The subject of marijuana in medical discourse has long been a point of controversy. Over the last several years, marijuana in both recreational and medicinal forms has become increasingly accepted in the US. This article addresses medical marijuana and its potential therapeutic benefits for various neurological conditions. A previous companion article covers Recreational Marijuana and Cognitive Decline: What Every Clinical Neurologist Needs to Know. 

Composition

As of March 2015, a total of 23 states plus the District of Columbia have enacted medical marijuana laws to facilitate access to use marijuana as a treatment for a variety of medical conditions. Currently, two cannabinoids are FDA-approved: Dronabinol and Nabilone. On the docket is the oromucosal spray nabiximols, which is currently under investigation. The former two are available in pill form and are indicated for nausea and vomiting associated with cancer chemotherapy, as well as for appetite stimulation in wasting illnesses such as HIV infection or cancer. Dronabinol is an Isomer of THC and chemically identical to plant-derived THC. It is a schedule lll substance and available in 2.5-10mg oral capsules.

Nabilone is a schedule ll THC analog similar to THC. It is more potent than Dronabinol. It is administered orally in a 0.25, 0.5 or 1mg capsules. Nabiximols has a 1.1 ratio of THC to CBD as an oral-mucosal spray and not FDA approved but approved in 20 other countries including Canada for chronic cancer pain. (Note: Legal medicinal cannabis purchased from dispensaries in the US lacks government-regulated standardization of cultivation, potency, and purity.) In addition, medical marijuana can also be dried material from the cannabis plant consisting of THC, cannabidiol and other cannabinoids. It is purchased from dispensaries in a variety of preparations or grown by patients for different illnesses. Regular pharmacies do not stock it because it is Federally illegal.

Common cannabis preparations for purchase from state approved dispensaries are: Marijuana (dried plant product smoked or vaporized), hashish (concentrated resin cake that is ingested or smoked), tincture (cannabinoid liquid extracted from plant used sublingually), hashish oil (oil from cannabis plant usually smoked or inhaled) and infusion (plant material mixed with nonvolatile solvents such as butter or cooking oil and ingested).

Cannabidiol does not affect memory and helps to curtail THC side effects by CB1 inverse agonist activity.

In terms of vehicle, there is overwhelming preference of medical marijuana use for inhalation over oral ingestion.¹ This is based on rapid absorption, distribution and less prolonged if any side effects. Maximum effect of inhaled cannabis is 30 minutes and some effect is after two minutes. Total benefit is two to three hours. In oral medical marijuana such as dronabinol (available by prescription), peak plasma levels occurs in two hours with a range from 30 minutes to four hours and as a result less popular. Body fat is the main long-term storage site of THC and takes five days to eliminate 80 percent to 90 percent and 13 days to completely eliminate the THC. THC tolerance varies across different brain regions. Tolerance develops after a few doses and then disappears quickly after cessation. Combining low dose of cannabinoid with one or more additional therapeutic medications has also been successful in medical marijuana use.²

Neurological Benefits

The potential benefit of cannabinoid use has been the source of much conjecture within the neurology literature. Fife, et al. stated that, “Overall there is lack of evidence regarding the safety and efficacy of cannabinoid use in many neurological illnesses. Most published studies are surveys, case reports, small case series or non-placebo controlled studies. Many of these studies relied on subjective experience and do not include objective measures. Also, the effects of cannabis are difficult to mask in placebo controlled studies and there is a strong placebo effect. This problem can be reduced by using cannabis preparations lower in THC or those that have fewer psychoactive side effects (eg. CBD).”³ However, it is worth looking at some of the evidence more closely to assess the potential of medical marijuana as a viable treatment option for certain neurological conditions.

