Δ-8-Tetrahydrocannabinol

Δ-8-tetrahydrocannabinol (delta-8-THC, Δ8-THC) is a psychoactive cannabinoid found in the Cannabis plant. It is an isomer of delta-9-tetrahydrocannabinol (delta-9-THC, Δ9-THC), the compound commonly known as THC, with which it co-occurs in hemp; natural quantities of ∆8-THC found in hemp are low.

Psychoactive effects are similar to that of Δ9-THC, with central effects occurring by binding to cannabinoid receptors found in various regions of the brain. During the production process of converting cannabidiol extracted from hemp to ∆8-THC, toxic chemical reagents are used, which can contaminate the product. In the US, ∆8-THC products are neither mandatorily tested nor FDA approved, hence concern has been raised about their safety. In addition, as of 2022, the safety profile of regular, long-term delta-8-THC consumption is unknown.

Partial synthesis of ∆8-THC was published in 1941 by Roger Adams and colleagues at the University of Illinois. After the 2018 United States farm bill was signed, ∆8-THC products partially synthesized from compliant sources (including industrial hemp and derivative cannabidiol extracts) experienced a rise in popularity; THC products have been sold in licensed, regulated recreational cannabis and medical cannabis industries within the United States only in California, Pennsylvania, and regulated in Michigan and Oregon. According to a March 2024 study, 11% of US twelfth graders have used ∆8-THC over the past 12 months.

Effects
∆8-THC is moderately less potent than Δ9-THC. This means that while its effects are similar to that of Δ9-THC, it would take more ∆8-THC to achieve a comparable level of effect.

A 1973 study testing the effects of ∆8-THC in dogs and monkeys reported that a single oral dose of 9,000 milligrams per kilogram of body mass (mg/kg) was nonlethal in all dogs and monkeys studied. The same study reported that the median lethal dose of ∆8-THC in rats was comparable to that of ∆9-THC. Both isomers of THC have been found to cause a transient increase in blood pressure in rats, although the effects of cannabinoids on the cardiovascular system are complex. Animal studies indicate that ∆8-THC exerts many of its central effects by binding to cannabinoid receptors found in various regions of the brain, including the cerebral cortex, thalamus, basal ganglia, hippocampus, and cerebellum.

Production
∆8-THC is typically synthesized from cannabidiol extracted from hemp, as the natural quantities of ∆8-THC found in hemp are low. This is called semisynthesis or partial synthesis. The reaction often yields a mixture that contains other cannabinoids and unknown reaction by-products. As a result, most products sold as ∆8-THC are not actually pure ∆8-THC. Little is known about the identity and the health effects of the impurities. Some manufacturers of ∆8-THC may use household chemicals in the synthesis process, potentially introducing harmful contaminants. In that sense, ∆8-THC can be called a "semisynthetic phytocannabinoid" or semisynthetic endocannabinoid, as it is obtained by (partial) chemical synthesis. It is not to be confused with the term synthetic cannabinoid, however.

Safety
As of 2022, the safety profile, including risks of psychosis and addiction after regular, long-term delta-8-THC use was unknown.

As of 2022, there have been at least 104 adverse event reports made regarding ∆8-THC, and at least two deaths associated with ∆8-THC products. US national poison control centers received 2,362 exposure cases of delta-8 THC products between January 1, 2021, and February 28, 2022; 58% of these exposures involved adults, and 70% thought they required medical care.

Mechanism of action
The pharmacodynamic profile of ∆8-THC is similar to that of ∆9-THC. It is a partial agonist of CB1 and CB2 cannabinoid receptors with about half the potency of ∆9-THC in most but not all measures of biological activity. ∆8-THC has been reported to have a Ki value of 44 ± 12 nM at the CB1 receptor and 44 ± 17 nM at the CB2 receptor. These values are higher than those typically reported for ∆9-THC (CB1 Ki = 40.7 nM) at the same receptors, indicating that ∆8-THC binds to cannabinoid receptors less efficiently than ∆9-THC.

