An Interview with Dr. Rowan Thompson, Prescribing Resident Doctor
The recent coverage linking a fungal infection to a medical cannabis product has re-ignited discussion about microbial standards, decontamination methods, and the broader question of whether cannabis should be treated first as a plant, or first as a medicine.
The conversation often becomes emotional, particularly around the topic of irradiation. Many patients express a preference for “non-irradiated” products, sometimes due to assumptions about quality or flavour, and sometimes from online advice and peer communities. But as with any prescribed medicinal product, microbial safety standards and regulatory expectations sit above personal preference; particularly in cases where patients may be immunocompromised or otherwise vulnerable.
What is often missing from the debate is context: medicinal cannabis in the UK and Europe is regulated under pharmaceutical frameworks, not consumer or adult-use frameworks. That means microbial load, consistency, documentation, and recall-ability are treated the same way they would be for other herbal medicinal products.
Understanding the Standards
Two microbial standards are often referenced in this space:
- EU Pharmacopeia 5.1.8 (Sub-Section B): Covering herbal medicinal products for oral use.
- EU Pharmacopeia 5.1.4: Sets microbial limits for inhaled pharmaceutical products (e.g., metered-dose inhalers and dry powder inhalers), and its direct applicability to vapourised cannabis flower is not exact.
In simple terms, these standards define how much microbial life may remain on a product, measured in CFUs (Colony Forming Units), before it can be supplied as a medicine. “Microbial life” includes bacteria, moulds, yeasts and fungi which, while naturally present on plants in cultivation environments, are not acceptable on medicinal products destined for inhalation, especially in immunocompromised patients.
Multiple controlled studies and regulatory assessments (not reproduced here, and not being asserted as uniform across all geographies) have shown that achieving these microbial thresholds consistently without any form of decontamination step is extremely difficult, and in many contexts not practically feasible at scale. This is particularly true for products intended for inhalation.
Irradiation vs. Remediation
The public discussion tends to collapse remediation and irradiation into the same category, or contrast them incorrectly. Three important clarifications help:
- Non-irradiated does not mean non-remediated.
A cultivator may still apply remediation steps such as UV, Ozone, steam, hydrogen peroxide, or other interventions. Some of these have quality, safety, or regulatory drawbacks. - Irradiation is regulated and validated.
Electron beam (“e-beam”) and gamma irradiation have decades of data in pharmaceutical and food sterilisation contexts. Dose control is strictly regulated and process validation is standardised.
The question for prescribers is not preference, but risk.
If a doctor supplies a product that has not been sterilised and a patient becomes unwell, the doctor must answer for that decision, including to coroners and regulators where required.
Why Patients Prioritise “Non-Irradiated” (Without Blame)
Patients are not wrong to care about what they put in their bodies. Taste, aroma, and personal autonomy matter. However, the conversation has been shaped heavily by online communities where information and misinformation travel side-by-side, and where cannabis is framed culturally as a botanical product rather than as a medicinal one. That creates tension between preference and pharmaceutical responsibility.
Many of the assumptions patients make; that irradiation “kills the product”, “removes terpenes”, or “ruins the flower”, are either outdated, overstated, or based on high-dose gamma irradiation rather than controlled low-dose e-beam sterilisation. Those distinctions rarely surface in patient dialogue.
Let’s Ask A Medical Practitioner
To explore how this looks from a clinical perspective, and to address some common misconceptions, we spoke with Dr. Rowan Thompson, a prescribing clinician who routinely encounters these questions in practice. Rowan is Vice Chair of the MCCS, with his primary focus being on improving access to education on medical cannabis and the endocannabinoid system for doctors, medical students and allied healthcare professionals.
Q: Rowan, how often do patients ask specifically for “non-irradiated” products?
A: This will normally happen at least once in every clinic. This is sometimes a requirement that patients will disclose when they initially present and are seen by a consultant, and sometimes it’s a request that comes after having trialled irradiated products.
Q: From your perspective as a prescriber, what drives that request?
A: I feel that clinicians are often quite poor at explaining what irradiation is and why it is done for the majority of dried flower products. I think it’s possible to have an image of a non-irradiated flower being more ‘natural’ or ‘pure’ though I wouldn’t agree with this.
A common reason I hear from patients is the feeling that irradiation causes flower to lose its terpenes. This has been explored in the literature and several sources suggest that between 10-20% of total terpene content is lost during irradiation, however other studies demonstrate no loss of terpene content from the irradiation process. I do not personally feel this would compromise a product’s clinical potential though I appreciate this is a subjective take on this. I have also had reports from patients that irradiated flower causes more respiratory side effects like coughing. Some people believe this is due to reduced moisture content in irradiated flower however this isn’t strongly supported in the literature.
I don’t want to devalue patients’ experience and I am definitely not saying patients are wrong if they feel irradiated flower doesn’t suit them. I think it’s important to highlight however that a product being irradiated doesn’t mean the product is faulty or has been inappropriately exposed to harmful bacteria. In fact, many supermarket foodstuffs will go through a process of irradiation to ensure they don’t have microbial contaminants.
Q: One common misconception is that non-irradiated means “non-remediated”. Can you explain why that isn’t necessarily true?
A: Many non-irradiated flowers are instead treated with other sterilisation techniques like ozone treatment. There are benefits and drawbacks to different sterilisation processes and there is no reason to believe that these processes impact the medical properties of flower. Instead, all are shown to reduce total microbial content which makes what is a very safe product even safer! When a product has been irradiated, this information is readily available. This isn’t always the case for other techniques of remediation and it is reassuring to know how a product has been treated.
