The Shelf Life of Cannabis & Effects of Light and Air

    by Adam Merckle

    Exploring the Effects of Light and Air

    It is a well-known fact that cannabis needs light and airflow to grow, but what about after it’s been harvested and cured? What happens when that eighth of flower sits on a dispensary shelf for six months or a year?

    Most Cannabis products available in dispensaries today usually have an expiration date on the label, but why? Does it go bad? Why are we told to keep our cannabis flower away from the light?

    Let’s dive right in and explore the science behind air and light and what it does to our Cannabis flower.

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    What Science Has Found

    A few studies have been conducted regarding the stability or shelf life of THC and have helped shed some light on how cannabis should be packaged and stored.

    The scientific community first became aware of light degrading THC because of a study conducted in 1971. The study concluded that; to best preserve THC, cannabis should be stored in nitrogen instead of oxygen and away from ultraviolet light.

    In 1976, another study determined that exposure to light (not direct sunlight) was the number one factor in Cannabinoid loss over time. This study also showed that THC loss from light exposure does not lead to an increase in the Cannabinoid CBN or Cannabinol, but rather air oxidation in dark conditions does.

    A more recent study at the University of Mississippi in 1999 showed that over one year, THC levels in cannabis samples stored in a dark vault reduced by 16.6% of their original amount and as much as 41.4% after four years. Scientists found that; at an average loss rate of 1.3% per month, most cannabis smoked within one year of being harvested should be relatively close to ideal freshness if kept under proper conditions.

    So, What Does All That Mean?

    The two main takeaways from these studies are that THC will do one of two things when it degrades. Exposure to oxygen in dark conditions will turn THC into CBN over time, but exposure to ultraviolet light can destroy THC. So, what does that mean for the stash of bud you lost two years ago, or the cannabis sitting on dispensary shelves in clear jars, or how about that bud that just endured a two-hour-long photoshoot for High Times?

    If you happen to find that old stash of bud from last 4/20 buried deep in your sock drawer, go ahead and smoke it, but be prepared to take a nap! In those dark conditions, the THC will be broken down into CBN and be apparent from the clear-milky trichomes turning a dark amber color.

    While the effects of CBN are still being studied, Steep Hill Labs has said that 5mg of CBN is equal to 10mg of Valium, and therefore if you smoke cannabis left in a drawer for an extended length of time, it may make you feel more tired than it would otherwise.

    But What About My Camera Flash and Display Lights?

    There have been studies conducted on the effects of fluorescent light and flash photography on works of art, but not many regarding its impact on cannabis. From the studies conducted on THC stability, we can assume that too much exposure to high-intensity light will affect the stability of THC.

    Most light humans can see with the naked eye is classified as non-ionizing radiation on the electromagnetic spectrum and is therefore harmless to humans and cannabis. Ultraviolet or UV light is right on the line between ionizing and non-ionizing, and most compact fluorescent lamps or CFL bulbs produced today emit a small amount of UV light.

    When it comes to modern camera flashes and LED display lights, the jury is still debating how they can affect cannabis. If you’re displaying your top-shelf bud under bright LED lights for days on end, there will most likely be some loss of THC. On the other hand, a few minutes or even an hour of exposure to camera flashes or bright LED display lights probably won’t affect the potency of your cannabis too much.

    Personal Research

    Being a cannabis connoisseur and a science fanatic, I decided to research this. I regularly review cannabis, which involves taking quite a few pictures of it under magnification and about an hour of exposure to bright LED lights.

    I started paying attention to the trichomes and how they look, indicating THC degradation. I even left a bud under a MasonBrite display jar for thirty minutes straight and didn’t notice any change in the appearance of the trichomes or potency compared to the rest of the batch. Another bud, I left under a heat lamp for a week, and there was a visible difference in the trichomes and the effects I felt afterward; the trichomes were dark amber, and I slept like a baby.

    So, What Is the Verdict?

    The three things that can affect the potency and quality of cannabis are oxygen, heat, and light. Overexposure to heat or UV light will eventually degrade the THC to lower amounts, but don’t worry; showing off your prized bud under some LED lights for a few minutes to your friends here and there won’t do any significant damage.

    It is good to keep your cannabis out of direct sunlight, away from any heat sources, and in a sealed container. If you are someone that thoroughly inspects their cannabis before you smoke – twenty minutes under an LED light will not ruin your stash – make sure that you don’t leave the light on and forget about it.

    Through all of the cannabis reviews and research that I have done, it is apparent that most Cannabis connoisseurs will most likely smoke their stash long before it ever starts to lose its potency unless you leave it in the sun for a week.


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