What is delta-9-tetrahydrocannabinol (d9-THC)?

Author: Dipl.-Chem. Mohammad Reza Talebnasab
Editorially reviewed: 13 October 2026

Delta-9-tetrahydrocannabinol (delta-9-THC, scientifically Δ9-THC) is a plant cannabinoid substantially responsible for the intoxicating effects of many cannabis preparations. It is often simply called THC; the spellings delta9-THC and d9-THC are also used. Here, the term refers to the naturally occurring compound, not all the constituents of a cannabis plant.

In brief: THC can alter perception, memory, attention and bodily functions. At the same time, certain THC-containing medicines are used for clearly defined medical indications. Medical benefit and relevant risks are not mutually exclusive. The particular preparation, condition, population studied and quality of the evidence are decisive.

What do delta-9-THC and dronabinol mean?

‘Delta-9’ identifies the position of a double bond in the molecule, not a percentage concentration. Dronabinol is the international non-proprietary name for naturally occurring (−)-trans-Δ9-tetrahydrocannabinol. The name does not specify whether the substance was obtained from a plant or produced another way. A cannabis extract, by contrast, contains several constituents and is not equivalent to the individual molecule. EUDA: chemical classification of cannabis and THC.

An important original paper by Gaoni and Mechoulam in 1964 described the isolation and structure of an active cannabis constituent. It was a milestone in the chemical characterisation of THC. However, the history of medical cannabis use extends much further back than the modern elucidation of individual molecules. Gaoni and Mechoulam, 1964; further information: History of cannabis.

THCA and THC: how does the active substance form in the plant?

An important starting material in plant cannabinoid biosynthesis is cannabigerolic acid, or CBGA. The enzyme THCA synthase can convert it into tetrahydrocannabinolic acid (THCA). THCA is an acid precursor and is chemically distinct from neutral THC. The function of THCA synthase was elucidated partly by investigating the corresponding plant gene and enzyme. Sirikantaramas et al., 2004.

Decarboxylation converts THCA into THC while releasing carbon dioxide; heat accelerates this conversion. In simplified form, the pathway is CBGA → THCA → THC. Analyses therefore differ depending on whether they report THC, THCA or a calculated total-THC value. THCA must also not be confused with THC-COOH, a breakdown product formed during human metabolism. Wang et al., 2016: investigation of decarboxylation.

THC's effects: what happens in the endocannabinoid system?

THC affects the cannabinoid receptors CB1 and CB2, among other targets. In functional cell assays, it behaves as a partial agonist: it activates the receptor, but does not necessarily reach the maximum response of a full agonist used for comparison in the system studied. ‘Partial’ means neither ‘half as strong’ nor ‘harmless’. The measured response also depends on the cell model and signalling pathway examined. Zagzoog et al., 2020.

CB1 receptors play an important role in THC's central nervous system effects. In a controlled human study, a CB1-blocking substance reduced both the subjective high and the increase in heart rate. This supports the importance of the receptor, but does not explain every effect and risk. Receptor activity alone also does not establish successful treatment of a disease. Huestis et al., 2001. Our page on the endocannabinoid system explains the principles.

Absorption and metabolism: why can the effects vary over time?

The route into the body influences how quickly and to what extent THC appears in the blood. After oral administration, concentrations typically rise more slowly and variably than after inhalation. Their subsequent time course also differs. There are also differences between individuals and preparations. The amount taken alone therefore cannot reliably predict the same course of effects for everyone. Ohlsson et al., 1980: comparative pharmacokinetic investigation.

Metabolism produces, among other substances, 11-hydroxy-THC (11-OH-THC). This metabolite is itself pharmacologically active and can be intoxicating; not all breakdown products are therefore inactive. Several enzymes, particularly those of the cytochrome P450 family, participate in the different metabolic steps. The predominant route depends on the particular metabolic step. Lemberger et al., 1973: investigation of 11-OH-THC in humans; Yabut et al., 2024: investigation of human liver enzymes.

Medical research: which uses are supported by evidence?

An objective assessment distinguishes pure active substances, standardised extracts and THC/CBD combinations. A positive study of one medicine does not establish the same effect for all THC-containing products. Likewise, an authorised indication is not a general treatment recommendation for other symptoms.

Appetite and chemotherapy-related nausea: in the USA, certain dronabinol capsules are authorised for adults with AIDS-related loss of appetite accompanied by weight loss, and for chemotherapy-related nausea and vomiting after an inadequate response to conventional antiemetics. This describes US medicine authorisations, not general German authorisation or a recommendation for self-treatment. Current US prescribing information for dronabinol.

A 2024 randomised study also investigated a THC/CBD preparation for symptoms persisting despite prior guideline-based treatment. The defined treatment success, no vomiting or retching and no rescue medication during the 120 hours studied, was achieved more often than with placebo. This does not mean complete freedom from nausea. Sedation and dizziness occurred more frequently. The study investigated an addition to usual treatment, not cancer treatment or isolated THC. Grimison et al., 2024.

Spasticity in multiple sclerosis: Sativex is a THC/CBD-containing medicine for certain adults with moderate to severe MS-related spasticity when other antispastic medicines do not work adequately and an initial treatment trial shows a clinically significant improvement. This is symptomatic treatment, not a cure for MS. In an important study, people were selected for the controlled comparison after showing a predefined symptom improvement during four weeks of treatment with nabiximols, the active mixture in Sativex. This study design must be considered when interpreting the findings. German Summary of Product Characteristics; Novotna et al., 2011.

