After oral administration, lysergic acid diethylamide (LSD) reaches peak plasma concentrations of 1.3 ng/mL (100 µg dose) and 3.1 ng/mL (200 µg dose) within about 1.5 hours, with a plasma half-life of 2.6 hours. Subjective effects last 8 to 12 hours depending on dose, and peak effects occur around 2.5 to 2.8 hours after ingestion. A close relationship exists between LSD concentration and subjective response within individuals, but no correlation was found between plasma levels and effects across different people at peak concentration. The effects are related to changing plasma concentrations over time, without evidence of acute tolerance.
A new microflow liquid chromatography tandem mass spectrometry method was developed to quantify LSD and its metabolites in human plasma, enabling detection limits of 0.01 ng/mL and separation within three minutes. In a controlled pharmacokinetic study, elimination half-lives of iso-LSD (median 12 h) and LSD metabolites (median 9, 7.4, 12, and 11 h for oxo-HO-LSD, HO-LSD, HO-LSD-gluc, and nor-LSD, respectively) exceeded that of LSD (median 4.2 h). However, screening for these metabolites to extend detection windows in plasma is not constructive because their concentrations are very low.