Cannabis has been used medicinally for thousands of years, long before physicians understood receptors, neurotransmitters, inflammatory pathways or the complex chemistry of the human nervous system. Ancient healers could not explain the plant in molecular terms, but generations of observation led different cultures to incorporate cannabis preparations into treatments for pain, digestive complaints and other ailments.
Modern science has provided a clearer picture of why cannabis produces such wide-ranging effects. The plant contains hundreds of chemical compounds, including cannabinoids, terpenes, flavonoids and other biologically active substances. Among the best known are tetrahydrocannabinol, or THC, cannabidiol, or CBD, and cannabigerol, commonly called CBG.
Much of the scientific interest surrounding cannabis centers on the endocannabinoid system, a signaling network involved in regulating numerous physiological processes. The system includes cannabinoid receptors, naturally produced endocannabinoids and enzymes responsible for their production and breakdown. It has roles in pain processing, appetite, memory, mood, immune activity and other functions associated with maintaining physiological balance.
CB1 receptors are found extensively throughout the central nervous system, while CB2 receptors are associated largely with immune tissues and cells, although the biology of both receptor types is considerably more complex than those descriptions alone suggest. THC can activate cannabinoid receptors, particularly CB1, producing many of cannabis’s characteristic psychoactive and physiological effects. CBD works differently and has a more indirect and complicated relationship with the endocannabinoid system.
Cannabis also contains aromatic compounds known as terpenes. Myrcene, limonene and beta-caryophyllene are among those frequently discussed in cannabis research. Beta-caryophyllene is particularly interesting because it can interact with CB2 receptors, making it unusual among common plant terpenes. Researchers continue investigating whether terpenes contribute independently or collectively to the therapeutic effects associated with different cannabis preparations.
The evidence surrounding individual terpenes, however, remains incomplete. Laboratory findings and traditional experience have generated considerable interest in their potential anti-inflammatory, antimicrobial, calming and other biological properties, but findings from laboratory experiments cannot automatically be translated into established treatments in humans. Claims that a particular terpene reliably produces sedation, improves mood or treats infection require considerably more clinical evidence.
Cannabis contains flavonoids and phenolic compounds as well. These substances have attracted scientific attention for antioxidant, anti-inflammatory and other possible biological activities. Some compounds found in cannabis have demonstrated antimicrobial activity under laboratory conditions, adding another area of research to a plant already known for unusually complicated chemistry.
Historical claims involving cannabis and parasites require similar caution. Cannabis has appeared in traditional medical practices for gastrointestinal ailments, and laboratory researchers have explored antimicrobial and antiparasitic properties of cannabinoids, terpenes and related plant compounds. However, evidence does not establish cannabis as a reliable treatment for human parasitic infections. Laboratory observations involving cellular membranes or microorganisms should not be interpreted as proof that consuming cannabis can eliminate parasites or cure an infection in the human body.
Traditional medicinal use can provide scientists with valuable clues without, by itself, establishing clinical effectiveness. Ancient healers worked through observation and accumulated experience rather than controlled trials, standardized doses and laboratory analysis. Some traditional remedies have subsequently produced medically valuable compounds, while others have failed when subjected to rigorous testing. Cannabis occupies an unusual position because thousands of years of traditional use are now being examined through modern pharmacology.
Its effects on consciousness also contributed to cannabis becoming part of spiritual, religious and ceremonial traditions in several cultures. CB1 receptors are heavily represented in areas of the brain involved in memory, cognition, emotion, movement and perception. THC’s interaction with these receptors can alter sensory perception, attention, short-term memory and emotional experience.
Those effects can be experienced very differently from one person to another. Some users report relaxation or changes in perspective, while others can experience anxiety, impaired coordination, confusion or other unwanted effects, particularly with larger amounts of THC. The experience also varies according to dose, potency, method of consumption, cannabinoid composition, individual physiology and previous exposure.
Cannabis remained part of Western medicine well into the modern era. During the nineteenth and early twentieth centuries, cannabis extracts and tinctures were sold and prescribed for various conditions in the United States and Europe. Cannabis preparations were included in the United States Pharmacopeia during a period when plant-derived medicines remained an important part of medical practice.
Its eventual disappearance from conventional American medicine resulted from a complicated combination of regulatory, political, medical and social developments. Cannabis became increasingly restricted during the first half of the twentieth century, culminating decades later in its placement under federal controlled-substance law. Historical accounts continue to examine the roles played by changing medical standards, racial and political rhetoric, law enforcement, federal policy and economic interests in the development of prohibition.
That history should not be simplified into either extreme. Cannabis was not removed from widespread medical practice solely because scientists proved it therapeutically worthless, but neither does its long history establish that every medicinal claim made about the plant is scientifically valid.
Modern research has instead produced a far more detailed and sometimes complicated picture.
Cannabinoid-based medicines and cannabis-derived compounds have demonstrated legitimate medical applications in specific circumstances. Research has examined their roles in chronic pain, nausea and vomiting associated with chemotherapy, muscle spasticity, appetite, sleep and neurological disorders. Purified cannabidiol has also become an established prescription treatment for certain severe seizure disorders.
At the same time, cannabis is not biologically harmless simply because it comes from a plant. THC can impair memory, reaction time, judgment and coordination, and frequent or high-potency use carries additional risks for some people. Cannabis can also interact with medications, and inhaling combusted material introduces respiratory concerns unrelated to the cannabinoid system itself.
The scientific story of cannabis, therefore, is more compelling when neither its potential nor its limitations are exaggerated. Its chemistry clearly interacts with important biological systems, and several of its compounds have demonstrated therapeutic value. Other proposed benefits remain under investigation, while some popular claims extend considerably beyond the available evidence.
What ancient healers discovered through experience has become the subject of pharmacology, neuroscience, immunology and clinical medicine. They could observe that the plant changed pain, perception, appetite, sleep and other aspects of human experience, but they could not have known why.
Thousands of years later, researchers are beginning to answer that question compound by compound and receptor by receptor. Cannabis has traveled from traditional medicine to prohibition and back into laboratories and medical practices, carrying with it an unusually long history of human use. Modern science is no longer simply asking whether cannabis affects the body. It is determining which compounds produce which effects, at what doses, for which conditions and with what risks.
That continuing research may ultimately prove to be the most important chapter in the plant’s long medical history.