In a recent survey by the American Society of Anesthesiologists (ASA) of 1,005 adults in the U.S., patients were asked about their personal use of medical marijuana for the treatment of pain. Seventy-five percent of respondents stated they were interested in or have used marijuana or marijuana products for pain management and more than half (62%) believe marijuana and cannabinoids are safer than other pain medications, including opioids.
Marijuana is made from the dried flowers of the cannabis plant. Made of more than 500 chemicals, including over 100 compounds called cannabinoids, the primary active compounds in the plant are tetrahydrocannabinol (THC) and cannabidiol (CBD). THC acts on specific brain cell receptors that react to natural chemicals that play a role in normal brain development and function. These natural chemicals impact the formation of brain circuits that are important for decision making, mood and responding to stress. THC is primarily responsible for the “high” associated with marijuana use and for other mental health effects such as altered senses (seeing bright colors); altered mood, including hallucinations; and even psychoses at higher doses.
A bipartisan bill titled the Medical Marijuana Research Act of 2019 was recently introduced to amend the Controlled Substance Act, allowing faster approvals for medical marijuana research. This bill along with another, the Cannabidiol Research Expansion Act, seek to expand research on marijuana and its compounds.
Given the risks of interactions with other medications and the long-term effects of marijuana use, it is very important for patients to discuss use with their physician. Patients should ask their physician anesthesiologist for a personalized pain treatment plan that incorporates the latest evidence.
When people begin using marijuana as teenagers, the drug may impair thinking, memory, and learning functions. People who begin using marijuana before age 18 are four to seven times more likely than adults to develop a marijuana use disorder. Repeated exposure to THC at a young age can result in the use of other addictive substances (i.e., nicotine, morphine) and an increase in addiction-like behavior. This has led to a warning from the U.S. Surgeon General’s office on marijuana use and the developing brain, advising caution in adolescents and youth, as well as pregnant and breastfeeding women.
An increasing number of studies are demonstrating that cannabis is an effective pain treatment with fewer side effects than many alternatives. However, some reports still claim only “weak” evidence for cannabis’ pain-relieving benefits. Some of these negative effects may stem from the use of high-THC/low-CBD cannabis strains, which are known to induce more adverse side effects and weaken in efficacy with tolerance development.
Neuropathic pain is different from nociceptive pain in that arises from damage to the body’s nervous system. And it’s quite common. Neuropathic pain affects 7-10% of the population and can result from forceful injury, pinching, or stabbing that damages nerves. Disease is also a common underlying cause of neuropathic pain. For example, in multiple sclerosis, the insulation of nerve cells breaks down which leads to neuropathic pain. Other diseases that cause neuropathic pain include Parkinson’s disease, HIV, diabetes, and shingles, to name a few. Chemotherapy is an additional common cause of neuropathic pain due to its destructive effects on many types of cells in the body.
CBD also has a host of targets beyond the endogenous cannabinoid system (ECS) that can relieve pain. Of particular relevance, CBD enhances the activity of receptors for the brain’s primary inhibitory neurotransmitter, GABA. Through this inhibitory effect, CBD can dampen pain signals as they make their way into the brain.
Cannabis and Central Pain
Nociceptive pain (i.e., inflammatory pain) results from tissue damage. It is subjectively described as sharp, aching, or throbbing pain that follows physical damage. When you get injured, the damaged tissues recruit numerous inflammatory and immune cells to repair the damage. These cells release proteins and chemicals that activate receptors on nerves that make their way into the spinal cord and up to the brain, causing the sensation of pain.
Pain results from the coordinated activation of brain cells. While these brain regions lead to the sensation of pain, they can also modulate the strength of the pain signals. In some instances, you can have physical injury (i.e., nociceptive pain) without the sensation of pain (imagine a car accident victim who can walk around pain-free in the initial moments after the accident).
CBD can also improve mood by activating serotonin receptors, which has anxiety- and stress-reducing effects. Since depression and anxiety are common among those in chronic pain, the mood-improving effects of CBD makes it a valuable addition in pain therapy.
The different types of pain fall into three general categories:
A systematic review of the same question – the benefits and adverse effects of medicinal marijuana – was published in the Journal of the American Medical Association (JAMA) last year with similar conclusions – but found the evidence overall to be weaker, and not there at all for anxiety.
Last week’s report from the all-party parliamentary group for drug policy reform recommended medicinal cannabis for chronic pain, spasticity, nausea and vomiting after chemotherapy and for anxiety. There is good evidence to use cannabis products or “natural” cannabis, they said, for all these conditions – and moderate evidence for use in sleep disorders, fibromyalgia and post-traumatic stress disorder. The evidence came from a review based on 20,000 references – although, in places, they were quite generous in their rating of the evidence.
Q ueen Victoria was prescribed cannabis for period pains, and 19th-century American doctors used it for everything from anorexia to sexual problems. And now the US is embracing medicinal cannabis again – it’s legally available in 25 states for conditions such as Aids, anorexia, arthritis, cachexia, cancer, chronic pain, glaucoma, migraine, muscle spasms from multiple sclerosis, seizures and severe nausea. The list is for comparison: in the UK, the only indication for medical cannabis is for painful, tightening muscle spasms (spasticity) in multiple sclerosis. Sativex, an oral spray that uses two chemical extracts from the cannabis plant – delta-9 tetrahydrocannabinol (THC) and cannabidiol (CBD) – was the first medicinal cannabis licensed in the UK. Medicinal cannabis, you see, does not mean treating yourself by smoking weed. Cannabis comes as a proper drug – Sativex costs too much for the health watchdog Nice to recommend and only a handful of specialist doctors will prescribe it.
The evidence shows that cannabis does relieve chronic pain, but the Home Office has already said in response to this latest report that cannabis “is a harmful drug which can damage people’s mental and physical health”. Yet Nice says it works in the treatment of MS. And the JAMA review, which had higher standards of evidence than the latest report, says that cannabis benefits people with chronic pain or spasticity due to MS. It adds that there is some evidence it helps to improve weight gain in HIV infection, and relieves insomnia, nausea and vomiting due to chemotherapy. There is no data on long-term side-effects – psychosis is the most feared. Typical side-effects include drowsiness, nausea, paranoia, sweating and euphoria. There is no solid research comparing “natural” with “medicinal” cannabis, but the research suggests similar benefits for pain and spasticity. So it does work – but the law says you can’t take it.