THCA to THC Conversion With Heat: Temps and Times

THCA to THC Conversion With Heat

THCA converts to THC when heat removes a carboxyl group from the molecule. The reaction is decarboxylation. It starts near 180°F (82°C). Most conversion happens between 220°F and 250°F (105°C to 121°C) over 30 to 60 minutes. THCA has no psychoactive effect. THC does.

The Chemistry

THCA is tetrahydrocannabinolic acid. Its molecular weight is 358.47 g/mol. THC weighs 314.46 g/mol. The 44 g/mol difference is one carbon dioxide molecule. Mass drops by 12.3 percent when the reaction completes. One gram of THCA yields 0.877 g of THC at full conversion. The reaction needs no catalyst. Heat supplies the activation energy.

Time and Temperature

180°F (82°C): conversion starts. Rate is slow.
220°F (105°C): 30 to 60 minutes for flower.
240°F (115°C): 30 to 40 minutes.
250°F (121°C): 27 minutes in published lab data.
315°F (157°C): boiling point of THC. Vapor forms.
Above 300°F (149°C): THC oxidizes to CBN. Yield falls.

Exact numbers change with the sample. Moisture, particle size, and starting THCA content shift the curve. Published studies report peak conversion between 70 and 90 percent under lab conditions.

Heat in Daily Use

A lit joint reaches 600°F to 900°F (315°C to 480°C) at the cherry. THCA at the tip converts in seconds. Some THC burns off in the same zone. A dry herb vaporizer runs at 315°F to 430°F (157°C to 221°C). Conversion there is partial, and leftover material still holds THCA. Dabbing uses a surface above 500°F (260°C). Conversion is near complete, with some loss to pyrolysis.

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Storage and Slow Conversion

THCA converts without added heat. The reaction runs at room temperature over months. Light, air, and warm storage speed it up. Flower kept at 70°F (21°C) for a year loses part of its THCA. Cool, dark, sealed storage slows the change.

Total THC on a Label

Labs report THCA and THC on separate lines. Total THC uses one formula: THC + (THCA × 0.877). State regulators use this value for limits and labels. A flower sample with 20 percent THCA and 1 percent THC reads 18.5 percent total THC.

What Heat Does Not Do

Heat does not turn CBD into THC. THC and CBD come from different precursors. Heat does not add cannabinoid mass to the plant. It removes CO2 and lowers weight. A freezer at 0°F (-18°C) stops conversion for practical purposes.