Testing Cannabis Flower Before Export: Moisture, Thai Laboratories and the Final Certificate Check (Part 2 of 2)

💊 Medical Cannabis 💡GACP – GMP – EU-GMP – Export
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Before cannabis flower is exported from Thailand to a medical market, each batch needs a certificate of analysis (COA), the laboratory report that lists what the batch contains. Thai GACP certification (Good Agricultural and Collection Practices, the cultivation quality standard) and the export permit set only a minimum. European and Australian buyers measure against much stricter limits. Part 1 covered the European standard, the method behind the THC figure, microbe limits and decontamination. This part covers moisture, how to choose a Thai laboratory, what destination regulators add, and a final check before you send a COA.

This is Part 2. Part 1: Testing Cannabis Flower Before Export: What a Lab Certificate Must Show for Overseas Buyers (Part 1 of 2)

5. Moisture: two measurements that answer different questions

ASTM D8197 sets a water activity range of 0.55 to 0.65 aw for dried cannabis flower. ASTM International is a standards organisation based in the United States. Water activity (aw) measures how much of the water in the flower is free for microbes to use. It runs from 0 (completely dry) to 1.0 (pure water).

Industry technical literature reports three thresholds:

  • above 0.65 aw, mould growth becomes possible
  • from 0.70 to 0.75 aw, most Aspergillus moulds can start to grow
  • at 0.80 aw and above, most mould failures occur

Storage at 55–62% relative humidity (RH) matches the ASTM window. Flower kept at 58% RH settles at about 0.58 aw.

The pharmacopoeia uses a different control: loss on drying, maximum 12.0%. Loss on drying measures the total water in the flower. Water activity measures only the water that microbes can use, so it predicts whether the flower will stay free of microbes. Loss on drying does not predict that.

A batch can pass loss on drying and still fall outside the ASTM water-activity window. The reverse can also happen. Specify both in a supply contract. A contract that names only one leaves a gap that either side can dispute later.

Translator’s note: in Thailand, outdoor humidity is often far above 62% RH, especially in the rainy season. Well-dried flower can take up water again during storage or transport if the containers are not sealed. A power cut that stops dehumidifiers and air conditioning can have the same effect. Measure water activity on every batch just before packing, with your own meter or through a laboratory, and record it with the batch number. The reading shows whether the batch is inside the window before it ships, and it gives you a record if the buyer disputes moisture later. For drying in Thai conditions, see Drying Cannabis at 85–95% Ambient Humidity. For storage, see Storage: Humidity, Light, Oxygen, and Shelf Life.

What to do: write both limits into the contract: loss on drying no more than 12.0%, and water activity within 0.55–0.65 aw.

6. Laboratories in Thailand: what is still uncertain

Laboratories show their competence through ISO/IEC 17025 accreditation. This is the international standard for testing laboratories. Accreditation means an independent body has checked that the lab can carry out specific tests correctly. Thailand has more than one accreditation route, including:

  • the Bureau of Laboratory Quality Standards (BLQS) of the Department of Medical Sciences (DMSc), Ministry of Public Health, which publishes a searchable register. It is listed as a signatory of the ILAC MRA for testing laboratories (ISO/IEC 17025). The ILAC MRA is an international agreement under which member accreditation bodies recognise each other’s accreditations
  • the Thai Industrial Standards Institute (TISI) accreditation office. Check its current ILAC MRA status on the ILAC signatory list.

Look up any laboratory in the relevant register. Then ask for its scope certificate, the list of the exact tests and methods it is accredited for. ISO/IEC 17025 accreditation covers defined test methods, not the laboratory as a whole. A lab can be accredited for heavy metals but not for microbiology.

Several organisations are relevant. Confirm the cannabis scope of each directly:

  • Central Laboratory (Thailand) Co., Ltd., which is state-owned and publishes its own accreditation list
  • the Government Pharmaceutical Organisation (GPO), which produces cannabis oil for medical use
  • various private laboratories that advertise THC and CBD testing

There is no public combined list of Thai laboratories accredited for the full flower panel. The full panel means cannabinoids by HPLC (high-performance liquid chromatography), pesticides, heavy metals, microbiology and aflatoxins. Anyone choosing a lab should get the scope certificate. They should also find out, separately, whether the destination regulator recognises Thai accreditation at all. These are two different questions, and the second one often causes the problems.

There is also no confirmed ISO product or method standard specific to cannabis. ISO/IEC 17025 covers laboratory competence, and ASTM D8197 covers water activity. If someone refers to “the ISO cannabis standard”, ask them for its number.

