Strains

The term ‘strain’ is widely used to describe cannabis plant varieties, but the correct scientific term is cultivar (short for cultivated variety).

Cultivars are plant varieties that have been selectively bred by humans to enhance certain characteristics, such as cannabinoid content, terpene profile, and growing traits.

At a glance: Cannabis strains

Cannabis Strain vs Cultivar

While ‘cultivar’ is the correct scientific term used to describe different cannabis plants, it’s likely that ‘strain’ will still be used, especially in recreational cannabis circles.

‘Strain’ has been used in agricultural society to identify different varieties of crops based on their physical appearance and growth patterns. When cannabis began to be widely cultivated and sold, ‘strain’ was already ingrained in society’s vocabulary, making it a familiar way to describe different types of cannabis.

However, ‘strain’ has no fixed scientific definitions and black market cannabis with strain names attached can massively differ as they are homegrown and not lab tested.

‘Cultivar’ is a formally recognised botanical term governed by the International Code of Nomenclature for Cultivated Plants, which regulates names for plants originating from selective breeding by humans that can be reproduced with consistent traits.

Medical cannabis products in the UK are produced under pharmaceutical manufacturing standards and are labelled with the cannabinoid content, using precise terminology like cultivar supports clinicians to prescribe patients accurately and with consistency.

But even the term ‘cultivar’ has its limitations. While it can tell you a plant variety’s name and breeding lineage, it doesn’t say what effects it produces. Now, researchers prefer to describe what’s actually inside the cannabis plant using one of two key terms: chemovars and chemotypes.

'Chemovar’ is short for ‘chemical variety’ and focuses on the chemicals a plant produces such as cannabinoids and terpenes.

The dominate cannabinoid produced by a plant are classified by chemotypes and there are three main categories:

• Chemotype I: THC-dominant plants with relatively low CBD levels

• Chemotype II: Balanced plants that produce both THC and CBD in similar proportions

• Chemotype III: CBD-dominant plants with very little THC

How are different strains of cannabis categorised?

Cannabis ‘strains’ are typically sorted into four groups:

• Indica plants tend to be short and bushy with wider leaves, they flower quickly and are associated with relaxing effects.

• Sativa plants are taller with narrow leaves, it takes longer for them to flower and are associated with uplifting effects.

• Ruderalis: Short, hardy plant that is able to flower automatically, rarely used as a standalone plant for medical cannabis.

• Hybrid plants are varieties that have been cross-bred between different cultivars to combine traits.

The labels above describe how a plant looks and grows, not the effects they have, which is where chemovar comes in. Medical cannabis clinics focus on the levels of THC and CBD over indica or sativa labels. 

What makes cannabis strains different?

The effects of cannabis may differ even if two cannabis flowers have the same label as every cannabis cultivar has its own chemistry makeup.

There are three main components to this: the cannabinoid content, terpene profile, and conditions in which the plant was grown.

THC and CBD are the two best-known cannabinoids. THC is the main intoxicating compound in cannabis, while CBD is non-intoxicating and has potential therapeutic effects.

Terpenes, which are the aromatic compounds that give different cannabis cultivars their distinct smell and flavours, are thought to enhance the effect of cannabinoids, research is limited but it is a theory known as the “entourage effect.”

The chemistry of the cultivar is also affected by how it is grown and harvested. Light, temperature and storage all affect the levels of cannabinoids and terpenes that remain intact in the cannabis flower.

The way in which medical cannabis is consumed can also play a role, for instance, vaporising cannabis flower can take effect within minutes, but oils and edibles have a delayed onset of effects but last longer.

Each patient is also different, their weight, metabolism, tolerance and other medications can all change how a cultivar interacts with them.

When people describe a strain as “strong”, they usually mean it has a higher THC percentage.

A higher THC percentage is not a better treatment for everyone, some may experience side effects such as anxiety, paranoia, dizziness, and dependency which is why a specialist doctor determines the right dose and frequency for each patient.

Cannabis strain names explained

Cannabis strain names such as Blue Dream, White Widow or Lemon Haze work more like branding than scientific labels. No official system governs them, and these names can follow a few patterns.

Blue Dream is reported to be a cross between Blueberry and Haze, named after its parentage; White Widow is named for its frosty-looking coating of resin; and Lemon Haze is named after its citrus aroma.

On the black market, anyone can use a strain name, and there is no way to check if it’s accurate. Two products with the same name may have different genetics and chemistry. A name can hint at the plant’s history or aroma, but only lab tests can confirm its THC, CBD, and terpene content.

Medical cannabis clinics may also use these names to help identify products, but they use documented levels of cannabinoids and terpenes to guide prescribing and suitability for each patient.

What cannabis strains are legal in the UK?

Medical cannabis has been legal to prescribe by a specialist doctor in the UK since November 2018; recreational cannabis remains illegal as a Class B drug under the Misuse of Drugs Act 1971.

Prescribed cultivars are held to pharmaceutical standards, lab-tested for cannabinoid and terpene content as well as contaminants, and labelled with their THC and CBD percentages.

Find out more about the cultivars available to UK patients.

How does a clinician match cannabis cultivars to a patient?

No individual cultivar is ‘best’ for any condition, instead, specialists choose a product based on the individual patient.

The clinician will review a patient’s medical history, symptoms, previous treatments, current medications and history of mental illness. Patients also need evidence that two or more traditional treatments have not provided relief before medical cannabis can be considered.

From there, your clinician will consider the cannabinoid profile, the strength, the terpene profile and the product form.

Frequently asked questions about cannabis strains

What do cannabis strains mean?

A cannabis strain is often used to describe the variety of a cannabis plant that has been selectively bred by humans in recreational circles. In medical and scientific industries the variety of plants are called cultivars.

What is the difference between a strain and a cultivar?

Both strain and cultivar describe cannabis varieties, but cultivar is the formally recognised term in science and medical fields.

What cannabis strains are available in the UK?

Medical cannabis is available in the UK when prescribed by a specialist doctor. Find out more about the cultivars available to UK patients.

Are indica and sativa still relevant?

Indica and sativa describe how a plant looks and grows, but they are not reliable guides regarding its effects.

What makes one strain stronger than another?

Strength usually refers to THC percentage, which measures concentration rather than dose. A higher THC level does not necessarily mean better treatment and can cause side effects such as anxiety, paranoia, and dizziness.

Should a beginner choose indica or sativa?

Cultivar choice is a clinical decision made by a specialist doctor who can prescribe medical cannabis as indica and sativa labels do not reliably predict effects..

Why do strains have such strange names? 

Strain names come from parentage, physical appearance and smell. They are more of a branding tactic rather than a scientific description.

To find out if you are eligible, try our free medical cannabis eligibility checker, it takes less than 30 seconds to fill in.

Our medical cannabis glossary can also help you learn more about terms you may associate with medical cannabis. 

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