THCA vs THC: The Legal Difference, and Why It Ends in December

What is the legal difference between THCA and THC?

THC is the compound the law names, and THCA is its raw acid form, which turns into THC when heated and which the statutory hemp definition has not counted until now.

The statute measures one compound. 7 U.S.C. 1639o defines hemp as cannabis with a delta-9 THC concentration of not more than 0.3 percent on a dry weight basis. THCA is a different molecule, so it sits outside that number. The Controlled Substances Act then excludes hemp from the definition of marijuana. Sellers read that wording as covering a flower that passes the delta-9 test, however much THCA it holds.

Federal production is a different story. USDA’s rules already test growers on total THC, THCA included (details below). So the delta-9 wording shapes the retail market, and the plant is measured on total THC before harvest.

Status as of 2026-10-26: this is the wording in force. It ends on 11 December 2026, when the definition becomes total THC. The rest of this page shows how the old test works, how the new one is calculated, and what to check on a lab report. Full state picture: is THCA legal.

Why is THCA legal but not THC?

THCA is sold as hemp because the statutory definition caps delta-9 THC at 0.3 percent and sets no cap on THCA.

The chain has three links. First, hemp is outside the federal marijuana definition (21 U.S.C. 802(16)(B)). Second, hemp is defined by delta-9 THC at 0.3 percent or less (7 U.S.C. 1639o). Third, a flower can hold very little delta-9 THC and a great deal of THCA when it is sold. Sellers conclude that it passes the second link, so it is hemp, so it is not marijuana.

The Congressional Research Service (update of 28 September 2026) notes that some have read the 2018 farm bill this way, because delta-9 is not the only THC compound in cannabis. It also ties authorised cultivation and sale to USDA regulations and state rules. Congress rewrote the definition in 2025. The effective date is the part most pages skip.

How is THCA legal when it becomes THC in a pipe?

Sellers rely on delta-9-only lab reports at retail, while federal production testing already includes THCA and happens before harvest.

The conversion is real and fast. A 2016 study by Wang and colleagues heated cannabis extract in a vacuum oven at 80 to 145 degrees Celsius for up to 60 minutes. THCA did not fully convert below 100 degrees in that time. It approached zero after 30 minutes at 110 degrees, 9 minutes at 130 degrees and 6 minutes at 145 degrees. The authors report complete conversion to delta-9 THC with no by-products. The study used extract, not retail flower, so the times show the chemistry, not what happens in a pipe or vaporiser.

USDA already measures this way. Its hemp production rules define total THC as the value determined after decarboxylation, from the sum of THC and THCA. Testing under 7 CFR 990.25 must consider the potential conversion of THCA into THC, and sampling happens no more than 30 days before harvest (7 CFR 990.24). The retail wording in the statute never used that figure. A delta-9 result on a retail jar therefore does not show compliance with production rules or state law.

How do you work out total THC from a lab result?

Total THC equals delta-9 THC plus THCA multiplied by 0.877, because THCA loses carbon dioxide when it converts.

The 0.877 factor adjusts for mass lost as CO2. A 2026 paper on hemp flower states the formula as Total THC = delta-9 THC + THCA x 0.877 and explains the factor the same way. Here are three hypothetical results, all on a dry weight basis. The examples assume no other THC isomers or similar-effect cannabinoids are present.

Sample	Delta-9 THC	THCA	THCA x 0.877	Total THC	Passes delta-9 test (0.3%)?	Passes total-THC test (0.3%)?
A: THCA flower	0.20%	24.00%	21.05%	21.25%	Yes	No
B: low-THC hemp flower	0.10%	0.30%	0.26%	0.36%	Yes	No
C: CBD-type hemp flower	0.05%	0.20%	0.18%	0.23%	Yes	Yes

Sample A works out like this: 24.00 x 0.877 = 21.048, and 21.048 + 0.20 = 21.248, which rounds to 21.25 percent. A 3.5 g jar of it holds about 3,500 mg x 0.2125 = 744 mg of total THC. The container exclusion for final products is more than 0.4 mg, so that jar is about 1,860 times the cap. Percentages on a lab report are dry weight, so the true figure for a jar with moisture is a little lower. The conclusion does not change.

