Color tests: Marquis test—slow/weak ‘salmon orange’ (pink, orange red); Mecke’s reagent—dark orange -> dark purple-ish orange; sodium nitroprusside—cherry red colour [Zimmerman 2001]
Disposition in the Body: delta9-THC is absorbed from the gastrointestinal tract but absorption is slow and irregular. However, THC can be measured in plasma within seconds after inhalation of the first puff of marijuana smoke. THC is lipophilic and is widely distributed in the body. It is oxidised to the active metabolites 11-hydroxy-THC (aka 11-OH-THC) and 8b-hydroxy-THC by an hepatic cytochrome P450 enzyme. The inactive substances 8a-hydroxy-THC and 8a,11-dihydroxy-THC are also formed. 11-Hydroxy-THC is further oxidised to 11-nor-9-THC-carboxylic acid (THC-11-oic acid), and many other polar mono- and dicarboxylic acids are formed; these are conjugated with glucuronic acid to a variable extent. Enterohepatic circulation of metabolites may occur. Up to ~25% of a dose is excreted in the urine in 3 days, mainly as 11-nor-THC-9-carboxylic acid glucuronide, together with the other carboxylic acids in free and conjugated form. THC-O-glucuronide has also been detected in urine. The major excretion route is via the faeces, up to around 65% of a dose being excreted in 5 days, mainly as 11-hydroxy-THC and the carboxylic acids in conjugated form. THC metabolites have been detected in urine for up to 12 days following a single oral dose. It crosses the placenta and is distributed into breast milk.
Bioavailability. After ingestion, ~6–20%. During smoking, ~18–50%.
Therapeutic Concentration. After 11 subjects had smoked 11.6 to 15.6 mg (mean, 13.0) of THC from a cigarette over a period of 5 to 7 min, peak plasma concentrations of 0.03 to 0.12 mg/L (mean, 0.08) of THC were observed within 3 min after termination of smoking; the concentration fell rapidly to 0.003–0.01 mg/L (mean, 0.007) at 1 h and to 0.0006–0.003 mg/L (mean, 0.0016) at 4 h, after smoking. When 20 mg THC was given orally to the same subjects, peak plasma concentrations of 0.004–0.01 mg/L THC were produced between 60 and 300 min after ingestion [Ohlssonet al.1980]