Psychiatrists and other behavioral health professionals need to better understand the relationship between cannabis and mental disorders so that they can respond to increasing medical and recreational marijuana use among their patients. More than half of states now allow for medical use, and 8 states and the District of Columbia have legalized adult personal or recreational use.
Knowledge about herbal cannabis, the endocannabinoid system, and cannabinoid pharmacology is rapidly expanding. However, compared with the literature on non-medical cannabis use, the scientific literature on therapeutic use of cannabis is underdeveloped, as noted in a recent systematic review of medical cannabis and mental health.1 Although herbal cannabis has a long history of medicinal use, its federal prohibition under the Controlled Substances Act of 1970 with Drug Enforcement Administration Schedule I status has focused the federally supported cannabis research agenda for half a century on the potential harms rather than on the historically acknowledged therapeutic benefits of this complex plant.
Medicinal potential of cannabis
For the sake of this discussion, herbal cannabis refers to plant material derived from the flowering tops of Cannabis indica, sativa, or ruderalis biotypes. Indica, sativa, and indica-sativa hybrid strains are commonly available on the medicinal cannabis market.
Herbal cannabis is biochemically rich in a variety of compounds, both psychoactive and non-psychoactive. It has been reported that there are 483 compounds unique to marijuana, including more than 60 cannabinoids and some 140 terpenes. The phytocannabinoid that produces much of the psychoactive effect is delta-9-tetrahydrocannabinol (THC). However, there is increasing interest in another constituent, cannabidiol (CBD), which is not considered psychoactive but appears to have therapeutic value for a wide variety of conditions, either alone or in combination with THC.
Although federal policy has disallowed access to cannabis even for medicinal use since the passage of the Controlled Substances Act, THC was approved in a synthetically manufactured formulation in 1985 as an oral medication indicated for nausea and vomiting associated with chemotherapy. Originally a Schedule II medication, molecular THC was later reclassified under Schedule III, which indicates lower abuse potential. From the late 1970s into the early 1990s, a few patients gained access to herbal cannabis through the federal Investigational New Drug program, but no new patients were enrolled after 1992.
It is ironic that currently in the US the non-psychoactive compound CBD is generally accessible for medicinal use only in the form of federally prohibited herbal cannabis products available under state medical marijuana laws. Grant and colleagues2 have summarized succinctly a point made by many others: “Based on evidence currently available the Schedule 1 classification is not tenable; it is not accurate that cannabis has no medical value, or that information on safety is lacking.” Interestingly, the US government has held a patent on substituted CBD derivatives as antioxidants and neuroprotectants for nearly 2 decades.
Perceived benefits of medical cannabis
Regardless of the legal status of cannabis, many patients with psychiatric disorders use cannabis and report improvement in their symptoms. Patients use cannabis for symptoms of PTSD, anxiety disorders, depression, ADHD, bipolar disorder, chronic pain, insomnia, opiate dependence, and even schizophrenia. In addition, patients use cannabis for neurological conditions such as the spasticity of multiple sclerosis, agitation in dementia, and specific seizure disorders that are unresponsive to standard therapies. Patients also use cannabis to reduce the nausea and anorexia of cancer chemotherapies and to improve their mood and outlook—frequently with their oncologist’s approval.
With the advent of state medical cannabis laws beginning with California in 1996, medical cannabis has become commercially available in many states as herbal material that may be smoked or vaporized, as well as consumed in a wide variety of other preparations. In addition to the various formulations available through state-based programs, pharmaceutical-grade whole herbal cannabis extracts have been under development during the past 2 decades. The first product to gain approval for medical use was Sativex, a whole herbal extract standardized to a THC:CBD ratio of 1:1 and administered as a sublingual spray. Sativex was approved in Canada for use in multiple sclerosis in 2005 and chronic cancer pain in 2006, and has been approved for medical use in at least 2 dozen countries, although it is not FDA approved. More recently, a liquid formulation of pure plant-derived CBD (Epidiolex) has been undergoing trials as an anticonvulsant for seizures refractory to other available treatments.