How to read a cannabis COA (lab test)

A certificate of analysis (COA) is the lab report behind a cannabis product. Every legal product in Canada is tested before it reaches a shelf, and the COA is where those results live. Learning to read one means you know what you’re actually buying, not just what the front of the package claims.

What a COA shows

• Cannabinoid content: THC and CBD, plus minor cannabinoids like CBN and CBG. Watch for two THC numbers. Raw cannabis holds most of its THC as THCA, which only converts to active THC when heated, so the Total THC figure accounts for that conversion. That’s the one that reflects real strength. See what THC percentage means.
• Terpene profile: the aromatic compounds (myrcene, limonene, pinene, linalool and others) that shape a product’s smell and character. Not every COA lists them; the better ones do. See common terpenes.
• Contaminant screening: pass or fail results across several categories:
  • Pesticides: residues from cultivation, tested against strict limits.
  • Heavy metals: lead, arsenic, cadmium, and mercury, which plants can draw up from soil.
  • Microbials: yeast, mould, and bacteria such as E. coli and Salmonella.
  • Residual solvents: for extracts and concentrates, any leftover butane or ethanol from processing.
  • Mycotoxins and moisture: mould byproducts, plus a water-activity reading that flags mould risk.
• Batch and lab details: the batch or lot number, the testing lab, its accreditation, and the test date.

How to actually read one

1. Match the THC and CBD to the label. Legal potency claims have to fall within a set tolerance of the lab result. A large gap is a warning sign.
2. Confirm every contaminant line says “pass.” A single fail should keep a product off the shelf. This is the safety layer the illegal market cannot offer.
3. Check the lab and the date. A named, accredited lab and a recent test date matter. An anonymous report is a red flag.
4. Tie it to your product. Legal packaging carries a batch or lot number, often with a QR code, that should lead to the matching COA. If the numbers don’t line up, the report means nothing.

Where to find one

For legal Canadian products, the potency is printed on the label, and the full COA is usually available through the producer’s or your province’s official channel, often via a QR code or a batch lookup. If you bought from an unlicensed source, there’s usually no real COA to find, and any document handed over cannot be verified.

Why it matters

The single biggest safety advantage of legal cannabis is independent lab testing, and the COA is the proof. A seller who cannot or will not show one, or who shows a report that doesn’t match the product, is telling you something worth listening to.

Sources

• Health Canada, Cannabis testing requirements
• Health Canada, Good production practices for cannabis