Cannabinoids and Terpenes — UK Medical Cannabis Guide

Medical cannabis is not a single substance. A licensed product may contain dozens of naturally occurring compounds — cannabinoids, terpenes, flavonoids — each with distinct physiological effects. Understanding what your prescription contains, and how these compounds interact, helps you have more informed conversations with your prescriber and manage your treatment more effectively.

The Main Cannabinoids

THC (Tetrahydrocannabinol)

THC is the primary psychoactive compound in cannabis. It acts as a partial agonist at CB1 receptors throughout the central and peripheral nervous system. Clinical effects include analgesia (pain reduction), muscle relaxation, appetite stimulation, and modulation of nausea. At higher doses, THC can cause anxiety, paranoia, and — in vulnerable individuals — psychotic episodes. This is why UK prescribers start at low doses and titrate upward slowly. In UK medical cannabis products, THC content is clearly stated on the label as a percentage of dry weight (for flower) or as mg/ml (for oils).

CBD (Cannabidiol)

CBD is non-psychoactive — it does not produce intoxication and does not bind directly to CB1 receptors. It modulates the endocannabinoid system through multiple indirect pathways. Clinical properties include anxiolytic effects, anticonvulsant activity (the basis for Epidyolex, the NHS-licensed cannabis-derived medicine for epilepsy in patients aged 2 and over with Dravet syndrome and Lennox-Gastaut syndrome), anti-inflammatory action, and some analgesic effect. CBD is frequently described as moderating the effects of THC — it may reduce THC-induced anxiety and paranoia when present alongside it.

CBG (Cannabigerol)

CBG is the biosynthetic precursor to both THC and CBD — often described as the "mother cannabinoid." It is typically present in small amounts in mature cannabis plants. Early research suggests anti-inflammatory, antibacterial, and neuroprotective properties. CBG does not produce intoxication. It is increasingly present in some UK licensed products, but clinical evidence in humans remains limited. Your prescriber may mention it in the context of broad-spectrum formulations.

CBN (Cannabinol)

CBN is a degradation product of THC, forming as cannabis ages and THC oxidises. It has mild sedative properties and may contribute to the sleep-promoting effects of aged cannabis products. Some UK-licensed products marketed for sleep contain elevated CBN. Evidence in humans is preliminary, but CBN is generally considered non-intoxicating at typical doses. If you have been prescribed a sleep-focused product, CBN may feature in its profile.

The Entourage Effect

The entourage effect is the hypothesis — supported by a growing body of preclinical evidence — that the compounds in cannabis work together more effectively than any single compound in isolation. THC and CBD combinations show different clinical profiles than THC alone. Terpenes may modulate the effects of cannabinoids. Whole-plant or broad-spectrum products may therefore perform differently from isolates (pure THC or pure CBD). Most UK medical cannabis prescriptions involve whole-plant or broad-spectrum products rather than isolates, partly on the basis of the entourage effect hypothesis and partly because the clinical evidence for whole-plant products is often stronger in specific conditions.

Terpenes: What They Are and What They Do

Terpenes are aromatic compounds found throughout the plant kingdom — they give cannabis its characteristic smell, and each strain's distinct aroma reflects its terpene profile. In cannabis, terpenes are increasingly understood to have physiological effects of their own and to interact with cannabinoids.

The most clinically relevant terpenes in UK medical cannabis products:

• Myrcene: The most abundant terpene in most cannabis strains. Associated with sedative, relaxing effects. Often dominant in products prescribed for sleep and pain. Responsible for the earthy, musky aroma of many cannabis flower products.
• Limonene: Citrus-scented; associated with mood elevation, stress reduction, and potential anti-anxiety effects. Found in products used for anxiety and low mood. May have anti-inflammatory properties.
• Alpha- and Beta-Pinene: Pine-scented; associated with alertness, focus, and bronchodilation. May counteract some of the short-term memory impairment associated with THC. Found in daytime or functional products.
• Beta-Caryophyllene: Spicy, peppery aroma. Uniquely among terpenes, it binds directly to CB2 receptors and has established anti-inflammatory and analgesic effects. Found in many pain-focused products. The only terpene currently considered a dietary cannabinoid.
• Linalool: Floral, lavender-like scent. Anxiolytic and sedative properties. Often present in products for anxiety and sleep.

THC:CBD Ratios — What They Mean

UK prescriptions are frequently described by their THC:CBD ratio. Understanding what these ratios mean in practice helps you understand what you have been prescribed:

• High CBD (e.g. 1:20 THC:CBD or CBD-only): Very low intoxication risk. Suitable for daytime use, anxiety-focused treatment, patients sensitive to THC, or those new to medical cannabis. Common first prescription for many conditions.
• Balanced (1:1 THC:CBD): Moderate effects. THC provides analgesic benefit; CBD moderates potential adverse effects. Common for chronic pain, sleep, and PTSD management.
• High THC (predominantly THC): Stronger psychoactive effect. Used in specific presentations — severe pain, chemotherapy-induced nausea, some PTSD night-time prescriptions. Typically started at very low doses.

Flower vs Oil — A Brief Reference

The same cannabinoid and terpene profiles are found in both flower and oil products, but the delivery method significantly affects onset time and duration of effect. For a detailed comparison including administration methods, see our dedicated flower vs oil guide.

Reading Your UK Prescription Label

UK medical cannabis products from licensed pharmacies carry standardised labelling. Key information to look for: product name and batch number; THC percentage (% by weight for flower; mg/ml for oils); CBD percentage or mg/ml; dominant terpene profile (increasingly common on higher-quality products); dosing instructions from your prescriber; storage requirements and expiry date. If your product's cannabinoid or terpene profile is not what you expected based on your consultation, contact your pharmacy or clinic before using it.