Medicinal-cannabis clinical trials

Clinical trials are the engine that separates a regulated medicine from a herbal remedy. For medicinal cannabis in New Zealand, the rules are strict: a preparation cannot be prescribed, dispensed, or imported unless it has been through the same testing framework as any other pharmaceutical. the material below explains how those trials work, how to read the evidence, and how to check whether something you are considering has actually been through the process. It is written for patients, whānau, clinicians, pharmacists, and anyone who needs to tell a verified claim from a marketing claim.

What a medicinal-cannabis clinical trial actually is

A clinical trial is a structured experiment in humans, designed to answer a specific question about a medicine or intervention. In the context of medicinal cannabis, the question is usually whether a preparation containing CBD, THC, or both is safe and effective for a defined condition (for example, chronic pain or epilepsy). The trial compares the preparation against a control, which can be a placebo, an existing treatment, or a different dose of the same preparation. The outcome is measured objectively, and the results are analysed statistically to decide whether any difference is real or due to chance.

A trial is research, not treatment. It answers a question under controlled conditions; it does not guarantee a patient access to a preparation. The results of trials feed into the evidence base that clinicians use, but they do not guarantee that something will work for any given person.

The legal boundary in New Zealand

Under the Medicinal Cannabis Scheme (effective 1 April 2020, per the Misuse of Drugs (Medicinal Cannabis) Amendment Act 2018), a preparation can be prescribed only if it is a “controlled drug” manufactured to Good Manufacturing Practice (GMP) standards and notified to the Ministry of Health. The raw plant material, if prescribed, is dispensed through a pharmacy as a manufactured pharmaceutical, not through a dispensary and not for smoking. This is the single most important boundary: a prescription does not legalise possession of unregulated plant material.

A medicinal-cannabis preparation used in a trial is treated as an unapproved medicine unless it has been approved by Medsafe under the scheme. The Ministry of Health’s Medicinal Cannabis Agency (MCA), part of Medsafe, runs the scheme and sets the quality and licensing rules. A clinical trial in New Zealand is a formal research study in human participants, conducted under the rules of the Ministry of Health and the Health and Disability Ethics Committees (HDEC). The trial must use a preparation that meets GMP standards and is approved under the Misuse of Drugs Act 1975.

The four phases of medicinal-cannabis trials

Clinical trials run in four phases, each with a different question. Understanding the phase tells you how much evidence exists and what kind of claim a company can legally make.

Phase 1: Safety and dosing

• Participants: small group (usually 20-80 healthy volunteers or patients).
• Goal: find a safe dose range and identify side effects.
• Relevance to cannabis: establishes maximum tolerated dose of THC or CBD in humans; often done with single-dose or short-course exposure.
• What you can conclude: “The preparation is safe enough to test in patients,” not “it works.”

Phase 2: Early efficacy

• Participants: 100-300 patients with the target condition.
• Goal: test whether the preparation has a measurable effect and refine dosing; may be open-label or randomised.
• Relevance: many CBD/THC preparations stop here; positive phase 2 results are not proof of efficacy.

Phase 3: Confirmatory trials

• Participants: hundreds to thousands of patients, often multi-centre.
• Goal: confirm efficacy, monitor adverse effects, compare with standard treatment or placebo.
• Relevance: this is the phase that produces the evidence used in prescribing decisions and registration.

Phase 4: Post-marketing surveillance

• Participants: real-world patients after approval.
• Goal: monitor long-term safety and rare adverse effects.
• Relevance: in New Zealand, this is ongoing once a preparation is approved and prescribed.

How controls, blinding and comparators make results trustworthy

A “control” is a comparison group that does not receive the active treatment. In medicinal-cannabis trials, the control is usually a placebo that looks and tastes identical (e.g., placebo oil or placebo flower) so patients and assessors cannot tell the difference. Blinding means neither the patient nor the researcher knows who gets active treatment until the trial ends. In some trials, an active comparator (another medicine) is used instead of placebo; this tests whether cannabis is at least as good as the standard treatment, not just better than nothing.

How to read a trial report

When you are reading a medicinal-cannabis trial, ask four questions before you accept its conclusion:

1. Was it randomised and controlled? A randomised controlled trial (RCT) compares the preparation against a placebo or an active comparator. Uncontrolled observational studies cannot prove cause and effect.
2. Was the preparation standardised? The label must state the exact THC and CBD content in mg/g or %. If the preparation is not standardised, the results cannot be replicated.
3. Who funded it? Industry-funded trials are common in this field; check the conflicts of interest and whether the authors had access to raw data.
4. What was the outcome measured? Patient-reported pain scores, quality-of-life scales, and seizure diaries are valid, but they are not the same as objective biomarkers. Be clear about what was measured.

How to check registration and publication

Registration

In New Zealand, the primary registry is the Australian New Zealand Clinical Trials Registry (ANZCTR), and most trials also register internationally with ClinicalTrials.gov. Registration before enrolment is mandatory for publication in reputable journals. Check the registry entry for the trial ID, sponsor, primary outcome, and whether the trial is recruiting.

Publication

A trial is only as good as its publication record. Use PubMed, Google Scholar, and the Cochrane Library to find systematic reviews and peer-reviewed trials. Beware of “research” published in predatory journals or by companies marketing a preparation.

A five-step method for evaluating a medicinal cannabis preparation

Use the same framework a pharmacist would use. If a preparation fails any of these five checks, it is not a legally dispensable medicinal cannabis item in New Zealand.

1. Check the legal status: is the preparation listed on the NZ Formulary and does it have a Medsafe approval or a Section 29 exemption?
2. Check the cannabinoid content: confirm the THC and CBD content in mg/g and the THC:CBD ratio; this determines the expected effect and side-effect profile.
3. Check the GMP certification: GMP status is mandatory for legal supply.
4. Check the onset and duration: these differ by form (flower vs oil) and affect dosing.
5. Check the stability and batch testing certificate: verify that the preparation has been tested for consistency and contaminants.