Pharmacokinetics
The pharmacokinetic profile of ∆8-THC is also similar to that of ∆9-THC. Following ingestion in humans, hepatic cytochrome P450 enzymes including CYP2C9 and CYP3A4 first convert ∆8-THC into 11-hydroxy-Δ8-tetrahydrocannabinol (11-OH-Δ8-THC). Next, dehydrogenase enzymes convert 11-OH-Δ8-THC into 11-nor-Δ8-tetrahydrocannabinol-9-carboxylic acid (11-nor-Δ8-THC-9-COOH, also known as Δ8-THC-11-oic acid). Finally, Δ8-THC-11-oic acid undergoes glucuronidation by glucuronidase enzymes to form 11-nor-Δ8-tetrahydrocannabinol-9-carboxylic acid glucuronide (Δ8-THC-COOH-glu), which is then excreted in the urine.

Physical and chemical properties
∆8-THC is a tricyclic terpenoid. Although it has the same chemical formula as ∆9-THC, one of its carbon-carbon double bonds is located in a different position. In ∆8-THC, the double bond is between the eighth and ninth carbons in structure, while in Δ9-THC, the double bond is between the ninth and tenth carbons in structure. This difference in structure increases the chemical stability of ∆8-THC relative to ∆9-THC, lengthening shelf life and allowing the compound to resist undergoing oxidation to cannabinol over time. Like other cannabinoids, ∆8-THC is very lipophilic (log P = 7.4 ). It is an extremely viscous, colorless oil at room temperature.

While ∆8-THC is naturally found in plants of the Cannabis genus, this compound can also be produced in an industrial or laboratory setting by exposing CBD to acids and heat. Solvents that may be used during this process include methylene chloride, toluene, and hexane. Various Brønsted or Lewis acids that may be used to facilitate this isomerization include tosylic acid, indium(III) triflate, trimethylsilyl trifluoromethanesulfonate, hydrochloric acid, and sulfuric acid. Because it is possible for chemical contaminants to be generated during the process of converting CBD to ∆8-THC, such as Δ10-THC, 9-OH-HHC and other side products, as well as the potentially toxic chemical reagents used during manufacture, concern has been raised about the safety of untested or impure ∆8-THC products.

The ongoing controversy regarding the legal status of ∆8-THC in the U.S. is complicated by chemical nomenclature. According to a 2019 literature review published in Clinical Toxicology, the term synthetic cannabinoid typically refers to a full agonist of CB1 and CB2 cannabinoid receptors. According to the review, the following is stated:

"'The psychoactive (and probably the toxic) effects of synthetic cannabinoid receptor agonists are likely due to their action as full receptor agonists and their greater potency at CB1 receptors.'"

However, ∆8-THC and ∆9-THC are partial agonists of cannabinoid receptors. They are less potent and less toxic than many synthetic cannabinoids. It has not been definitively proven if full agonism is the reason for toxicity since ∆9-THC has been shown to act as a full CB1 agonist on specific CB1 receptors located in the hippocampus section of the brain. Furthermore, the synthetic cannabinoid EG-018 acts as a partial agonist. The classical cannabinoid structure is that of a dibenzopyran structure. This group includes THC. THC interacts with a different spot inside of the CB1 receptor than synthetic cannabinoid such JWH-018. This may explain the latter's toxicity.

History
The partial synthesis of ∆8-THC was published in 1941 by Roger Adams and colleagues at the University of Illinois. In 1942, the same research group studied its physiological and psychoactive effects after oral dosing in human volunteers. Total syntheses of ∆8-THC were achieved by 1965. In 1966, the chemical structure of ∆8-THC isolated from cannabis was characterized using modern methods by Richard L. Hively, William A. Mosher, and Friedrich W. Hoffmann at the University of Delaware. A stereospecific synthesis of ∆8-THC from olivetol and verbenol was reported by Raphael Mechoulam and colleagues at the Weizmann Institute of Science in 1967. ∆8-THC was often referred to as "Delta-6-THC" (Δ6-THC) in early scientific literature, but this name is no longer conventional among most authors.

Federal laws
In 1937, ∆9-THC was effectively made illegal with the passage of the (since-repealed) Marihuana Tax Act, which made growing cannabis require a tax stamp. President Ronald Reagan re-enacted mandatory sentences for cannabis-related offenses. As of 1 September 2023, 24 states have legalized cannabis, with others having reduced penalties.

