Screening for residual solvents is required only for cannabis products made using a solvent-based extraction method. The amount of residual solvent left in a cannabis concentrate must be shown to be below the allowable limit in milligrams, which varies for each applicable solvent.
Concentrated cannabis products made using a solvent must be purged at the end of the extraction process. Trace amounts of the solvent used can remain even after purging, and high concentrations of certain solvents can be harmful if consumed. Screening products for residual solvents helps ensure consumer safety.