What does “Randomised controlled trial” mean?

A study in which participants are randomly assigned to receive a treatment or a comparator, allowing cause and effect to be assessed.

Randomised controlled trial in plain English

A study in which participants are randomly assigned to receive a treatment or a comparator, allowing cause and effect to be assessed.

Randomisation is what distinguishes a trial from an observation: it balances known and unknown differences between groups, so a difference in outcome can be attributed to the treatment.

In this field the controlled trials that exist are mostly small and short. That is the central limitation of the evidence base, and it is why honest guidance hedges.

Frequently asked questions

What does randomised controlled trial mean?

A study in which participants are randomly assigned to receive a treatment or a comparator, allowing cause and effect to be assessed.

Sources and further reading

Every factual statement on this page is drawn from the following public sources. Links open in a new tab and are not affiliated with Flora House.

  1. NICE guideline NG144: Cannabis-based medicinal products
  2. NHS: Medical cannabis (and cannabis oils)
  3. MHRA: The supply, manufacture, importation and distribution of unlicensed cannabis-based products for medicinal use

Patient guide · Written by the Flora House editorial team · Last reviewed: 8 September 2026