CBD and THC explained

Medicinal cannabis in New Zealand comes down to two molecules that appear on every label: CBD and THC. They are not interchangeable, and the ratio between them often matters more than the total amount. THC is the molecule that produces the “high”; CBD does not. Both are prescription medicines under the Medicinal Cannabis Scheme, and the legal route runs through a medical practitioner and a pharmacy, not a dispensary.

The single most useful question is not “is it CBD or THC?” but “what is the THC:CBD ratio, and what is the route?” That ratio and the form determine the experience more than any other variable.

What CBD and THC actually are

Cannabis contains more than 100 cannabinoids, but two dominate prescribing decisions: CBD (cannabidiol) and THC (delta-9-tetrahydrocannabinol).

THC is the main psychoactive compound. It binds strongly to CB1 receptors in the brain, which is why it produces the “high” and can relieve pain, stimulate appetite, and reduce nausea. It is measured in milligrams per gram (mg/g) or as a percentage.
CBD is not psychoactive in the way THC is. It interacts with several receptor systems and is used mainly for anxiety, inflammation, and seizure disorders. It is also measured in mg/g or %.

A third compound, CBDA (cannabidiolic acid), is the raw precursor to CBD and appears in unheated extracts. Terpenes (myrcene, limonene, pinene) are aromatic compounds that modify the effect of cannabinoids; they are listed on some product labels but are not regulated as active ingredients.

How they work

THC binds strongly to CB1 receptors in the central nervous system. That binding produces euphoria, sedation, and appetite stimulation. CBD, by contrast, has a low affinity for CB1 and CB2 receptors. It appears to modulate the endocannabinoid system indirectly, and much of its clinical interest comes from anti-inflammatory, anxiolytic and anticonvulsant activity. The NZ Formulary and Healthify (2024) describe CBD as non-intoxicating at typical prescribed doses, while THC is the main psychoactive compound; a product labelled 10:10 contains 100 mg/g THC and 100 mg/g CBD.

The core comparison

Attribute	THC (delta-9-tetrahydrocannabinol)	CBD (cannabidiol)
Main effect	Psychoactive; produces the “high”	Non-psychoactive; no euphoric high
Primary uses	Pain, muscle spasticity, appetite stimulation, nausea	Anxiety, inflammation, seizure disorders, chronic pain
Onset (inhaled)	5-10 minutes	5-10 minutes
Onset (oral oil)	30-90 minutes	30-90 minutes
Duration (inhaled)	2-4 hours	2-4 hours
Duration (oral oil)	6-8 hours	6-8 hours
Common side effects	Drowsiness, dry mouth, increased appetite, dizziness	Generally well tolerated; can cause fatigue, diarrhoea, or changes in appetite at high doses
Psychoactive	Yes	No (at typical doses)
Legal pathway	Requires a doctor’s script under Misuse of Drugs Act	Requires a doctor’s script under Misuse of Drugs Act (CBD is not controlled, but as a medicine it is prescription-only)

What happens when you take them

Onset and duration depend on the form, not the molecule.

Inhaled (flower or vape): onset 5-10 minutes, peak around 30 minutes, duration 2-4 hours. This suits acute episodes such as breakthrough pain, nausea or panic because you can titrate in near real time.
Oral (oils, capsules): onset 30-120 minutes, duration 6-8 hours. This suits baseline symptoms, sleep or all-day pain control.
Sublingual (oils held under the tongue): onset 15-30 minutes, duration 4-6 hours. This is a middle ground, but you must hold the oil for 60-90 seconds before swallowing.

Bioavailability differs by route. Inhaled THC reaches roughly 25-30%, while oral THC reaches roughly 10-20% because of first-pass liver metabolism (NZ Formulary, 2024). CBD behaves differently: oral CBD has low and variable bioavailability (around 6% in some pharmacokinetic studies), but it has a longer half-life than THC, so effects accumulate over days (Healthify, 2023).

Do not drive after taking THC

THC impairs coordination, reaction time and judgement. The NZ Formulary and Medsafe warn against driving or operating heavy machinery while using THC-containing medicines. If you are starting a new THC product or changing your dose, do not drive until you and your prescriber have established how it affects you. CBD at typical prescribed doses is not considered impairing, but fatigue is a possible side effect. Check the product label and speak with your prescriber about driving restrictions.

The Medicinal Cannabis Scheme

The Medicinal Cannabis Scheme is the legal framework that allows a medical practitioner to prescribe a manufactured cannabis medicine. It is administered by the Medicinal Cannabis Agency, which sits within Medsafe, and operates under the Misuse of Drugs Act 1975 (Ministry of Health, 2020). The scheme does not create a general licence to possess or use cannabis. It creates a prescription pathway.

