Cannabinol (CBN) is the degradation cannabinoid from Δ-9-tetrahydrocannabinol (THC). Recent years have seen interest in CBN increase due to low intoxication effects and certain potential benefits.  Few cannabis chemovars emphasize this cannabinoid naturally although it may be slightly elevated in overripe flowers. When the main goal is to decrease THC and increase CBN, extractors and processors may implement different techniques to convert THC to CBN.
The most common and obvious strategy beyond natural aging is to apply heat. According to Wang et al , “Δ-9-THC itself readily oxidizes to cannabinol (CBN) with oxygen and light during the decarboxylation process.” A different study published in 2005 found that this oxidation occurred above 150° C (302° F) given a 15-minute decarboxylation period.  The typical decarb process employs lower temperatures and longer times to avoid this conversion and preserve Δ-9-THC; amping up the temperature may thus prove useful for CBN seekers. However, using a vacuum oven mitigates this conversion. 
An active patent was granted earlier this year that describes heat/decarboxylation as a “method for increasing cannabinol content in a lipid-based extract of cannabis.” The first step is to deliberately vaporize Δ-9-THC at 160° C, and the second step is a heating conversion of remaining Δ-9-THC to CBN at 140-160° C for up to 60 minutes. The implication is that such conversion can be used to remediate hemp with THC concentrations that exceed federal legal limits.
Light also degrades cannabis and facilitates conversion of THC to CBN. Theoretically, intense light exposure might also prove useful. Ultraviolent light is mentioned as an alternative to heat as the second step in the aforementioned patent although details are not provided.
Pollastro et al  took a different approach to THC-CBN conversion, namely iodine treatment. The authors report that “refluxing in toluene with two equivalents of iodine was sufficient for the spot-to-spot conversion of Δ-9-THC into CBN. After workup and chromatographic purification, a rewarding 70% yield was obtained.” Interestingly, iodine also converted cannabidiol (CBD) and acidic precursors (tetrahydrocannabinolic acid and cannabidiolic acid). The authors speculate that the aromatization reaction involves the formation of acidic molecules that facilitate the cyclization of CBD into THC. This technique is therefore applicable for CBN from intoxicating and non-intoxicating cannabis varieties. 
Often considered mere evidence of old cannabis, CBN may soon become a minor cannabinoid of prominence. Potency (in terms of intoxication due to agonist activity at cannabinoid receptors) has been estimated from 10 to 25% compared to THC. [1,5] Among its various potential therapeutic properties, CBN is most popularly associated with sedative effects. Converting THC and other cannabinoids to CBN may offer a way for product creators to diversify and meet newfound demand.
If you were to look at a ripe cannabis flower under a microscope you would see hundreds of little opaque mushroom-like structures called trichomes; it is in these structures that the cannabinoids (the chemicals that cause cannabis’s effects) are found. THC (tetrahydrocannabinol) is the most famous of the over 100 cannabinoids that have been isolated in laboratories and is the chemical responsible for the psychoactive properties of the cannabis plant. Under prohibition, growers and consumers generally rate the quality of a cannabis plant based on it’s THC content; the higher the content, the better the plant. THC is not a stable chemical and can be converted into another cannabinoid known as cannabinoid (CBN); before we discuss CBN, however, we should discuss THCa.
THC begins its life as THCa (tetrahydrocannabinolic acid); a non-psychoactive cannabinoid whose benefits we are just beginning to learn about. THCa is converted into THC through either time or heat which explains; when we smoke or vaporize cannabis we convert the THCa into THC through the heat that we are applying to it. The first step most cannabis bakers take when creating edibles is to “decarb” the cannabis by baking it in an oven before mixing it with butter (or another cooking fat such as oil) to convert the THCa into THC; if this step is skipped than the edibles will not have the euphoric effects that most consumers desire. Most cannabis processers will stop when the THCa becomes THC but we can take the process of converting THCa into THC a little further and create a third cannibinoid; Cannabinol, aka “CBN”.
Cannabinol is essentially THC that has degraded either through heat, time, or some combination of the two. Ever smoke old flowers that weren’t stored properly and found yourself immediately tired? That is the effect of CBN; rather than getting high and paranoid you just get sleepy and lethargic. The only way to smoke CBN is through old flowers which is why tinctures and edibles are the preferred methods of consumption for this cannabinoid. The wait for THCa to convert to CBN without combustion or vaporization can take years; rather than wait for for so long we will use our oven to decarb our harvest.
Decarboxylation for CBN
Decarboxylation is the first step in creating edibles or tincture and is done to “activate” the THC (convert THCa into THC). Normally we decarb cannabis by placing the flowers in an oven for 30-45 minutes at 250ºF; THCa (tetrahydrocannabinolic acid, a non-psychoactive substance) is converted into THC (the psychoactive substance most cannabis users are interested) through the heat of your oven. If we decarb our cannabis at a higher temperature and for a longer period, the THC will break down into CBN (the relaxing cannabinoid we want). Place your cannabis (you can use flowers or trimmings) in oven bags in a preheated oven for 320º for an hour and a half and be prepared to stink up the house as you will be slowly burning the cannabis; you may want to do this late at night if you have neighbors living close by. Remember that you are converting THC into CBN; you can control the balance between the two cannabinoids by adjusting the temperature and bake time to suit your needs.
Processing (Tincture, Edibles)
Once you have pulled your oven bags filled with sativa flowers out of the oven let them cool for a bit and take a look. Does it look burnt? Does it look like it was left outside for a few weeks? Is the smell overwhelming? You did it right. As horrifying as it is to see a bunch of cannabis flowers burnt in the oven, this is the CBN-rich concoction we are looking for. You will not want to smoke or even vaporize this stuff, instead you will use it in your favorite butter, oil, or tincture recipe.
Strains for CBN
Because we decarb our flowers at such a high temperature, most of the terpenes will have been burned off which means it doesn’t really matter which strains we use specifically so long as it has a high yield and a high THC count. Blue Dream, Dream Queen, and Sour Diesel are all great high yield, high THC sativa that are easy to grow outdoors so they all make great candidates for creating CBN. Because the effects of CBN are so different than THC, one can use the same plant to create a number of effects by adjusting your decarb time and temperature; it’s like having multiple strains in one easy-to-grow plant! Relax, enjoy your new favorite cannabinoid; sativa can be sleepy too!