This informal CPD article ‘Understanding the strength of medical cannabis flower?’ was provided by Dr Sue Clenton, Medical Director and Specialist Consultant Oncologist at Releaf, a HealthTech company dedicated to transforming access to Cannabis Based Products for Medical use (CBPMs) in the UK.
To patients new to cannabis-based medicine, especially those totally naive to cannabis, the concept of “strength” can be a little confusing. Medical cannabis products are often described using percentages, most commonly referring to THC levels, and it is fair that patients assume that these numbers alone determine how effective a treatment might be. In reality, the situation is rather more nuanced.
The therapeutic effects of medical cannabis depend on a somewhat surprisingly wide combination of factors. The balance and range of cannabinoids present, the terpene profile, the type of cannabis-based medicine and the way it is administered, and that’s not even mentioning the fact that all patients respond differently to cannabinoid treatment. Considerations such as previous exposure to cannabis, body chemistry, underlying health conditions, and even the timing of doses can influence how a particular product feels and performs. [1] THC levels certainly contribute to the overall effects of treatment, but they do not tell the whole story.
What “strength” actually means in medical cannabis
THC, or tetrahydrocannabinol, is the cannabinoid most often associated with cannabis potency. It is responsible for the intoxicating effects of cannabis and plays an important therapeutic role in certain medical contexts, particularly in chronic pain, muscle spasticity, and appetite stimulation. [2]
CBD, or cannabidiol, behaves quite differently. It does not produce intoxicating effects, yet it has its own therapeutic properties and can influence how THC behaves in the body. In some cases, CBD may temper some of THC’s psychoactive effects while contributing benefits such as anti-inflammatory, anxiolytic, or anticonvulsant activity. [3]
However, THC and CBD are only part of the picture. The cannabis plant contains dozens of additional cannabinoids, along with aromatic compounds known as terpenes. These molecules contribute to the overall pharmacological profile of a cannabis cultivar and may subtly influence how the treatment feels and performs. [2], [4] For this reason, clinicians rarely view strength as a single number. Instead, it is better understood as the combined effect of several interacting compounds working together within a carefully prescribed treatment plan.
How strong is medical cannabis flower in the UK?
In the UK, prescribed medical cannabis flower spans a fairly broad range of THC concentrations. At the lower end, some cultivars contain almost 0% THC, while some cultivars reach above the 28% mark. Once THC levels rise above 20%, the flower is generally considered high potency.
Those figures can sound rather dramatic when seen in isolation, but in medical prescribing they function less like marketing labels and more like pharmacological reference points. Every batch of prescribed medical cannabis undergoes laboratory testing to confirm the levels of cannabinoids present. This standardisation allows clinicians to prescribe with confidence, knowing that the cannabinoid content remains consistent from one supply to the next.
This type of long-term consistency in treatment options means patients can gradually adjust their dose and learn how a particular cannabinoid profile affects their symptoms without the uncertainty that comes with unregulated ‘black market’ cannabis. [5] So while the THC percentage gives a useful indication of potential potency, it should not be mistaken for a direct measure of therapeutic value.
How specialist prescribers determine the right treatment strength
Choosing the appropriate strength of medical cannabis is not simply a matter of selecting a percentage from a list. It is a clinical decision shaped by a patient’s medical history, symptoms, and previous treatment experiences.
Doctors consider several factors when recommending a cannabinoid profile. The condition being treated is obviously important, as different symptoms respond differently to cannabinoids. Chronic pain, neurological disorders, sleep disturbance, and treatment-related side effects may all require slightly different approaches. A patient’s previous exposure to cannabis is also relevant, as individuals who are entirely new to cannabinoids can be more sensitive to THC.
For this reason, treatment often begins cautiously. The majority of prescribing clinicians prefer to start with lower THC concentrations and adjust gradually over time, a process known as titration. This allows patients to find a level that relieves symptoms without producing unnecessary/unwanted side effects. Follow-up consultations are a key part of this process. As doctors and patients observe how symptoms respond, treatment plans can be refined. The goal is not maximum potency, but the most effective balance between symptom relief and day-to-day functioning.
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References
- Lu HC, Mackie K. An introduction to the endogenous cannabinoid system. Biol Psychiatry Cogn Neurosci Neuroimaging. 2021;6(6):607–615.
https://pubmed.ncbi.nlm.nih.gov/26698193/ - Pertwee RG. Cannabinoid pharmacology: the first 66 years. Br J Pharmacol. 2006;147(S1):S163–S171.
https://pubmed.ncbi.nlm.nih.gov/16402100/ - Ibeas Bih C, Chen T, Nunn AVW, Bazelot M, Dallas M, Whalley BJ. Molecular targets of cannabidiol in neurological disorders. Neurotherapeutics. 2015;12(4):699–730.
https://pubmed.ncbi.nlm.nih.gov/26264914/ - Russo EB. Taming THC: potential cannabis synergy and phytocannabinoid-terpenoid entourage effects. Br J Pharmacol. 2011;163(7):1344–1364.
https://bpspubs.onlinelibrary.wiley.com/doi/10.1111/j.1476-5381.2011.01238.x - NICE. Cannabis-based medicinal products. NICE guideline NG144. 2019.
https://www.nice.org.uk/guidance/ng144