Chronic Pain. The neurological condition with arguably the most evidence for the benefit of marijuana is chronic pain. In a recent meta-analysis, researchers investigators assessed 28 random control trials (2,454 participants), 12 that included Neuropathic pain (central/peripheral), three studies for cancer pain, three for diabetic peripheral neuropathy, two studies for fibromyalgia, two studies for HIV sensory neuropathy, and one study for each of the following: refractory pain due to MS, rheumatoid arthritis and other musculoskeletal disorders.4 Overall, the studies showed 30 percent or greater improvement of all above causes of pain using the GRADE approach, especially with cannabinoids (smoked THC and Nabiximols) compared to placebo. The GRADE approach refers to overall quality of evidence for risk of bias, publication bias, imprecision, inconsistency, indirectness, and magnitude of effect.⁴

In another study, investigators reviewed six trials (325 patients) for chronic pain and six trials (396 patients) for neuropathic pain and found similar results. The authors concluded that the use of marijuana for chronic pain, neuropathic pain, and spasticity due to MS is supported by high-quality evidence.⁵ Side effects were very mild and included sedation, fatigue and trouble concentrating. (It is worth noting that many cannabis analgesia studies use a benchmark of more than 30 percent reduction in pain intensity because it has been validated as the threshold necessary for meaningful improvement in quality of life.)

The efficacy of cannabinoids in chronic neurogenic pain management is explained by ECS modulation of the descending supraspinal inhibitory pathway compromised in chronic pain patients. Cannabinoid activation of CB1 and CB2 receptors stimulates the endogenous noradrenergic pathways, which activates peripheral adrenoreceptors to induce antinociception. CB2 receptor stimulation occurs in the dorsal root ganglion sensory neurons, the spinal cord and brain regions highly relevant to nociceptive modulation. In a study published in 2008, researchers investigated the potential of cannabis cigarette in three six hour sessions in 38 patients with complex regional pain type 1, physical trauma to nerve bundles, spinal cord injury, and multiple sclerosis who had smoked previously in which previous cannabis exposure was required.⁸ Low and high THC cannabis produced effective analgesia with comparability suggesting a dose ceiling. The authors stated the effects produced by cannabis were similar to opioid analgesia with improvement of the affective and sensory component but not resulting from a relaxing or tranquilizing effect. In addition, a similar study showed improved sleep quality with higher THC levels in addition to pain relief.⁹ Side effects were more common and very mild in the higher THC dose. These included dizziness, numbness, and cough.

Interestingly, a number of studies looking at chronic neuropathic and non-neuropathic pain have shown prevention or reduction of opioid tolerance of 30 to 50 percent in 43 percent of patients.⁸ Combining opioids and cannabis in pain therapy offers the added potential advantage of synergistic analgesic action that decreases the dosage requirements and side effects of both agents.⁹

Spasticity due to Multiple Sclerosis or Paraplegia due to spinal cord injury. It is well recognized by treating neurologists that spasticity is a core symptom of many of our MS patients. Oral antispasmodics are of limited effectiveness and research in this field for further therapy has not significantly expanded since the 1990s. Consequently, many patients have sought relief in MS through cannabis use. One study showed benefit of spasticity in MS using nabiximols, nabilone, and dronabinol compared to placebo.⁴ One study evaluating 12 trials totaling 1,600 MS patients showed similar results.³ In addition, the AAN published evidence based guidelines that recommended an oral cannabis extract or nabiximols spray both containing THC and cannabidiol (not available in the US as an FDA approved medication) as having the highest level of empirical support as a treatment for spasticity and pain associated with MS.¹⁰ These are the only guidelines that address the use of medical marijuana as a treatment for Multiple Sclerosis.

Movement Disorders. Two small placebo controlled studies (36 participants), suggested that THC capsules may be associated with significant improvement in Tic severity in Tourette’s disease. After very thorough review, the AAN guidelines state that the efficacy of medical marijuana in Tourette’s and cervical dystonia are both unknown. The current opinion in regard to dopamine related dyskinesia in Parkinson’s disease is that it is ineffective.³

Seizure Disorders. The data on medical marijuana in seizure disorders is insufficient due to lack of well-designed studies.³ Despite this, many states that have legalized marijuana have listed seizures as an indication. One agent showing promise is Epidiolex, a plant derived CBD which reduced seizure frequency in doses up to 25mg/kg in drug-resistant patient in a recent open label study.¹¹