Translator’s note: a practical order of steps for a Thai exporter:

  1. Ask the buyer in writing which laboratories or accreditations they accept. This shows whether a Thai COA will count at all.
  2. Ask the Thai laboratory for its scope certificate, and tick off each test in the buyer’s panel against it. This shows which tests are accredited and which are not.
  3. Send a small trial batch and split the sample. One half goes to the Thai lab and one half to the buyer’s lab. Comparing the two results shows whether they agree before a full shipment depends on them.

What to do: do not accept a COA for export use until you hold the lab’s scope certificate and it covers every test the buyer requires.

7. What destination regulators add on top of the Thai minimum

Taken together, the requirements in both parts include several items that often surprise a first-time exporter:

  • Pesticide testing to Ph. Eur. chapter 2.8.13 (Ph. Eur. is the European Pharmacopoeia, Europe’s official book of medicine standards). This chapter has its own table of limits for herbal drugs, and its own rules for pesticides that are not listed. A revision was proposed in Pharmeuropa issue 38.3 (2026). Pharmeuropa is the journal where drafts are published for comment.
  • EU food MRLs (maximum residue limits) under Regulation (EC) No 396/2005, which buyers may also apply through the contract. This includes that regulation’s default of 0.01 mg/kg for pesticides without a specific limit. The default comes from EU food law, not from the Ph. Eur. rule.
  • Heavy metals at the patient-prescribed limits: arsenic ≤0.2, cadmium ≤0.3, lead ≤0.5 ppm, rather than the general herbal limits.
  • Aflatoxin B1 (a mould toxin) at 2 µg/kg, often with total aflatoxins as well.
  • Microbiology for the inhaled route, which for yeast and mould is ≤20 CFU/g (colony-forming units per gram).
  • Total CBN (cannabinol plus its acid form) as a marker of age and degradation.
  • Physical specification: foreign matter, seeds and leaf size.
  • An irradiation declaration, plus authorisation from BfArM (Germany’s Federal Institute for Drugs and Medical Devices) when Germany is the destination.
  • GACP evidence with batch traceability attached to the certificate itself.

Residual solvent testing usually does not apply to unextracted flower, unless a solvent-based clean-up treatment was used. Buyers often ask for the solvent panel anyway.

Translator’s note: under Thai rules, you may use only pesticides registered with the Department of Agriculture (กรมวิชาการเกษตร), and only as the label directs. See What You May Legally Spray Under Thai GACP. A buyer’s limits may still be stricter, including the 0.01 mg/kg default. Keep a spray record for every batch: product, active ingredient, date and dose. With that record, you can ask the lab to include each substance you actually used. This makes it far less likely that a residue first shows up in the buyer’s test.

What to do: turn this list into a table. Add one column for “required by buyer” and one for “covered by lab scope”, and fill it in before you sign.

8. The final check before you send a certificate

Before you send a COA to a buyer, check that it:

  • names the laboratory and its accreditation scope
  • names the analytical method used for cannabinoids
  • reports acid and neutral forms separately (for example THCA and THC), with the total calculated
  • carries the batch or lot number that matches the labels, the packing list and the export permit
  • states loss on drying and, separately, water activity
  • covers pesticides, the four elemental impurities (arsenic, cadmium, lead, mercury), aflatoxin B1 and microbiology for the correct route of use
  • declares any decontamination treatment

The batch-number match is worth repeating. A mismatch is the most common paperwork reason for rejection, and it has nothing to do with the quality of the flower.

Translator’s note: give each batch one number at harvest. Use that number on every record: harvest log, drying log, lab sample form, labels, packing list and export permit application. Then a buyer or inspector can trace every document back to the same batch without any doubt.

What to do: before you send any COA, lay the COA, labels, packing list and export permit side by side and compare the batch numbers character by character.

Share what you know

If a Thai laboratory has issued a COA that a European or Australian buyer accepted without re-testing, please post the laboratory’s name and its accredited scope below this topic. That information would help other exporters more than any amount of specification detail. If every buyer you have worked with re-tested on arrival, that is useful to report too.

Related reading: the topic on reading a COA, linked at the top of this article.

References (Part 2)

This article is reference information for readers who operate legally in their own jurisdictions. It is not regulatory, laboratory or legal advice. Figures marked “reported” in Part 1 come from published extracts and summaries of the monographs, and the decontamination figures are indicative. Check current limits against the current edition of the relevant pharmacopoeia and regulator guidance, and confirm any laboratory’s scope directly before relying on it.