being granted permission to study Schedule 1 drugs. Despite such difficulties, a number of studies have found a wide range of uses for the herb. For example, The Journal of Pain,  a publication by the American Pain Society, has a long list of studies on the pain-relieving effects of cannabis.
Cannabis also has been used for over 80 years for drug-resistant seizure disorders. In January 2015, the American Academy of Pediatrics updated its policy statement on marijuana,  acknowledging that cannabinoids “may currently be an option for … children with life-limiting or severely debilitating conditions and for whom current therapies are inadequate.”
According to the National Institute on Drug Abuse,  which also has information relating to the medicinal aspects of marijuana, preclinical and clinical trials are also underway to test marijuana and various extracts for the treatment of a number of diseases, including autoimmune diseases such as multiple sclerosis and Alzheimer’s disease, inflammation, substance use disorders and mental disorders.
Cannabis Shows Promise as Anticancer Agent
Doctors working with medical cannabis are also using it to treat cancer-related side effects, and evidence suggests the herb may even have antitumor effects all on its own, with dozens of studies pointing to marijuana’s effectiveness against many different types of cancer, including brain cancer, breast, prostate, lung, thyroid, colon and pituitary cancer, melanoma and leukemia.
It fights cancer via at least two mechanisms that make it difficult for a cancer to grow and spread: It’s proapoptotic (meaning it triggers apoptosis or cellular suicide of cancer cells while leaving healthy cells untouched) and antiangiogenic (meaning it cuts off a tumor’s blood supply). As recently reported by Scientific American: 
“… while the available data are limited, research that has been conducted around antitumor effects of cannabinoids so far shows great promise. The International Journal of Oncology published a study  last year, for example, indicating that cannabinoids successfully kill cancer cells, and the benefits increase when combined with chemotherapy.
An early preclinical study  we recently conducted also found that cancer cells derived from patient blood samples were differentially sensitive to the two main active compounds in cannabis — tetrahydrocannabinol (THC) and tetrahydrocannabinolic acid (THCA).
A number of other laboratory and animal studies have been conducted in recent years on colon, breast and brain cancers.  They indicate that cannabinoids may inhibit tumor growth by blocking cell growth, causing cell death and blocking the development of blood vessels that tumors require to grow.”
CBD and THC Combo Improve Anticancer Drug Effectiveness
According to the International Journal of Oncology study mentioned, phytocannabinoids ” possess anticancer activity when used alone, and a number have also been shown to combine favorably with each other in vitro in leukemia cells to generate improved activity.” The best results were obtained when the cannabinoids were paired with the leukemia drugs cytarabine and vincristine.
“Results show a number of cannabinoids could be paired together to generate an effect superior to that achieved if the components were used individually,” the researchers write, noting that CBD and THC together appeared to be more effective than either of them in isolation.
They also found that the sequence of administration mattered a great deal. When cannabinoids were administered after chemotherapy, it induced greater apoptosis or programmed cell death. When administered before, the opposite effect was achieved. According to the authors:
“Our results suggest that when certain cannabinoids are paired together, the resulting product can be combined synergistically with common anti-leukemia drugs allowing the dose of the cytotoxic agents to be dramatically reduced yet still remain efficacious. Nevertheless, the sequence of drug administration is crucial to the success of these triple combinations and should be considered when planning such treatments.”
Hemp CBD Shows Promise Against Ovarian Cancer
Another recent study suggests CBD from hemp may be helpful against ovarian cancer. Hemp and marijuana plants are in the same family but differ in their THC content. While marijuana plants contain varying amounts of THC, hemp contains very little or none of this psychoactive ingredient. According to a report in Medical News Today,  Sullivan University College of Pharmacy in Louisville, Kentucky, is “a hotbed of research into hemp’s potential ability to fight cancer.”
Two of its laboratory researchers recently presented findings from two of its studies at the American Society for Biochemistry and Molecular Biology conference in San Diego. In the first,  a strain called Kentucky hemp was found to reduce the ability of ovarian cancer cells to migrate, suggesting it could eventually be used to help prevent ovarian cancer metastasis.