Adverse Events

Adverse events and safety of medical marijuana, unlike recreational use, is only available in short-term (less than three months) use. Also comparing chronic recreational from medicinal users is complicated and cautioned because of difference in age of regular users, duration, quantity, THC content, concurrent alcohol and drug abuse and drug delivery approaches.¹² It is also important to remember that medical marijuana is not first-line treatment for neurological disorders like chronic pain and neuropathy or in MS. Current treatments including Opioids, antispasmodic drugs like Baclofen, Tizanadine, and Benzodiazepines can cause many side effects including sedation, impaired balance, and memory impairment.

In a meta-analysis review,⁴ short-term AEs were reported in 62 studies. There were no studies reporting the long-term adverse effects. There was overall no evidence for a difference in the association of cannabinoids or cannabis with the incidence of any AEs based on type of cannabinoids, study design, indication, or duration of follow-up. Common AEs included: balance problems, confusion, dizziness, diarrhea, drowsiness, dry mouth, fatigue, hallucinations, and nausea and vomiting.

Data from a 2008 study data evaluating 1,932 patients with median cannabinoid exposure found serious AEs in 164 cannabinoid patients and 60 controls.¹² The cannabinoids included dronabinol pills and nabiximol spray. The most frequent were respiratory (16.5 percent), gastrointestinal (16.5 percent), and nervous system (30 percent). The difference between cannabinoids and placebo was not statistically different. No serious adverse events were more common in medical marijuana users, with the most common being blurred vision, dry mouth, dizziness, sedation, confusion, and altered mood. Studies that reported smoked medical marijuana found that side effects were dose-related, mild to moderate in severity, time limited, and less common in experienced cannabis users. Most frequent were: dizziness (30 to 60 percent), dry mouth (10 to 25 percent), fatigue (five to 30 percent), muscle weakness (10 to 25 percent), and myalgia (25 percent). Euphoria was not common because the concentration of THC was less than 25 percent of the levels found in recreational use. Tachycardia and palpitations, when they occurred, were transient due to rapid body removal of the THC out of the circulatory system. Higher levels of THC in the medical marijuana caused more sedation and ataxia. Tolerance to side effects of cognition and cardiovascular effects developed rapidly over the initial two to 12 days of therapy.¹² It is worth noting that patients very ill, elderly, and taking multiple medications are more prone to side effects and most of these side effects can be decreased by dose titration.

Suggested treatments for neurological and psychiatric related side effects, include Zyprexa or Haldo for acute psychosis, acute anxious psychotic symptoms, and high THC content use cannabidiol. For cognitive impairment with repeated use, COX-2 inhibitors appear to offer some benefit based on preclinical primate studies.¹⁴ Also among concerns in cultivation are contaminants of the cannabis plant including fungal and bacterial organisms, (concern in immunocompromised patients), heavy metals like aluminum and cadmium from the soil, and organophosphate pesticides. Canada and some European countries are taking charge of all aspects of cannabis cultivation and testing all the products to be sure they are safe before distribution to medical/research workers, however no such process exists in the US.

Pulmonary Risk. What do we know about pulmonary risk of cannabis smoking and is there a difference from tobacco smoking? This is an important question as relates to many of our neurological patients who suffer chronic pulmonary disease at the time of evaluation. Molecules in tobacco smoke enhance carcinogenic pathways through circumventing normal cellular checkpoint protective mechanisms, activation of respiratory epithelial cell nicotine receptors, prevention of apoptotic cell death in cells accumulating genetic damage, and promotion of tumor angiogenesis. Molecules in cannabis smoke do the opposite: they inhibit carcinogenic pathways through down regulation of free radical production; THC blockade of enzymatic conversion of smoke constituents into carcinogens; absence of cannabinoid receptors in respiratory epithelial cells (keeps DNA damage checkpoint unimpaired); and its antiangiogenic, tumor retardant function. A 20-year longitudinal study of pulmonary health in 5,115 cannabis smokers showed that cannabis, unlike tobacco, had no effect on pulmonary function. The same for medical marijuana.¹⁵ Another study looking at 878 Canadians 40 year and older with history of tobacco smoking, or marijuana and tobacco smoking, but not marijuana only smoking, found much higher risk of respiratory and COPD in the tobacco group.16 Additionally, vaporizing systems used for cannabis have been shown to reduce carbon monoxide, polycyclic hydrocarbons, and tar compared to smoking cannabis.

