Does GACP Certification Mean PGR-Free? Reading the Thai Standard Line by Line

📊 Testing and Analytics
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A common question among Thai buyers and growers is whether a GACP certificate means the flower was grown without plant growth regulators (PGRs). Some buyers no longer trust the label and judge by feel: buds that seem unusually round, rock hard and heavy. This article looks at what the available translation of the Thai standard actually says. It sets out what the standard covers and what it does not, and explains how to ask a laboratory the right question.

1. Which “PGRs” people mean

As a class, plant growth regulators include auxins and cytokinins used in rooting and tissue culture, as well as gibberellins and abscisic acid. These are routine horticultural tools. “PGR bud” refers to a narrower group of synthetic growth retardants used to make flower compact and dense. The usual three are paclobutrazol, daminozide and chlormequat chloride.

These compounds suppress internode extension and can produce dense, heavy, rounded buds that make average flower look premium. The physical signs do not prove anything, though. Some genetics produce dense, round flower naturally, and late-flower feeding can change bud structure. A suspicious bud is a reason to test. It is not a result.

Regulators elsewhere have acted on two of these compounds. During a US EPA special review in 1989, daminozide’s food-use registrations were cancelled. EPA classifies its breakdown product, UDMH, as a probable human carcinogen (Group B2), and in the US daminozide is now registered only for ornamental and bedding plants. Health Canada requires licensed cannabis producers to test for paclobutrazol (limit of quantification 0.02 ppm) and daminozide (0.1 ppm). Chlormequat chloride is not on Canada’s list, which shows how much panels can differ.

2. Why paclobutrazol is easy to find in Thailand

Paclobutrazol is a mainstream fruit-growing chemical here. Thai growers have used it to induce off-season mango flowering since 1986, usually as a soil drench followed by a thiourea spray, and Thai university research still describes it as widely used for this. Agricultural chemicals in Thailand are regulated as hazardous substances under the Hazardous Substances Act B.E. 2535, and the Department of Agriculture (DOA) handles registration. This article could not confirm individual paclobutrazol registrations in the DOA database. A product’s registration number and the crops it is approved for are shown on its label.

Being sold legally for mango does not make paclobutrazol a permitted input for GACP cannabis. A pesticide registration covers a labelled product on named crops. GACP is a separate standard for a medicinal herb.

3. What the standard says, in translation

The only full English text that is easy to find is a third-party translation of the Thai Ministry of Public Health’s cannabis GACP guidelines, published by Cannavigia in September 2024. The translation does not give the Thai document’s title, version or year. DTAM has revised its GACP requirements since 2022 and issued related instruments, including a B.E. 2568 DTAM notification on GACP-certified cannabis cultivation sources. The wording below therefore comes from a translation of an unidentified earlier version. It has not been checked against the Thai original currently in force.

Section 9 (Cultivation) of the translation says:

  • 9.2: production “should be mainly based on ecological agriculture”.
  • 9.3: use integrated pest management “and do not use chemicals to prevent and eliminate pests”.
  • 9.4: “When using organic substances or beneficial plant growth promoters, they should be used at an appropriate level”.
  • 9.5: “Only organic or biological substances are permitted for use in pest prevention and elimination, in compliance with the law.”
  • 9.6: agricultural hazardous substances prohibited under the Hazardous Substances Act B.E. 2535 may not be used or possessed.

Sections 5 and 6 require soil, substrate and water samples to be analysed for toxic residues and heavy metals before planting. Plant growth regulators are not mentioned by name, either as a class or as individual compounds.

4. What that settles, and what it does not

In the chemical sense, paclobutrazol, daminozide and chlormequat chloride are organic compounds, but that is not the relevant meaning here. They are synthetic agrochemicals, not organic-agriculture or biological (biocontrol) inputs in the sense the standard uses.