Sample B shows the sting in the new test. Its delta-9 figure is within the limit, and THCA pushes it over. Only sample C passes both tests.

The statute counts total tetrahydrocannabinols, and the container exclusion also covers cannabinoids with similar effects. If a product holds other THC isomers or those compounds, the two-number sum understates the total.

What is the difference between the old delta-9 test and the new total-THC test?

The old definition names delta-9 THC only, and the new one counts total THC including THCA and adds a cap of 0.4 mg per container for final products.

	Current definition	New definition
Law	7 U.S.C. 1639o(1), 2018 farm bill text	7 U.S.C. 1639o(1) as replaced by section 781 of P.L. 119-37
What is measured	Delta-9 THC concentration	Total tetrahydrocannabinols concentration, including THCA
Limit	Not more than 0.3 percent, dry weight	Not more than 0.3 percent, dry weight
Final products	No container limit	Excluded above 0.4 mg combined total per container of total THC and similar cannabinoids
In force	Until 10 December 2026	From 11 December 2026 (P.L. 119-103, section 2019)
If a product fails	Not hemp, so marijuana under 21 U.S.C. 802(16)	Excluded from hemp; the CRS says such products are treated as marijuana

Sources for the new column: Cornell’s copy of the Code and the CRS report. The CRS defines a container as the innermost packaging in direct contact with the product for retail sale. The delay law is short: until 11 December 2026 the 2025 amendments apply only to two product types, those in paragraphs (1)(C)(ii)(I) and (1)(C)(iv)(I) of the statute. The CRS describes the first of those as cannabinoids the plant cannot naturally produce, which starts on 12 November 2026. For that date and the product-by-product split, see when the hemp ban takes effect.

Is THCA federally legal right now?

As of 2026-10-26, sellers market THCA flower as hemp when its delta-9 THC is 0.3 percent or less, and the definition changes on 11 December 2026.

The effect of the new test is the table above. Sample A, a hypothetical high-THCA flower, goes from marketed-as-hemp to outside the hemp definition. Any covered gummy or drink container with more than 0.4 mg of the specified combined cannabinoids exceeds the container limit. Congress delayed the change once, in P.L. 119-103 of 2 September 2026. No enacted law moves the 11 December date. Only a new act of Congress could.

FDA was told to publish detail on the container rules. As of the CRS update of 28 September 2026, it had not. How the definition applies to a jar of flower follows the statute text, and no court has ruled on it yet. For the effect on states with legal weed, read will the hemp ban affect legal states.

Does state law change the answer?

State law can make THCA illegal even while the federal definition allows it, so the federal test is only the starting point.

Texas is the plainest case. Its health department’s rule 25 TAC 300.101, effective 31 March 2026, defines total THC as the sum of THC isomers and THCA (THCA x 0.877 plus THC), so THCA flower is measured on total THC there today. See is weed legal in Texas. Florida limits hemp to 0.3 percent “total delta-9” THC and lists acids among the covered forms (Fla. Stat. 581.217). Marijuana sold under a state licence is outside the hemp definition altogether. For other states, start from the guides.

What should you check on a lab report before 11 December?

Check which THC figure the report uses, how big the container is, and whether your state allows the product, in that order.

1. Find the line that reads “total THC” or “THC + THCA x 0.877”. A report that lists delta-9 THC alone cannot show whether you pass the new test.
2. Do the sum. Multiply THCA by 0.877, add delta-9 THC, and compare with 0.3 percent for plant material.
3. For a finished product, convert to milligrams per container and compare with 0.4 mg.
4. Look up your state’s hemp rules. Federal law sets one layer.
5. If you hold stock or face a charge, talk to a cannabis lawyer before 11 December.