Almost all literature cites that THC was first discovered in 1964 by Israeli chemist Rafael Mechoulam, who first isolated THC in Lebanese hashish, which I cannot dispute. Dr. Mechoulam was also responsible for discovering (and naming) Anandamide, which is a very critical endocannabinoid that our bodies make naturally. However, it's worth pointing out that this detailed article claims an American doctor by the name of Roger Adams discovered THC in 1940 and the research seems to have merit.
Regardless if THC was discovered in 1940 or 1964, a much larger finding happened in 1988. Dr. Allyn Howlett of Wake Forest University uncovered the binding sites for THC in the human brain. She discovered something revolutionary: THC was attaching itself to special cell sites in the hippocampus (responsible for memory), the frontal cortex (where we think), and the cerebellum (responsible for movement). In short, Dr. Howlett was able to observe THC binding to CB1-R Cannabis Receptors, which are the binding sites, or "locks", in which the THC "key" fits perfectly. This was a significant scientific discovery.
MORE RESOURCES: For more details on cannabis receptors and the Endocannabinoid System (ESC), please see the Cannabinoids Library page and my supplemental learning document How Cannabis Works as a Medicine.
THC works by essentially binding primarily to cannabinoid receptors in the brain and central nervous system. The results of introducing THC into your system can include feelings of euphoria, elation, relaxation, changes in thinking, impairment to short-term memory, pain relief, anxiety (when too much is taken), slowed perception of time, laughter, dizziness, hunger, red eyes, and mild impairment to motor skills, to name some of the effects.
Possible Therapeutic Effects
Research of THC is showing evidence that it engages the immune system to address inflammation and pain, induces appetite and sleep, increases metabolism and is very beneficial in treating cancer, its symptoms and its drug treatment side effects.
-may help to treat neurodegenerative diseases. Study 1.
-may help in treating Post Traumatic Stress Disorder (PTSD). Study 1.
-may help in treating some symptoms of Muscular Sclerosis (MS). Article 1.
-may help in treating rheumatoid arthritis.
-US government Cannabinoids Patent #6630507 as antioxidants and neuroprotectants.
As you probably know, Tetrahydrocannabinol, or THC, is the cannabinoid that is responsible for cannabis' psychoactive effects. To assert that THC is the most abundant cannabinoid in most modern cannabis strains (excluding any CBD-rich strains) is not completely accurate. THC's acid form, Tetrahydrocannabolic Acid (THCa), actually has the biggest presence in the cannabis plant.
NOTES: The formal, accurate name for THC is "trans-Delta-9-Tetrahydrocannabinol". THCv also offers a varying type of psychoactive effects.
THC is ultimately formed when its precursor acid form, THCa, is converted to its neutral form - THC. THCa is one of the three major cannabinoid branches formed by Cannabigerolic Acid (CBGa). The cannabis plant possesses natural enzymes, referred to as "synthases", that break the CBGa down and convert it to one of the major cannabinoids. As shown in the graphic below, you can see at a high level the tranformation from CBGa to THCa and then finally forming THC with the loss of a CO2 molecule via decarboxylation.