Stored Saliva Cannabis Samples: Why a Two-Month Recommendation Can Coexist With Three-Month THC Data

A study found generally favorable THC stability in refrigerated oral-fluid samples for three months, yet recommended no more than two months when interpreting a broader cannabinoid panel. The difference reflects which analytes and acceptance criteria are being considered.

Authentic samples in a specified device

Researchers collected oral fluid with the Quantisal device after controlled cannabis smoking. Samples from seven frequent and eight occasional users were pooled separately for each participant and tested initially and after one, two and three months at 4°C.

The study evaluated THC, THC-COOH and several minor cannabinoids. It did not measure deterioration in every possible saliva container, buffer or shipping condition. The collection system was part of the tested workflow.

Some three-month results fell outside stability criteria

THC remained within the study’s stability range except for one participant’s result just below 80% of baseline at three months. Some THC-COOH and minor-cannabinoid measurements also fell below the criterion at that point.

Several occasional-user samples had analytes below quantification at baseline, leaving fewer evaluable samples for those compounds. A compound that could not be quantified initially does not provide an informative percentage-retention experiment.

A panel recommendation is not a single-analyte claim

The authors recommended a maximum two-month refrigerated interval to support the full panel, while describing the more favorable three-month THC observations separately. Those statements are compatible. The longer result should not be presented as a guarantee for all analytes.

Likewise, a result near an acceptance boundary does not justify an exact retrospective correction for a particular case. The study showed variability among participant pools rather than a single universal degradation factor.

What a reanalysis opinion needs

Obtain the device, buffer, actual temperature record, time to analysis and analyte-specific laboratory validation. The evidence is particularly relevant to delayed confirmatory or defense-requested reanalysis, but it does not certify specimens stored under different conditions. Stability concerns whether a concentration is preserved; it does not establish what that concentration meant for impairment when collected.

For context, see our discussion of THC concentrations and the separate question of impairment.

Primary research

Karl B. Scheidweiler and colleagues. Long term stability of cannabinoids in oral fluid after controlled cannabis administration. Drug testing and analysis (2016). DOI: 10.1002/dta.2056.