Delta-9-tetrahydrocannabinol (Δ9-THC), better known as THC, is the popular cannabis constituent causing psycothropic effects. This phytocannabinoid protects the plant from ultraviolet (UV) radiations, environmental stress and insect predation.
When taken orally or through inhalation, THC exerts its physiological action by mimicking endogenous cannabinoids and interacting with the cannabinoid receptors of the endocannabinoid system (ECS): it is a partial agonist of CB1 and CB2, with very high binding affinity with CB1 receptors. THC exhibits an interesting therapeutic profile and it is an effective antiemetic, anti-inflammatory agent, appetite-stimulant, capable of alleviating neuropathic pain, spasticity and other kind of symptoms. 
In the plant, THC mainly occurs in the form of tetrahydrocannabinolic acid (THCA), which can decarboxylate and convert to THC with plant ageing, sun exposure or heat treatment. Some medicinal cannabis chemovars are particularly high in THCA content and the inflorescences can be smoked, vaped, baked or extracted using various methods and different kind of solvents such as ethanol, CO2, butane, tetrafluorethane among others. Generally, the extraction procedure yields products high in THC percentages and containing also other cannabinoids and phytocomponents such as terpenes and flavonoids: the combination of cannabis phytocomponents can improve the health promoting benefits because of their synergistic action named entourage effect. 
Dronabinol , the synthetic analogue of THC, have been synthesized and FDA approved as alternative to the natural molecule. This compound is manufactured in gelatin capsules containing 2.5 mg, 5 mg or 10 mg of synthetic THC in sesame oil. This product have been created in order to standardize the THC dose assumed by patients and to create consistent therapeutic programs. It is generally prescribed as support treatment for nasuea in cancer patients and as appetite stimulant. Unlike medical cannabis inflorescences, Dronabinol can provide only limited relief for certain patients due to the lack in the formulation of other important cannabis constituents such as cannabidiol (CBD), cannabichromene (CBC), terpenes etc., which are contributing to the overall cannabis therapeutic effect. Moreover, people assuming Dronabinol can sometimes experience potent psychotropic effects in comparison to the same amount of THC present in inflorescences due to the lack of compounds such as CBD, which are capable of alleviating the intoxicating psycoactive effect of THC. Because of the oral administration route, the effects of Dronabinol last longer than when inhaling medical grade cannabis, and higher quantities of the metabolite 11-hydroxy-THC are produced, greatly increasing the incurrence and the entity of unwanted psychotropic effects.
References: Barbara Costa, On the Pharmacological Properties of Δ9-Tetrahydrocannabinol (THC). Chemistry & Biodiversity (2007), 4(8), 1664–1677. doi:10.1002/cbdv.200790146 [Journal impact factor = 2.29] [Times cited= 90]
 Ferber SG. et al. The “Entourage Effect”: Terpenes Coupled with Cannabinoids for the Treatment of Mood Disorders and Anxiety Disorders. Current Neuropharmacology. 2020;18(2):87-96. doi:10.2174/1570159X17666190903103923 [Journal impact factor = 6.47] [Times cited= 74]