Decarboxylation

Decarboxylation is a heat-driven reaction that converts acidic cannabinoids, such as THCA and CBDA, into their active forms, THC and CBD.

When cannabis plants produce cannabinoids, they are in acid form, each of them has an extra group of atoms attached, called a carboxyl group. Heat, time and light can all cause this group of atoms to break off and escape as the gas carbon dioxide.

At a glance: Cannabis decarboxylation

What is decarboxylation?

Cannabis decarboxylation is when a heat is used to convert acidic cannabinoids into their active forms.

Heating cannabinoids to a specific temperature for a set amount of time causes the THCA and CBDA to decarboxylate and turn into THC and CBD.

Cannabinoids are not psychoactive in their acid form, but still have potential medical value. Vaping or ingesting decarboxylated medical cannabis can lead to intoxicating effects, depending on the dosage size. 

What temperature does cannabis decarboxylate at?

There is no single best temperature for decarboxylation as each choice comes with its own trade-off between speed, vapour production and loss. 

In lab tests at 110°C, THCA had almost fully converted within 30 minutes, and CBDA converted at roughly half the speed. Medical vaporisers typically heat cannabis flowers to 160-220°C which is high enough to convert acid cannabinoids into their active forms and turns them into vapour in a matter of seconds. THC and CBD are believed to have boiling points of 157°C and 160–180°C, which is why vaporisers are set above these temperatures.

This temperature range changes what you inhale as lower settings produce less vapour but preserve more of the terpenes. Higher settings release more cannabinoids but the vapour can feel harsher. Anything above about 230°C begins to make the plant material burn.

Time and temperature work together to decarboxylate medical cannabis, the hotter the temperature, the faster the reaction. However, excessive heat doesn’t just burn and waste cannabinoids, it changes them.

Too much heat can break THC down into CBN, a weaker cannabinoid which produces different effects. Vaporising limits this by releasing cannabinoids quickly, but setting the temperature too high increases the risk of degradation.

Setting the temperature too high can also degrade terpenes, the aromatic compounds found in cannabis flowers. Terpenes are thought to enhance the effects of cannabinoids when consumed together and is a theory known as the “entourage effect.”

Terpenes are more volatile than cannabinoids like THC and CBD and the higher the temperature the more terpenes are lost before being inhaled. 

How long does it take to decarboxylate THC?

Decarboxylating THCA to convert it into THC can take anywhere from 30 minutes to hours when using heat as a method. Vaporising medical cannabis flower, which is in its acid form, takes seconds to heat up as the temperature is likely much higher.

The lower the heat, the longer it takes to decarboxylate THC, the higher the heat, the less time it takes.

Why raw cannabis is not intoxicating

Raw cannabis contains very little THC, but it does contain THCA, the acid form. The two molecules are almost identical but THCA carries an extra carboxyl group which changes how it behaves in the body.

THC produces its intoxicating effects by attaching to CB1 receptors in the brain, which are part of the endocannabinoid system in the body. However, THCA’s extra group of atoms cause it to be bulkier and change its shape, so it cannot attach to the receptors as strongly. 

Turning THCA into THC makes the molecule fit the receptor and attach better. The same applies for CBDA and CBD although neither are intoxicating.

Because prescribed cannabis flower is in its acid form, labels may list THCA and THC separately or a total THC figure. Total THC estimates how much THC would be available if all of the THCA was converted.

Your clinician will take the product's cannabinoid content into consideration when deciding your dose.

Conversion can vary on the device and temperature so you should always follow your prescription as written and speak to your clinician before changing your device.

How does cannabis decarboxylation happen?

Decarboxylated cannabis needs energy to break the carboxyl group away from the cannabinoid and heat is the most effective way to supply it, although time, light  and oxygen also play a part.

Heat is the main driver for cannabis decarboxylation and the higher the temperature, the quicker it happens. 

THCA can convert to THC naturally if left in the right conditions, but it is very slow. As cannabis dries and cures, a small amount of THCA gradually converts to THC over months and years. This is why stored cannabis can contain some THC and CBD even though the plant mainly produces acid forms, natural ageing doesn’t achieve full conversion and causes cannabinoids to break down.

Light, especially sunlight and UV, speeds up both decarboxylation and degradation, causing cannabinoids to break down and reduce their potency.

Oxygen doesn’t drive decarboxylation directly but once THC has formed, exposure to air gradually turns it into CBN which is a weaker cannabinoid.

Why it matters for medical cannabis patients

As prescribed, medical cannabis flower is supplied in its acid form, and needs heat to become active. Patients will need to know how decarboxylation helps keep a consistent dose.

A medical cannabis vaporiser turns THCA and/or CBDA into THC and/or CBD at the point of inhalation under controlled temperatures.

Patients may set their vaporiser between 160-220°C which allows decarboxylation to happen and turns the cannabinoids into vapour, without burning the plant material.

Other products like oils and edibles have gone through decarboxylation during the manufacturing process so the cannabinoids are in their active form already and don’t need further heating.

Your clinician would have taken the form of the medication you are prescribed into account when setting your dose and it’s important to follow your prescription as written.

Medical Cannabis in UK law

In the UK, cannabis-based products for medical use (CBPM) have been legal since November 2018 but only when prescribed by a specialist doctor. 

Prescribed cannabis flower is intended to be vaporised using a medical vaporiser and your prescription will set out how it should be used.

Smoking cannabis is illegal in the UK, even with a medical cannabis prescription. Patients must also not cook with, extract from or modify their prescribed medical cannabis flowers as it could invalidate your prescription.

Home preparation makes it impossible to know how much THC or CBD you're taking, and belongs to the illicit market.

Frequently asked questions about cannabis decarboxylation 

What happens when you decarb cannabis?

Decarboxylating cannabis uses heat to remove the carboxyl group of atoms from acidic cannabinoids, releasing it as carbon dioxide. This turns THCA and CBDA into the active forms of THC and CBD.

Is decarboxylation necessary for edibles?

Yes, as raw cannabis that has not gone through decarboxylation is not active and intoxicating. Medical edibles and oils go through the process during manufacturing. UK patients must not make edibles from prescribed cannabis flower.

Does decarboxylation happen naturally?

Yes, THCA can convert to THC naturally, but it is a slow process, over months and years. Heat and light can gradually convert a small proportion, while oxygen slowly turns THC into CBN.

What temperature destroys cannabinoids?

Above around 230°C plant material starts to burn destroying cannabinoids through combustion, vaporisers avoid this by heating the flower briefly at a controlled temperature. 

What happens if you over-decarboxylate cannabis?

Too much heat degrades cannabinoids rather than activating them. THC can turn into CBN, a weaker cannabinoid, and causes terpenes to evaporate.

Does vaping decarboxylate cannabis?

Yes a medical vaporiser converts THCA and/or CBDA into THC and/or CBD within seconds.

How long does decarboxylation take?

The length of time decarboxylation takes depends on the temperature, at vaporising temperatures it takes a matter of seconds.

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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