It is generally accepted among growers if you allow a flowering cannabis plant to more fully develop the trichomes to become more amber. Trichomes, the oil glands, begin with clear oil, become cloudy and finally amber. Every grower has their own protocols as to when to harvest, but in general, early amber is a good time to harvest the plant.
If one allows the trichomes to turn darker amber, the flowers become more sedating when smoked or ingested. Two things happen in those last few weeks. CBN (Cannabinol) levels rise if the plant is left long enough, AND the level of the terpene, Myrcene, increases.
The Myrcene test was done by myself and a group of local licensed growers. Two years ago we picked 1/3 of a crop when terpenes were clear, another 1/3 fully cloudy and the final 1/3, fully amber. Myrcene levels went up with further plant maturation. We have seen this in a number of other situations.
With regard to CBN or Cannabinol, truthfully, we rarely see very much. Why? THC oxidizes to CBN with time, sun and heat. Generally, leaving cannabis to dry in the sun and heat oxidizes, converts or degrades THC to CBN.
So, is it the sedating Myrcene levels climbing or is it the CBN? I am sure, as is usually the case, it is both, but I certainly believe it is nearly all Myrcene and other terpenes that cause the majority of the effect.
I found an interesting article from 1975, which clearly found in a SMALL study group, that CBN could only account for a very minor amount of the sedation.
My current feelings, although I am open to any new data or ideas for sure, are that terpenes are responsible for the added sedation of crops harvested later. If we begin studying this more, we can probably create new oil extracts FROM THE SAME PLANT, JUST BY HARVESTING LATER.
The interaction of delta9-tetrahydrocannabinol (delta9-THC) and cannabinol (CBN) was studied in man. Five male volunteers were given placebo, 50 mg CBN, 25 mg delta9-THC, 12.5 mg delta9-THC + 25 mg CBN, and 25 mg delta9-THC + 50 mg CBN (orally). Administrations were spaced 1 week apart. With physiological measures, delta9-THC produced an increase in heart rate while CBN did not. When combined, no change of the delta9-THC effect occurred. No changes occurred on the electrocardiogram, blood pressure, or body temperature. With psychophysical measures no changes occurred in pain thresholds or skin sensitivity as a function of drug treatment. In time estimates of the passage of 1 minute, delta9-THC alone produced underestimates of the passage of 1 minute and CBN alone had no effect. In combination the two drugs had a tendency to produce significant overestimates and underestimates of the passage of 1 minute. On a 66-item adjective-pair drug reaction scale, the volunteers reported feeling drugged, drunk, dizzy, and drowsy under the delta9-THC condition, but not under the CBN condition. With combined drug treatment, volunteers reported feeling more drugged, drunk, dizzy, and drowsy than under the delta9-THC condition alone. None of the drug treatments produced significant changes on other items which included items on perception, emotion, cognition and sociability. It appears that CBN increases the effect of delta9-THC on some aspects of physiological and psychological processes, but that these effects are small and cannot account for the greater potency which has been reported when plant material is used.