The 2018 United States farm bill, signed into law in December 2018, states the following:

"'The term hemp means the plant Cannabis sativa L. and any part of that plant, including the seeds thereof and all derivatives, extracts, cannabinoids, isomers, acids, salts, and salts of isomers, whether growing or not, with a delta-9 tetrahydrocannabinol concentration of not more than 0.3 percent on a dry weight basis.'"

Despite claims of legality by manufacturers, independent testing of products from retail has often revealed significant levels of ∆9-THC. Many of these levels are well above one legal threshold.

In October 2020, the DEA Interim Final Rule addressed synthetic cannabinoids. Some believed that this also applied to ∆8-THC products and other hemp derivatives allowed by the Farm Bill.

FDA
∆8-THC has not been evaluated or approved by the FDA. Consequently, Δ-8-tetrahydrocannabinol is not recognized under the Federal Food, Drug, and Cosmetic Act as safe and effective for any use. The FDA has taken action against businesses that have illegally marketed ∆8-THC for therapeutic use. The FDA has also taken action against businesses that sold ∆8-THC in forms that closely resemble (typically non-psychoactive) food products such as chips or cookies.

Individual states
While most states have not arrested significant numbers of people for ∆8-THC, a handful have been arrested and charged, leading to confusion as to its legal status in those states.

In 2021, one store owner in Menomonee Falls, Wisconsin was facing a sentence of up to 50 years for allegedly selling ∆8-THC products with illegal amounts of ∆9-THC. Other raids and arrests have happened due to the ∆9-THC content of these products in North Carolina, and Texas, among other places. In 2022, Catoosa County, Georgia Sheriff Sisk announced to prosecute stores distributing ∆8-THC with non-compliant ∆9-THC levels: "The products the sheriffs office has purchased and tested all contain significant levels of ∆9. [We have the] evidence needed to move forward with prosecution and seizures." There are also issues related to incidental manufacture of ∆9 THC, as ∆9 is produced as an intermediate product in the process of acid catalyzed ring closure of cannabidiol.

There are multiple court decisions pertaining to the legality of Delta-8 THC. AK Futures LLC vs Boyd Street Distro, LLC (2022) was one of the earliest decisions made in a federal court, stating "On the available record, the delta-8 THC in AK Futures’ e-cigarette liquid appears to fit comfortably within the statutory definition of “hemp.”". United States vs. Rice, however, came to the opposite conclusion, "In short, Delta-8 remains a controlled substance. Although Delta-10 was not directly referenced in the DEA’s letter, there is no basis (in the record before the court) to believe that the DEA will treat Delta-10 in a different manner.". United States vs. Plancarte also states, "There is no legal D9-THC threshold for synthetic derivatives of THC. A gray area is whether Delta-8 THC is legal; it probably is when it occurs naturally in hemp, but this is not clear."

∆8-THC products have been sold in licensed, regulated recreational cannabis and medical cannabis industries within the United States including California and Pennsylvania's licensed, regulated medical cannabis system since 2020. Both Michigan and the state of Oregon have regulated Delta-8-THC products sold under their regulated cannabis system.

Products and prevalence of use
Common Delta-8 products range from bulk quantities of unrefined distillate to prepared cannabis edibles and atomizer cartridges. In the US, they are usually marketed as federally legal alternatives to their ∆9-THC counterparts.

∆8-THC products partially synthesized from compliant sources (including industrial hemp and derivative cannabidiol extracts) experienced a rise in popularity in the US following the passage of the 2018 Farm Bill. This led to it being sold by a diverse range of retailers, including head shops, smoke shops, vape shops, dispensaries, gas stations, and convenience stores.

In March 2024, a study of self-reported prevalence of Δ8-THC use among US twelfth graders was published: Of those reporting Δ8-THC use, 35% had used it at least 10 times in the past 12 months. Consumption was lower in Western than Southern and in states, where Δ8-THC was regulated versus not regulated.

Research
Although it is a minor constituent of medical cannabis, no large clinical studies have been conducted on delta-8-THC alone as of 2022. One study (ongoing as of November 2023) is focused on determining the degree of pharmacologic and pharmacokinetic similarity between ∆8-THC and ∆9-THC.