CB1 — the central cannabinoid receptor

TL;DR

• GPCR, primarily in the CNS (basal ganglia, hippocampus, cerebellum).
• Presynaptic — inhibits neurotransmitter release.
• THC is a partial agonist → psychoactive effect.
• CB1 antagonists (rimonabant) were withdrawn for depression.

Where is CB1 located?

Highest density: basal ganglia, hippocampus, cerebellum, cortex — consistent with motor, memory and cognitive effects (Zou & Kumar 2018). In the periphery CB1 sits in adipose, liver and muscle tissue and modulates energy homeostasis (Lu & Mackie 2016).

How does THC act at CB1?

Δ9-THC is a partial agonist at CB1 (Ki ≈ 40 nM). Via Gi/o: inhibits adenylyl cyclase, closes voltage-gated Ca²⁺ channels, opens K⁺ — net: reduced presynaptic release (Pertwee 2015).

Physiological regulation and synaptic plasticity

The CB1 receptor controls synaptic transmission through an extraordinary mechanism, so-called retrograde signal transcription. Unlike classical neurotransmitters, endocannabinoids such as anandamide and 2-AG are synthesized on demand in the postsynaptic membrane. They travel backward through the synaptic cleft to bind to presynaptic CB1 receptors. This activation leads to a temporary or permanent reduction in the release of neurotransmitters such as glutamate or gamma-aminobutyric acid. In this way, the system acts as a cellular brake, preventing neuronal overexcitation and precisely regulating balance in the nervous system.

This retrograde inhibition is of central importance for synaptic plasticity, which forms the basis for learning processes and memory formation. By modulating transmitter release, the CB1 receptor influences both short-term and long-term synaptic depression. This adaptability allows the brain to flexibly adjust neuronal networks to new stimuli. Dysregulation of this finely tuned system is associated with various neurological disorders. Research into these mechanisms highlights why targeting the receptor generates such great therapeutic interest, as it directly intervenes in the body's own information processing.

• Retrograde signaling from the postsynaptic to the presynaptic region
• On-demand synthesis of the endogenous ligands anandamide and 2-AG
• Modulation of excitatory and inhibitory neurotransmitters
• Key role in synaptic plasticity and cellular learning processes

Therapeutic potential and medical application in Switzerland

In Switzerland, the medical application of cannabinoids targeting the CB1 receptor has changed fundamentally. Since August 2022, medical cannabis can be prescribed directly by doctors without a time-consuming exceptional permit from the Federal Office of Public Health (FOPH). This legal facilitation enables faster access to therapies for patients with chronic conditions. Prescriptions are filled through Swiss pharmacies, which dispense magistral formulas or approved medicinal products. The monitoring of the quality and safety of these preparations is the responsibility of the therapeutic products agency Swissmedic, ensuring controlled treatment.

The targeted activation of the CB1 receptor is used in medical practice primarily to relieve chronic pain, spasticity in multiple sclerosis, and therapy-resistant nausea. Since the activation of the receptor in the central nervous system is also responsible for the psychoactive effects, the therapy requires careful dose titration. Medical professionals usually rely on a gradual dose escalation to achieve the desired therapeutic effect while minimizing undesirable side effects. Current evidence shows that combination products containing THC and CBD in particular enable a balanced activation of the receptor and can improve tolerability in everyday life.

• Direct medical prescribability in Switzerland since August 2022
• Removal of the BAG exceptional permit for medical applications
• Therapeutic focus on chronic pain and muscle spasticity
• Careful dosing to avoid undesirable psychoactive effects

Toxicological relevance and road safety

With regular and intensive intake of exogenous agonists such as THC, the endocannabinoid system responds with adaptive measures at the CB1 receptor. To prevent chronic overstimulation, receptor internalization occurs. During this process, the receptor proteins are translocated from the cell surface to the cell interior and are temporarily no longer available for signal transmission. This process, also known as downregulation, clinically leads to the development of tolerance, meaning that higher doses are required to achieve the same effect. However, after a period of abstinence, this mechanism is reversible, and receptor density on the cell membrane returns to normal.

The modulation of the CB1 receptor has direct consequences for fitness to drive and the legal situation in Swiss road traffic. Since the activation of the receptor impairs cognitive functions and motor coordination, a strict zero-tolerance policy applies in Switzerland. The legal limit for the detection of THC in the blood is a mere 1.5 micrograms per litre. Exceeding this limit inevitably leads to a determination of unfitness to drive and entails administrative and criminal consequences. Consumers must be aware that, due to its lipophilicity, THC remains detectable in the body long after the perceptible effects have subsided.

• Receptor downregulation through internalization during chronic consumption
• Reversible tolerance development after cessation of intake
• Strict Swiss limit of 1.5 micrograms of THC per litre of blood
• Impairment of motor and cognitive abilities in road traffic

FAQ