Pain: findings are not consistent across all conditions and preparations. For example, a study involving 240 MS patients showed no statistically significant pain advantage of dronabinol over placebo. Schimrigk et al., 2017.

As of October 2026, Exilby must also be considered: a specific THC-containing cannabis flower extract used as monotherapy for chronic lower back pain with a radicular, or neuropathic, component in adults after inadequate efficacy or intolerance of non-opioid analgesics. The phase III study involving 820 adults showed an average advantage over placebo of 0.6 points on a 0–10 pain scale after twelve weeks. Adverse events were more frequent; the primary endpoint of the subsequent randomised withdrawal phase was not met. Exilby Summary of Product Characteristics; Original study, 2025.

The German additional-benefit assessment procedure began on 1 September 2026 and was not complete as of the editorial review date. Marketing authorisation and assessment of additional benefit are different procedures. These findings cannot be extrapolated to arbitrary ‘full-spectrum’ products. Federal Joint Committee: ongoing procedure.

What risks and adverse effects does THC have?

Acute psychological and cognitive effects: THC can impair attention, memory and perception, and cause anxiety and temporary psychosis-like symptoms. Controlled experiments in healthy adults substantiate such acute changes. However, temporary experimentally induced symptoms are not equivalent to having developed persistent schizophrenia. D’Souza et al., 2004.

Longer-term risks: a large international case–control study found an association between frequent, particularly daily, use of high-potency cannabis and the occurrence of a first episode of psychosis. As an observational study, it cannot provide a certain prediction for an individual and is not directly equivalent to controlled medicinal treatment. Di Forti et al., 2019: EU-GEI study.

Circulation, tolerance and dependence: THC-containing medicines can cause dizziness and changes in heart rate and blood pressure, among other effects. Repeated use can lead to tolerance and dependence; a medical purpose does not eliminate these risks. Pregnancy, breastfeeding, pre-existing psychiatric conditions and severe cardiovascular disease require particular attention to the relevant contraindications and warnings. The Exilby product information also notes that maintenance of the long-term analgesic effect has not been established. Medicine-specific safety information.

THC and medicines: what interactions are possible?

Altered metabolism: medicines that inhibit involved enzymes such as CYP2C9 or CYP3A4, or increase their activity, can change the body's exposure to THC and its metabolites. In a human study, the enzyme inhibitor ketoconazole increased exposure after a THC/CBD spray, while the enzyme inducer rifampicin reduced it. Such changes can affect effects and tolerability. Stott et al., 2013; Dronabinol prescribing information, interactions.

The reverse claim, ‘THC always inhibits the breakdown of other medicines’, would be too sweeping. In an investigation involving 18 healthy adults, the THC extract tested without CBD did not detectably inhibit the five CYP systems investigated under the single-dose conditions tested. The CBD/THC combination, by contrast, affected several of these systems. This establishes neither universal enzyme inhibition by THC nor general freedom from interactions. Bansal et al., 2023.

Additive effects: alcohol and medicines that depress the central nervous system, such as certain sleeping medicines or opioids, can increase drowsiness and coordination problems. This does not require enzyme inhibition. Combined use should be assessed by a doctor or pharmacist; do not stop or change the dose of prescribed medicines yourself. Sativex product information. More information: Cannabinoids and medicines: interactions.

THC, CBD and CBN: similar names, different effects

Cannabidiol (CBD) is a different active substance and is not a reliable antidote to THC. A controlled investigation even showed higher THC exposure and stronger adverse effects with a particular orally administered CBD/THC combination than with THC alone. The result applies to the conditions studied and does not mean that every combination has identical effects. Zamarripa et al., 2023.

Cannabinol (CBN) can form through the breakdown and oxidation of THC. Light, temperature and storage affect the composition of cannabis samples. However, this does not establish a health benefit of aged products. Zamengo et al., 2019. Other chemically distinct compounds include cannabigerol (CBG) and cannabichromene (CBC).

What do THC values mean for safety and legal status?

An analytical report should identify the sample tested, whether THC and THCA were measured separately, and the applicable detection and quantification limits. A result of ‘not detectable’ does not automatically mean the absolute absence of every single molecule. A percentage alone replaces neither a safety assessment nor a legal review of the finished product.

In Germany, medical cannabis, including dronabinol, is subject to specific requirements for medical prescribing and dispensing through pharmacies. A low THC content alone, by contrast, establishes neither the general lawfulness of marketing a cannabis product nor its suitability as a medicine. MedCanG Section 2; MedCanG Section 3; KCanG.

Fitness to drive: THC can impair driving safety. In a randomised investigation, both THC-containing and THC/CBD-containing cannabis worsened lane keeping. CBD did not reliably counteract this impairment. Neither feeling sober nor a general waiting period guarantees safe driving. Individual study time points do not provide a general clearance to drive. Arkell et al., 2020.

Conclusion: assess THC with nuance and reference to sources

Delta-9-THC is a well-studied, biologically active and intoxicating plant constituent. Clinical evidence exists for certain medicines and indications; at the same time, there are relevant risks and possible interactions. The informative question is therefore not simply ‘Is THC good or bad?’, but which statement is supported for which preparation under which conditions.

Note: this article provides general scientific information. It does not replace individual medical or legal advice and contains no dosage or use recommendations. The clinical studies mentioned did not investigate Parmorcan® shop products. Findings for medicines do not constitute efficacy promises for those products. Sources are linked directly alongside the respective statements.