Even so, the translated “only organic or biological substances” rule (9.5) applies to pest prevention and elimination, and growth retardants are not pest-control products. Clause 9.6 catches only substances already prohibited under the Hazardous Substances Act, and no source found for this article places paclobutrazol on that list. Clause 9.4 even allows “plant growth promoters” used “at an appropriate level”.

On this reading, synthetic growth retardants conflict with a standard built on ecological agriculture and organic or biological inputs, and an auditor could reasonably challenge them. However, the translated text has no clear clause banning them. This is an interpretation, not a DTAM ruling, and no DTAM statement on growth regulators specifically could be found. If the question matters commercially, ask DTAM or your certifying auditor in writing.

5. Process certification versus product testing

GACP is a process certification. An auditor checks records, procedures and the input register. The only testing the standard names is environmental: soil, substrate and water before planting. Finished flower is not screened for growth regulators. A farm that used a retardant without recording it would not be caught by a document review.

A certificate of analysis is a product test. It reports what was in one batch, and only for the analytes on the panel (see the article on how to read a certificate of analysis, topic 1318). “No pesticides detected” on a panel that leaves out paclobutrazol tells you nothing about paclobutrazol.

So a GACP certificate means a documented input system passed an audit. It does not guarantee that the product is free of growth retardants.

6. What to do, depending on who you are

Patients and licensed buyers: ask for the certificate of analysis, and ask whether its panel includes paclobutrazol, daminozide and chlormequat chloride. The question is what the panel covers, not only what the result says.

Asking a lab for the right panel: before sending a sample, ask for the full analyte list with the limit of quantification for each compound. Check whether the three compounds are in the default pesticide panel or must be added. If the batch is meant for export, compare those limits with the destination market’s requirements.

Growers: keep a complete input register from day one: product, active ingredient, registration number, batch, rate, date, crop stage and applicator. A complete register is the only practical way to show what was not used. A voluntary finished-product screen that includes these compounds supports B2B and export documentation and buyers’ due diligence. Advertising flower online is prohibited in Thailand, and that includes “PGR-free” claims.

Exporters: the destination market’s residue panel decides whether a batch sells, and it may include compounds a domestic panel leaves out. Canada’s list is one example.

Dispensaries: as of October 2026, cannabis flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis) B.E. 2568. It may be dispensed only against a PT 33 prescription from an authorised practitioner, for no more than 30 days per prescription and with no refills. Sold flower must come from a GACP-certified cultivation site. The two B.E. 2569 Ministerial Regulations tightened licensing in 2026 but did not change the PT 33 prescription rules. Legal commentary notes that without GACP-validated evidence, downstream licences such as dispensary licences may be suspended. That means provenance is your risk as well as your supplier’s.

7. What could not be verified

  • Any DTAM statement specifically on plant growth regulators.
  • The current Thai-language GACP text, and whether the translated clauses above still match it.
  • Which Thai laboratories include these compounds in their standard panels.
  • Any data on how common growth regulator use is in Thai cannabis. The evidence so far is buyers’ impressions.

The standard is not meaningless. What is missing is a verification layer that would let a buyer act on it.

Has anyone had flower tested in Thailand, at a Thai laboratory, on a panel that included paclobutrazol, daminozide or chlormequat chloride? Were they in the default panel, or did you have to ask? No lab advertising, please. Just share the panel facts.

Related topics: 1317, 1318 (how to read a certificate of analysis), 1340 (plant growth regulators).

This article is a reading of published guidance and is not legal or regulatory advice. The authoritative source on what is permitted under Thai GACP is the Department of Thai Traditional and Alternative Medicine and your certifying auditor, and the wording quoted here is from a third-party English translation rather than the Thai original. Cannabis inflorescence is a controlled herb in Thailand under the applicable Ministry of Public Health rules; cultivation and sale require licensing.

Sources

Further reading on Asiannabis

What You May Legally Spray Under Thai GACP, and Why There Is No Cannabis-Specific Product List