Since 1 April 2020, the scheme has allowed products that meet GMP standards to be prescribed and dispensed through pharmacies. The Misuse of Drugs (Medicinal Cannabis) Regulations 2019 set out how the scheme works. The Medicinal Cannabis Agency (MCA) issues licences for cultivation, manufacture and supply. Medsafe approves finished products and monitors quality. The NZ Formulary lists those that meet the scheme’s standards, and prescribers use it as the official reference. The Ministry of Health publishes the scheme’s operational rules, including the requirement that all products meet Good Manufacturing Practice (GMP) standards and be approved by the Ministry of Health.

A common misunderstanding is that “legal medicinal cannabis” means a patient can legally smoke raw plant material or buy unregulated goods. Under the scheme, the legal item is a manufactured pharmaceutical, and the raw flower, while available, is prescribed and dispensed through a pharmacy, not a dispensary. The Misuse of Drugs Act governs this pathway.

How the law treats THC

THC is the main psychoactive compound in cannabis. Under the Medicinal Cannabis Scheme, THC content is measured in mg/g or percent and determines both therapeutic effect and the level of regulatory control. High-THC products are used for pain, muscle spasticity, nausea and appetite stimulation. THC produces the “high” that many patients find uncomfortable, so the NZ Formulary and clinical guidance recommend starting at a low dose and titrating slowly. Products containing more than 2% THC are controlled drugs under the Misuse of Drugs Act 1975, which is why they require a script and cannot be legally possessed without one. Medsafe approval under the Misuse of Drugs (Medicinal Cannabis) Regulations 2019 is required for each product before it can be prescribed. The NZ Formulary lists THC and CBD monographs with dosing guidance for clinicians. The evidence base for THC’s efficacy is strongest for chronic pain, nausea and vomiting, and appetite stimulation in palliative care; the evidence for other conditions is less certain.

How the law treats CBD

CBD is non-psychoactive, so it does not produce a “high”; it is used for anxiety, inflammation and seizure disorders. In this country, CBD was rescheduled in 2021 so that products containing 98% or more CBD and 2% or less of other cannabinoids are not controlled drugs, but they still require a script under the Medicines Act. The ratio of THC to CBD determines the clinical experience. High-THC products are used for pain, muscle spasticity and appetite stimulation; high-CBD products are used for anxiety, inflammation and epilepsy. A 1:1 ratio is common for balanced relief. The prescriber’s decision is not “THC is good, CBD is better”; it is about matching your symptom profile and risk tolerance.

How to talk to a prescriber

Book a standard consultation with a medical practitioner who is familiar with the Medicinal Cannabis Scheme. Tell them your diagnosis, what you have already tried, and which symptoms remain uncontrolled. Ask these three questions:

“Is a CBD-only, THC-only or balanced product more appropriate for my symptoms?”
“What route (oral oil, inhaled flower or sublingual oil) suits my daily routine and symptom pattern?”
“What is the starting dose, and how do I titrate up safely?”

If the prescriber determines a cannabis medicine is appropriate, they will write a script for a pharmacy-dispensed product that meets GMP standards. Do not accept unregulated goods. Possession without a script remains illegal.

FAQ

Can I legally buy CBD oil over the counter in New Zealand?

No. Even though CBD is not a controlled drug, it remains a prescription medicine under the Medicines Act. You need a script from a medical practitioner and must collect it from a pharmacy.

Does the Medicinal Cannabis Scheme let me smoke raw cannabis?

No. The scheme covers manufactured pharmaceutical products that meet GMP standards. Raw flower can be prescribed, but it is dispensed through a pharmacy and is intended for vaporisation, not smoking. Possessing or using unregulated cannabis remains illegal.

How long does it take for CBD to work?

Oral CBD has a slow onset (30-120 minutes) and low bioavailability, and its effects accumulate over days. Some people notice a change within the first week; for others, it takes two to four weeks of consistent dosing. Your prescriber should give you a titration schedule and a review date.

Legal and safety note

the material below is for information only and does not constitute medical or legal advice. Medicinal cannabis is a prescription medicine in this country. Always consult a qualified medical practitioner before starting, changing or stopping any treatment. Do not drive or operate machinery while using THC-containing medicines unless your prescriber has confirmed it is safe. Possession of cannabis without a valid script is illegal under the Misuse of Drugs Act 1975.