Decoding Cannabis: missing data in research and what it means for you

A study, whether it be a randomised controlled trial (RCT) or a real-world observational study, is essentially an attempt to turn messy human experiences into something measurable and understandable. That sounds simple enough on paper, but in practice, it usually means collecting a huge amount of information across weeks, months, or years, and then trying to make sense of patterns.

In health research, those patterns often rely on patient-reported outcomes. Pain scores. Sleep quality. Anxiety levels. Appetite. Day-to-day function. These are harder to measure consistently than, say, a blood test. They can also change for reasons that have nothing to do with treatment: stress, routines, other medications, flare-ups, work, family life, you name it.

Add in the fact that different people may be prescribed different strengths, formats, and treatment plans, and it becomes easier to see why results can vary from study to study, even when researchers are asking broadly similar questions.

But there’s another issue that sits underneath a lot of confusion, and it often gets missed in the media coverage entirely: missing data.

(Need a quick refresher on medical cannabis terms? Head to our medical cannabis glossary)

What is “missing data”?

In research, missing data is exactly what it sounds like: That is, data that the researchers planned to be collected, but was not. 

There are usually two main reasons for this to happen in medical cannabis research: 

• Study participants simply drop out of the study or stop responding to the researchers.
• Study participants stay involved, but miss check-ups, questions, or any number of other participant-reported metrics. They complete the baseline questionnaire, then forget the one planned at the four-week mark. They log symptoms for a month, then skip the next two follow-ups. They report benefits, but do not bother reporting side effects unless something feels serious.

This doesn't mean that the study was run badly or even poorly planned, just that the final data set is incomplete. This matters for a few main reasons, but mostly because the data is the heart of the research. Small changes can affect the story the study is telling. 

Say a decent percentage of the study’s participants who were struggling with the treatment due to side effects or a lack of efficacy drop out. Their data stops being collected, which can make the final results look more positive than they actually are, simply because the harder, less desirable experiences are no longer being counted in the final data set. Or vice versa.

Is missing data an issue in medical cannabis research?

An issue? 

No, not really. At least, not in the sense that we can’t trust the growing body of data being released. Missing data is somewhat common across almost all health research, especially when studies run over weeks or months and rely on people reporting how they feel.

But it is something researchers, clinicians, and readers need to keep in mind, because it can shape how results look on paper.

A lot of medical cannabis research focuses on patient-reported outcomes, which can be tricky to quantify across a large study group and are subjective. And when studies stretch over months or even years, there are simply more chances for people to miss a form, skip a questionnaire, or stop responding altogether.

And it is always worth pointing out that medical cannabis treatment is rarely a “set it and forget it” process. 

Most patients go through a period of some trial and error before settling on the specific medical cannabis products, like medical cannabis strains and/or THC vapes, especially if they’re working towards better symptom control with clinical guidance. It is a normal, expected part of medical cannabis treatment, but it can make consistent reporting more difficult.

How robust research methods limit the effect of missing data

Let’s make one thing very clear. Missing data does not ruin studies, at least not good studies that plan for these outcomes.

Researchers have been dealing with this problem for a long time, and better studies tend to do two things well: they report clearly what happened, and they test whether the missing information could have changed the conclusions.

First, they show participant flow transparently. They clearly and openly explain how many people started in the study, how many finished it, and the reasons behind why some chose to drop out. 

Secondly, good studies do not try to pretend that the missing data is irrelevant. Most studies have a clearly labelled ‘limitations’ section, where they explain the issues and what steps they took to reduce the impact. 

Green flags in research papers you can spot in 30 seconds

If you’re scanning a study and questioning the veracity of the results, look for these signs:

• A flow diagram or clear reporting of how many people finished
• Dropout numbers and the reasons explained
• The missing data is mentioned openly as a limitation
• Sensitivity analysis included, where researchers check whether the results still hold up when different reasonable assumptions are made about the missing data, rather than relying on just one interpretation.

Releaf’s largest ever UK medical cannabis patient survey

In late 2025, Releaf conducted the largest UK medical cannabis patient survey ever conducted, with 1,669 responses.

Cannabis for pain was the most reported reason for treatment, which lines up with what we see across the wider UK patient community, where chronic pain is one of the most common drivers for patients searching for alternative treatment options. 

While not a full clinical trial spanning months/years, researchers have consitently highlighted the value of surveys like this. When a large group of active patients answer a comprehnsive list of the same questions, it helps build a much clearer picutre of how the treatment option in question is actually being taken, how effective it is, and if any obvious respondent wide issues are surfaced. 

The key stats from this survey included:

• 97% of patients report improved quality of life
• 78% rate their treatment as ‘extremely effective’ or ‘very effective’
• 88% have not experienced any side effects
• 91% were likely to recommend medical cannabis to others who may be eligible
• 72% have been prescribed medical cannabis to treat more than one condition

Taken together, these results give a solid real-world snapshot, but they also make the main point of this article very clear. Data like this is useful because it reflects real patients, yet it’s still shaped by who responds and how consistently they do so. 

With 1,669 Releaf patients responding and answering the full set of survey questions, we were able to build a much clearer picture of how medical cannabis is being administered in practice, while also seeing first-hand why consistency and completeness of data matter when interpreting any set of results.

Rractical documentation matters at a personal level also. If you’re prescribed medical cannabis, having supporting proof to hand (like your Releaf UK medical cannabis card) can make day-to-day life simpler, particularly if questions ever come up around your prescription.

What does this mean if you’re considering medical cannabis treatment in the UK?

Medical evidence rarely comes with a perfect list of comprehensive results, and that is true for long-term medical cannabis studies, too. And then, when you take into account the oversimplified headlines that most people skim past, it is quite easy to see why there has been so much misinformation spread through hit-job style reporting about medical cannabis in the UK in recent years.

In practice, treatment decisions aren’t based on a single study or a punchy news story. They’re made with clinical guidance, drawing on the wider body of research, real-world patient data, with your individual medical history and health needs guiding your prescribing specialist every step of the way.

If you’re considering whether medical cannabis could be suitable for you, a sensible first step is to check your eligibility. Releaf’s medical cannabis eligibility checker is free, takes under 20 seconds, and gives you a clear starting point, and head to our medical cannabis pricing for a clear explanation of what you can expect to pay for treatment. 

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