The second study  found Kentucky hemp reduced secretion of interleukin IL-1 beta in ovarian cancer cells, thereby lowering inflammation associated with cancer progression. What’s more, the researchers found Kentucky hemp “slows ovarian cancer comparable to, or even better than, the current ovarian cancer drug Cisplatin.” The team is now planning additional studies using mice, with the hope of eventually graduating into human trials.
Cannabis Versus Opioids
As mentioned, cannabis has well-proven analgesic properties, and evidence suggests it can be very helpful for those struggling with opioid addiction as well, easing withdrawal symptoms. In one recent study, [15, 16,17] 138 seniors (ages 61 to 70) with osteoarthritis, stenosis or chronic hip or knee pain were prescribed medical marijuana to assess the effectiveness of the herb against pain, and whether it would have any impact on opioid use.
Eighteen percent of the patients moderately decreased their use of other pain killers; 20 percent significantly reduced opioid use and 27 percent stopped using opioids altogether. In all, 91 percent said they would recommend cannabis to others. Forty-five percent of the patients in this study used vaporized oil, 28 percent used pills and 17 percent used marijuana-laced oil topically. Twenty-one percent used cannabis once a day, 23 percent twice a day, and 39 percent used it more than twice daily.
The results were presented at the May 3 annual meeting of the American Geriatrics Society in Orlando, Florida. In an anonymous statement, one of the participants wrote, “My quality of life has increased considerably since starting medical marijuana. I was on opiates for 15 years, and six months on marijuana, [I’m] off both completely.”
Coauthor Dr. Diana Martins-Welch, a physician in the Division of Geriatric and Palliative Medicine, Department of Medicine at Northwell Health, also noted she’s been able to get patients off opioids using medical marijuana.
Cannabis Legalization Has Led to Significant Decrease in Opioid Overdose Deaths
Another major benefit of cannabis is the fact that there’s no risk of overdose or death. In fact, research from the Rand Corporation shows a 20 percent decline in opioid overdose deaths in states that had legalized medical marijuana, suggesting legalizing medical marijuana nationwide could save up to 10,000 lives a year. Together, these benefits make it a lead contender in the fight against rampant opioid abuse and escalating overdose deaths. 
CNN chief medical correspondent Dr. Sanjay Gupta recently published an open letter to U.S. attorney general Jeff Sessions, urging Sessions to change his stance on cannabis to help rein in the opioid epidemic. “Not only can cannabis work for a variety of conditions such as epilepsy, multiple sclerosis and pain, sometimes, it is the only thing that works … It is time for safe and regulated medical marijuana to be made available nationally,” Gupta writes, adding:
“[P]erhaps most important, the compounds found in cannabis can heal the diseased addict’s brain, helping them break the cycle of addiction. There is no other known substance that can accomplish all this. If we had to … design a medicine to help lead us out of the opioid epidemic, it would likely look very much like cannabis.”
Cannabis Eases Depression, Anxiety and Stress
Other recent research  shows cannabis can help ease symptoms of depression, anxiety and stress. Unfortunately, depression and high stress are not recognized as a qualifying condition for a medical cannabis card in most states that have legalized the herb for medical use. The reason for this is largely due to lack of scientific support, Carrie Cuttler, Ph.D., author of the study, says.
To evaluate the effectiveness of cannabis for mental health, the team analyzed data from Strainprint, a mobile application cannabis users can use to track changes in symptoms after using different doses and cannabis chemotypes. Overall, self-reported symptoms of depression decreased by 50 percent and perceived stress decreased by 58 percent with use of medical marijuana.
Of those who inhaled cannabis, over 89 percent reported a reduction in depression; nearly 94 percent reported lower anxiety and over 93 percent reported fewer stress symptoms.
The greatest stress reduction was achieved after 10 puffs or more, while just two puffs reduced symptoms of depression and anxiety. These are rather impressive results, but the authors do note that results “may be inflated in the present sample because those who regularly have symptom exacerbation following cannabis use may be less likely to continue to use it to treat their symptoms and track symptom changes over time.”
Other studies have also shown cannabis can be very helpful for those struggling with post-traumatic distress disorder. [20, 21] Marijuana suppresses dream recall, so for those having nightmares, it can be transformative. Marijuana is also reported to help individuals stay focused in the present, which is beneficial for those experiencing flashbacks.
