Both cannabinoids and terpenes play a role in the side effects of cannabis, and it turns out these compounds are quite susceptible to the elements! Generally speaking, heat, oxygen and sunlight are all detrimental to the shelf life of our beloved cannabis. THC will naturally decompose to CBN over time with the help of light and air, for example, and it’s general lore that CBN can make you sleepy. So what else is happening to our cannabis as it ages? Should we be overly concerned with fresh consumption? A general discussion of stash dynamics and how terpene and cannabinoid profiles change over time follows!
When analyzing the potential side effects of a particular strain, both the terpenes and cannabinoids must be taken into consideration due to the entourage effect. This is the synergistic effect that terpenes and cannabinoids have on the endocannabinoid system when combined. That old ganja you found under your bed may have different psychological effects than a few months ago because 1. the entourage effect and 2. the change in cannabinoid and terpene profiles over time.
Terpene Profiles Change Over Time
The most common terpene in cannabis is myrcene. It represents over 20% of the terpene profile in modern commercial cannabis strains. Myrcene can also be found in hops and beer (mangos too!) and generally has a peppery, earthy, spicy balsam-type fragrance. Although there is little scientific evidence to back it up yet, myrcene rich foods such as lemongrass have been used as a sleep aid for centuries. Myrcene may even have muscle relaxing properties at high concentrations.
Myrcene also has a particularly high boiling point when compared to some of the other terpenes, so it tends to hang around. The top four terpenes found in all cannabis are myrcene, caryophyllene, alpha-pinene and limonene. We can determine based on boiling points and vapor pressures which terpenes will hang around the longest. The lower the boiling point and the higher the vapor pressure, the easier it is for the terpene to evaporate away.
- Terpene Boiling Pt Vapor Pressure
- Myrcene 332.6 °F 1.69 Torr
- Caryophyllene 473.5 °F 0.02 Torr
- Alpha-Pinene 314.3 °F 3.57 Torr
- Limonene 348.8 °F 1.13 Torr
In this lineup, we’d expect that pleasant scent of pine to fade most quickly, because alpha-pinene has the lowest boiling point. We’d also expect caryophyllene to hang around the longest because it requires the most energy to boil and evaporate away. Caryophyllene has been shown to have anti-anxiety effects as a CB2 (ECS receptor) agonist. This points to the complexity of the entourage effect, since terpenes also bind to our ECS receptors! And perhaps helps explain why older weed makes us sleepy.
Stash Dynamics: Decomposition of THC
The primary psychoactive component of cannabis, THC, is what causes the feeling of euphoria. Over time, weed becomes less potent as THC degrades to CBN, lessening the psychoactive effects. There are claims that CBN is the sleepy-time cannabinoid, but that hasn’t yet been proven scientifically. Regardless, over time the THC in cannabis does degrade to CBN, and does appear to make users more sleepy!
There is not a lot of readily available literature on the way THC decomposes to CBN. It seems generally accepted that light and oxygen play a key role, however the exact mechanism is yet to be elucidated. Typically dehydrogenation, or loss of H2, is an energetically uphill process because it takes a lot of energy to break carbon hydrogen bonds. However the final product, CBN, has an additional aromatic ring formed at the reactive site, which lowers the energy of the overall process significantly. (Chemistry nerds – did you know water speeds up decarboxylation?)
We’re very interested to see if and when a mechanism is worked out for the oxidation of THC to CBN. The fact remains, we need to keep our weed away from oxygen (jar it up!) and light (put it away!) when it’s not in use if we want to really keep things fresh. This will also keep the side effects more reliable over time.