CBN, or cannabinol, is a mildly psychoactive minor cannabinoid that is found in trace amounts in cannabis. It is actually found in more abundance in aged cannabis. If cannabis is exposed for a prolonged period of time to air or UV light, the THCa, or tetrahydrocannabinolic acid, in it will degrade into cannabinolic acid (CNBa) which then transforms into CBN in a chemical reaction that releases a carbon atom and CO2, called decarboxylation.
Some claim that CBN has a strong sedative effect, especially when used in conjunction with THC. This is why some people say that older cannabis or poorly stored marijuana that has been exposed to air and light is likely to make you more chill.2
This observation that older cannabis can make you drowsier than fresher cannabis might have been first discovered by marijuana users who found an old stash. But now that people believe this to be a reality, based on their anecdotal experience, some people now age their cannabis purposefully, like one might age a cigar or a bottle of wine, to nurture this potential effect. Some cannabis connoisseurs have also noticed this CBN effect from cannabis that was harvested a week or so after the intended harvesting date. Again, these experiences are anecdotal and should be taken with a grain of salt.
Here’s something a little more rooted in the science: a 1999 study by the United Nations Office of Drugs and Crime reported that THC content in a tested cannabis sample dropped to half of its original potency after four years. As the THC oxidized over time, it converted to CBN. Researchers suggest that CBN has one-quarter the potency of THC.3