THC Appears Particularly Beneficial Against Dementia
Interestingly, animal research  has shown THC — the psychoactive component of marijuana — has a particularly beneficial influence on the aging brain. [23, 24] Rather than dulling or impairing cognition in the elderly, THC appears to reverse the aging process and improve mental processes, raising the possibility it might be useful for the treatment of dementia.
To test the hypothesis, mice were given a small daily dose of THC over the course of one month at the age of 2 months, 12 months and again at 18 months of age. It is important to understand that mice typically live to be about 2 years old. The dose was small enough to avoid any psychoactive effects.
Tests assessed the animals’ learning, memory, orientation and recognition skills. Curiously, the 18-month-old mice given THC demonstrated cognitive skills equal to 2-month-old controls, while the placebo group suffered cognitive deterioration associated with normal aging.
According to one of the authors, neurobiology professor Andreas Zimmer, University of Bonn, “The treatment completely reversed the loss of performance in the old animals. We repeated these experiments many times. It’s a very robust and profound effect.” Even more remarkable, gene activity and the molecular profile in the brain tissue was that of much younger animals.
Specifically, neurons in the hippocampus grew more synaptic spines — points of contact necessary for communication between neurons. According to Zimmer, the THC appeared to have “turned back the molecular clock” in the THC-treated animals. (Previous research has also shown that the brain ages much faster in mice who do not have functional receptors for THC, suggesting THC may be involved in the regulation of the aging process. ) The team is planning tests to see if the same holds true in human subjects.
In an earlier study, researchers at the University of South Florida and Thomas Jefferson University found that low-dose THC also directly impedes the buildup of beta amyloid plaque in the brain, [26, 27] which is associated with the development of Alzheimer’s, and enhances mitochondrial function in the brain.
Medical marijuana is also known to reduce some of the non-memory-related symptoms typically experienced by Alzheimer’s sufferers, including anxiety, irritability and rage,  so cannabis may well have multiple benefits for those with dementia and Alzheimer’s.
Is Cannabis Right for You?
While recreational use of marijuana is not advocated, it seems quite clear that certain strains grown specifically to boost medicinal qualities can have a significantly beneficial effect on a number of different ailments and diseases, including chronic pain. In 2010, the Center for Medical Cannabis Research released a report  on 14 clinical studies about the use of marijuana for pain, most of which were FDA-approved, double-blind and placebo-controlled.
This report revealed that marijuana not only controls pain well, but in many cases, it actually does so better than pharmaceutical alternatives. When cannabis is inhaled, smoked or vaporized, its effects are rapid and short-lasting. Orally, it’s the most unpredictable and delayed. When ingesting it, it can take up to two hours to take effect, but if dosed appropriately, you can achieve once-a-day dosing with an edible medicine.
Compared to opioids and many other drugs, cannabis is also far safer. Cannabidiol has no toxicity and it’s virtually impossible to die from marijuana. It’s also self-limiting, as excessive doses of THC will provoke anxiety, paranoia and nausea. Such side effects will disappear as the drug dissipates from your system without resulting in permanent harm, but it’ll make you think twice about taking such a high dose again. Make the same mistake with an opioid, and chances are you’ll end up in the morgue.
Just be sure to seek out a knowledgeable cannabis physician, as the proper dosing needs to be carefully ascertained. If you are seriously considering medical cannabis for pain, please see my interview with Dr. Alan Frankel, one of the leading medical cannabis physicians in the U.S. He can do consultations on the phone if you need specific questions answered.
You can also learn more by reviewing my interviews with Dr. Margaret Gedde, who runs an alternative medical practice in Colorado where they specialize in the use of cannabis, and Todd Harrison, an attorney whose expertise is Food and Drug Law, in which he discusses the current legal status of CBD oil.
Research relating to the use of cannabis can also be found on cancer.gov [30, 31] (the U.S. government’s site on cancer). Simply enter “cannabis” into the search bar. You can also peruse the medical literature through PubMed,  which is a public resource (again, simply enter “cannabis” or related terms into the search bar).