Q: Another question clinicians face is risk. If a product isn’t sterilised and a patient becomes unwell, what does that mean for the doctor?
A: As a Resident Doctor working under shared care agreement, anything I prescribe is guided by the decision of a patient’s named consultant. This also applies to other non-consultant doctors, nurse prescribers and prescribing pharmacists. I think it’s important to emphasise that any decision about prescribing non-irradiated products is made at the discretion of the named prescribing consultant.
The vast majority of cannabis based medical products that are prescribed in the UK are unlicensed schedule 2 medical products. Schedule 2 drugs are defined as those with potential medical value but are considered ‘highly addictive and subject to misuse’. I don’t imagine that any cannabis prescribing doctor would agree that cannabis fits that criteria, and I certainly don’t personally! The GMC emphasises to doctors that the decision to prescribe an unlicensed medication should be reserved for when no suitable licensed treatments will meet a patients’ needs.
They also state that the risks of prescribing an unlicensed medication must be fully considered and discussed with the patient. Ultimately, the decision on whether to prescribe an unlicensed treatment rests with the consultant doctor. Cannabis is a very safe drug and many clinicians working in this area feel the way it is classified in the UK doesn’t accurately reflect the safety of the medicine. However, whilst it is classified in this way, many clinicians also feel they have a duty to follow this guidance and to prescribe with caution.
For any patient who becomes unwell or even passes away whilst using an unlicensed medication, there is potential for that medication to be heavily scrutinised for the potential role it may have played. The prescribing clinician may be asked to explain and defend their use of an unlicensed medication. By showing that the prescription has been done following a thorough assessment and that a patient has failed on conventional treatment, there is a clear explanation for showing due diligence in choosing to prescribe an unlicensed product. Justifying choosing a product that has not undergone a documented process of irradiation would be difficult and I could not think of a good reason to suggest why a non-irradiated product is ‘more safe’ than an irradiated one. This means many clinicians choose not to prescribe non-irradiated products to patients who are at risk of immunocompromise, and some choose not to prescribe them at all.
There seems to be a lot of misinformation on whether to prescribe irradiated or non-irradiated products. As we’ve established, the purpose of radiation treatment is for sterilisation of microbial contaminants on an organic product. This helps ensure the product meets the EU Pharmacopeia criteria which sets out the upper limit of microbial content a product can contain. A product that meets these criteria can still contain a small amount of microbes.
Some clinicians may want to demonstrate in their prescribing that they have chosen a product that is as safe as possible. Irradiation of cannabis flower can achieve near total sterilisation of the final product, well below what are already very strict standards set out in the EU Pharmacopeia requirements.
Q: Where irradiation is required, would other remediation processes suffice? If not, why not, if they are meeting the required monograph?
A: From a clinician’s perspective, we want to see products that are compliant with regulations and as safe as possible for our patients. A hugely important part of this is transparency and candour. Ensuring all products have full information sheets available for clinicians and patients helps to all parties to be fully informed and make safe and appropriate choices around prescribing. I don’t claim to be an expert on the different forms of remediation however understand that irradiation is the most researched and understood example of current remediation techniques.
Q: How do you explain the pharmaceutical standards piece to patients who view cannabis more like a natural or botanical product?
A: Regardless of whether you agree with the regulations around medical cannabis, I believe these must be followed whilst we continue to advocate for reforms around medical cannabis. We are in a system where the vast majority of prescribed cannabis based medicines are unlicensed products that are subject to higher levels of scrutiny than many other medications.
The MCCS and the APPG on Medical Cannabis included in their 2025 recommendations reclassifying cannabis as a botanical to allow the wider evidence base on cannabis to be considered in the creation of national guidelines. Regardless of how medical cannabis is scheduled, I would expect it to remain subject to appropriate levels of quality regulation to ensure it is as safe as possible.
Q: Finally, do you think this is an education gap, a cultural gap, or a regulatory gap?
A: I feel the UK medical cannabis sector would greatly benefit from more consistent and in depth discussion between clinicians and patients. I feel patients’ concerns are often not properly listened to and understand the frustrations that exist in parts of the patient population. I do also think it is important to remember that both prescriber and patient must be comfortable and happy with a treatment plan and prescribers should not be pressured to prescribe products they are not comfortable prescribing. I would encourage any patient who has questions or concern about irradiated vs non-irradiated products to discuss this with their clinician and to try and appreciate why a clinician may not be comfortable prescribing a non-irradiated product.
This recent case highlights that medicinal cannabis must meet microbial safety standards designed to protect patients, particularly those who are immunocompromised. Inhaled dried flower is exceptionally difficult to supply at scale without some form of remediation, and irradiation remains the most researched and standardised approach in pharmaceutical contexts. Other techniques can also be used, but “non-irradiated” does not mean non-remediated.
Many of the concerns patients raise about irradiation (especially around terpene loss or changes in sensory experience) remain debated, and dosing and methodology appear to be relevant variables. It is also plausible that some of the negative experiences attributed to irradiation are instead the result of upstream factors such as cultivation quality, drying and curing practices, or moisture content rather than the sterilisation process itself.
Preferences should not be dismissed, but prescribers ultimately must prioritise safety and defensibility. If a vulnerable patient becomes unwell, a clinician must be able to justify why a product without a validated sterilisation step was chosen. Clearer communication around microbial standards, remediation methods and the realities of pharmaceutical compliance would help reduce the current disconnect, allowing cannabis to be understood both as a botanical product and as a regulated medicine without compromising safety.
If you are interested in learning more about the MCCS, or becoming a member as a clinician, you can do so here: https://www.ukmccs.org/
Credit: Cannabis Photography by Colin Caswell
