When Drug Science launched Project Twenty21 in early 2020, the ambition was transformative: enrol 20,000 patients, collect real-world evidence on medical cannabis at scale, and create the dataset that would convince NICE and the NHS to fund prescriptions. The target enrolment date was the end of 2021.
Five years later, where does the project stand?
What the Project Achieved
Project Twenty21 has enrolled more than 10,000 patients across the UK, making it the largest observational study of prescribed cannabis in British history. The data generated has been substantial. Published analyses have covered chronic pain, anxiety, PTSD, and multiple sclerosis, with most showing positive patient-reported outcomes across multiple domains.
The project succeeded in making medical cannabis more accessible. Participating clinics offered reduced consultation rates for Twenty21 patients, bringing the initial cost of access below what many private clinics were charging. For thousands of patients who could not have afforded treatment otherwise, the project was the difference between access and exclusion.
Politically, Project Twenty21 shifted the conversation. By presenting data in peer-reviewed publications and parliamentary submissions, Drug Science created a body of evidence that policymakers and clinicians could engage with seriously — something that did not exist in the UK before 2020.
Where It Fell Short
The 20,000-patient target was not met. By the end of 2021, enrolment was well below projections, and the timeline was quietly extended. The reasons were multiple: recruitment proved slower than anticipated, funding was constrained, and the COVID-19 pandemic disrupted clinical operations for much of 2020 and 2021.
The evidence generated, while substantial, has not shifted NICE's position. NICE continues to cite a lack of randomised controlled trial data as the barrier to recommending NHS prescribing. Observational studies — even large ones — do not meet the evidentiary threshold the institute requires. This has been the project's central frustration: it built exactly the dataset it set out to build, and the target audience declined to be persuaded by it.
There is also the question of patient outcomes beyond survey data. Project Twenty21 relies on patient-reported outcome measures — standardised questionnaires that capture subjective experience. These are valid and useful, but they are not the same as clinical outcomes verified by independent assessment. Critics within the medical community have pointed to this limitation as a reason the data has not had greater policy impact.
What Comes Next
Drug Science has announced that Project Twenty21 will continue, with an expanded focus on specific conditions and a greater emphasis on data that can support regulatory applications. The project's leadership has acknowledged the need for more structured evidence and has begun exploring partnerships with NHS trusts for controlled evaluations.
The legacy of Twenty21, whatever its limitations, is that it proved something important: large-scale patient registries are possible in UK cannabis medicine. The patients are there, the clinicians are there, and the willingness to participate in research is there. Whether the evidence changes policy is a question for the policymakers. The data, at least, is now in their hands.
