CBD vs THC: Chemistry and Labels

Last updated October 2026.

CBD (cannabidiol) and THC (delta-9-tetrahydrocannabinol) are the two cannabinoids people ask about most. They come from the same plant and share the same chemical formula, yet the law handles them very differently and they appear on lab reports in their own distinct ways. This article covers the chemistry, the legal status in Thailand and how to find each one on a product label or certificate of analysis; it does not cover health uses.

At a glance

CBD and THC share the formula C21H30O2 but have different structures.
Fresh flower contains mostly the acid forms, THCA and CBDA, which convert over time or with heat.
Labs report Total THC = delta-9-THC + (THCA × 0.877), so compare Total THC with Total THC.
Since June 2025, cannabis flower in Thailand is supplied only against a valid prescription.
Extracts with more than 0.2% THC by weight remain narcotics.

Same formula, different shape

CBD and THC both have the chemical formula C21H30O2. Molecules that share a formula but have a different structure are called isomers, and that difference in shape is what makes them behave differently.

The cannabis plant makes both through the same pathway. It starts with a compound called cannabigerolic acid (CBGA). At the final step, one enzyme (THCA synthase) turns it into THCA, while another (CBDA synthase) turns it into CBDA. Which of these dominates depends on the plant, which is why some plants are THC-rich and others CBD-rich.

THC acts as a partial agonist at the body’s CB1 and CB2 cannabinoid receptors and is responsible for the intoxicating effect of cannabis. CBD does not have the same psychoactivity and is not intoxicating in the way THC is.

The acid forms: THCA and CBDA

Fresh cannabis flower contains mostly the acid forms, THCA and CBDA, rather than THC and CBD themselves. Over time, or when heated, these acids lose part of their structure (a process called decarboxylation) and become THC and CBD.

Three stages showing how the cannabis plant makes THC and CBD: CBGA, then the acid forms THCA or CBDA, then THC or CBD after heating or ageing. — Sources: Wikipedia (Cannabidiol; Tetrahydrocannabinol).

This happens slowly in storage too. In a one-year storage study, THCA in THC-rich flower kept at 25 °C fell by about a third as it converted to THC. That is one reason two tests of the same batch, months apart, can show different numbers.

How CBD and THC appear on a CoA

A certificate of analysis (CoA) is the lab report for a batch. On a cannabinoid panel you will usually see separate rows for THCA, delta-9-THC, CBDA and CBD, often with minor cannabinoids such as CBG and CBN as well.

Total THC

Because flower contains so much THCA, labs usually report a Total THC figure. The common calculation is:

Total THC = delta-9-THC + (THCA × 0.877)

The 0.877 factor accounts for the weight lost when THCA converts to THC. So a flower showing a low delta-9-THC figure can still have a high Total THC once the THCA is counted. When comparing products, compare Total THC with Total THC.

Other things to check

Beyond the totals, a few details show whether the report fits the product. Our guide to what GACP and CoA mean goes through a full report.

Units: flower results are usually a percentage by weight. Oils and edibles may be shown per millilitre, per gram or per piece.
ND and LOQ: ND means not detected, and LOQ is the lowest level the lab can reliably measure.
Measurement uncertainty: where shown, this is the lab’s margin of error.
Batch ID and test date: make sure they match the product you are looking at.

How to read the cannabinoid panel of a certificate of analysis: the Total THC formula, plus units, ND and LOQ, and batch ID and test date. — Source: Missouri Department of Agriculture, Certificate of Analysis Guide.

Legal status in Thailand

THC-rich cannabis flower

Cannabis flower is a controlled herb under the Thai Traditional Medicine Act. Since June 2025, licensed outlets may only supply it to a buyer who presents a valid prescription, normally on the official form known as ภ.ท.33 (PT 33). Seven professions may issue one: medical doctors, Thai traditional medicine practitioners, applied Thai traditional medicine practitioners, traditional Chinese medicine practitioners, pharmacists, dentists and folk healers.

Sales are not allowed to anyone under 20 or to pregnant or breastfeeding women, smoking is not permitted on dispensary premises, and recreational sales and online sales are not allowed. Our page on cannabis rules in Thailand for visitors has more detail.

Extracts and CBD products

When cannabis came off the narcotics list in 2022, extracts were handled separately: an extract with more than 0.2% THC by weight remains a narcotic. As of October 2026, that is still the position, and a draft Cannabis Control Act is under review but is not yet law. CBD products under the THC threshold are generally sold without a prescription, but they must still meet the rules for their product type, such as Thai FDA registration for packaged foods.

Reading a product label

A label should let you match a product to its lab report. Research on CBD products sold online in the US found that most were not accurately labelled for CBD, and some contained THC, so a few checks are worthwhile.

Both amounts: look for both CBD and THC amounts, not just one.
The unit: check whether figures are per pack, per piece, per millilitre or a percentage.
The batch number: match it with a CoA from an independent lab.
Missing data: be cautious of labels with no batch number or no test data.

This article does not cover health uses of CBD or THC. For any health question, please speak to a Thai-licensed medical practitioner.

Key takeaways

If you would like to talk any of this through, you are welcome to visit our store on Pattaya 3rd Road or contact the CannaBuri team with your questions. We can walk you through the cannabinoid section of any CoA we hold.

This article is general information, not legal or medical advice.

CBD vs THC: Chemistry, Legal Status and Lab Labels

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