Neurological Impairment. Unfortunately, unlike long-term recreational effects of cannabis on cognition age 40 or less, (as discussed earlier in this paper), no long-term published data exists for medical marijuana users. Likewise, there is no long-term data showing the long-term effects of recreational or medical marijuana on cognition in patients over 50 years of age. A 2013 review on the short and long-term effects on cognitive function in recreational users found that cognitive impairment is unlikely to persist beyond the acute intoxication state even with high TCH cannabis, in late onset users, short-term users, and occasional users.¹⁷

Psychosis And Schizophrenia. The only note pertaining to neurologists in the setting of psychosis and schizophrenia is that cannabis should be avoided in adolescents and adults with current, past, or family history of any psychotic disorders. A subgroup of patients that’s genetically vulnerable to cannabis induced psychosis carry a functional polymorphism in the catechol-o-methyltransferase gene and brain derived neurotrophic factor gene. Otherwise, cause and effect of cannabis use and long term development of psychotic psychiatric disorders has not been established.^1,18

Addiction and Withdrawal. While addiction risk in recreational marijuana users is known (as reported in the Part I of this series in the October 2015 edition of Practical Neurology^®), the risk in medical marijuana is unknown. A safety analysis of all medical marijuana use (nabiximol sprays in RCT studies) showed that no withdrawal symptoms were present in abrupt removal. This may be due to low levels of THC in medical marijuana. In experienced recreational higher dose cannabis users, abuse potential with some mild withdrawal symptoms occurred with medical marijuana.¹⁹

Overdose, Toxicity And Death. In animals and humans it is virtually impossible to induce fatal toxicity and no human fatalities have been reported to date.²⁰ The rare acute complications in an ER setting, such as panic attacks, psychosis, and convulsions, can be managed in a hospital setting (IV benzodiazepines).^21,22 However, children who may ingest cannabis edibles like beverages and candies by mistake represent an exception, since children can develop respiratory depression and coma.

Conclusion

Though it may be hard to believe that marijuana is not only available legally for recreational and medical use in many states but also increasing in acceptance, clinical neurologists should nevertheless recognize its relevance and seek to learn about the benefits and adverse effects of marijuana products in their patients. Data clearly indicate that between one-quarter and half of teenagers who use recreational marijuana develop an addiction, which is particularly alarming since the brain is still developing all the way until roughly the age of ²¹. Thus, marijuana can potentially have a significant impact on alertness, self-conscious awareness, memory, and executive function in these individuals. While adults who cease use of marijuana show no progression in cognitive impairment, those under 25 may continue to have cognitive impairment after cessation. However, given the range of available delivery sources of marijuana and their varying concentrations of THC, it is difficult to quantify long-term effects.

As for medical marijuana, which has now been approved in 24 states, it has been shown to be beneficial in a number of medical and neurological disorders. Although only two therapies are approved (with a third likely on the way), many other medical marijuana products are only available at special state approved dispensaries. These products contain cannabidiol and other cannabinoids that help to lower the amount of THC. Many studies and AAN guidelines have shown benefit of medical marijuana in neurological disorders such as chronic neurogenic pain and spasticity and pain in MS.

The adverse events profile in medical marijuana is even more difficult to measure for a variety of reasons, including age of patients and the number of medications patients may be using. This leaves many questions unanswered about the future of medical marijuana. It is clear, though, that marijuana is here to stay and that clinicians need to be attuned to its effects, both positive and negative, as new research continues to shed light on its role in cognitive function and disease management. n

Ronald Devere, MD, FAAN is Director of the Alzheimer’s Disease and Memory Disorders Center in Austin, TX.

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