"Lettucene" was a trade name for a solid extract from wild lettuce,
Lactuca virosa. It was most likely prepared the usual way, by making a tincture with ethanol and then evaporating. The active sedating ingredients are probably sesquiterpene lactones including lactucerin, lactucin and lactucopicrin. Polyacetylenes (polyines) are also present, some of which may have cannabinoid activity.
Garden lettuce,
Lactuca sativa, has a similar sedative effect when consumed in quantity, some varieties being stronger than others. I got a decent sedative effect by eating three 'Little Gem' baby Romaine lettuces one time (in an act of desperation when pot supplies were low)! The main thing is to consume as much of the stem as possible as the actives are present in greatest quantity in the stem latex. Of course, the nervine effect of magnesium content of the lettuce shouldn't be overlooked in this single anecdotal account.
The crude drug substance from edible lettuce is called
thridax; this is prepared by steaming the expressed juice of the plant. The dried latex of the wild lettuce is known as
lactucarium (PT:
Lactucário).
As far as getting a single, pure, active ingredient goes you would probably have to use chromatography. It may well be that the activity is reliant on a synergy of multiple compounds; the efficacy of lettuce of either variety is unreliable and Lactuca virosa might rightly be regarded as significantly toxic.
This paper is a relevant read:
https://doi.org/10.1016%2Fj.jep.2006.03.003Noteworthy was:
Quote:An analgesic potency of lettuce opium extracts was studied
by Funke et al. (2002), and a distinct inhibition of enkephali-
nase activity in a concentration-dependent way was found. The
lettuce opium gathered from 1-year plants showed a more pro-
nounced inhibition of the enzyme than that from biannual plants.
Opioid receptors were not affected by the extracts.
Further studies to identify enkephalinase inhibitors in Lac-
tuca virosa seem to be worthwhile.
We could surmise that lettuce works by slowing or stopping the breakdown of endogenous painkiller peptides.
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― Jacques Bergier, quoting Fulcanelli