Does Weed Go Bad? The Science of Cannabis Expiration

does weed go bad

While cannabis doesn’t get better with age like a fine wine, it certainly doesn’t rot like old food. Today let’s answer the question: Does weed go bad? to see if that old cannabis you found is still good to use.

Does Weed Go Bad?

While marijuana is a schedule 1 controlled substance, it’s also a plant. Whether you’re talking about chamomile or cannabis, the moment you pick a plant, it begins to die. That’s because a part of the plant known as their stomata closes.

Stomata are pores (stoma) found on the skin of leaves. They are responsible for bringing in nutrients into the plant. With nutrients cut off, all plants will start to lose moisture. This will cause them to dry out and “go bad”.

What is “Bad” Cannabis?

When you ask: does weed go bad?… it all depends on the perception of the smoker. At the end of the day, the cannabis can lose its flavor and potency. The same goes for other herbs like chamomile.

In fact, old weed can actually change the way it impacts your mind and body. For instance, cannabis shows higher levels of CBN as it ages.

Just like a box of cake mix a few weeks past its expiration date, these dried out plants are not “bad.” They’ve just outlived their “Best by” date. Smoking old cannabis will still give you a small buzz and carry some medicinal properties. However, the smoke might have a bad taste or feel harsh on the lungs.

How to Tell When Your Cannabis Has Gone Bad

In an interview with Canadian news source, Global News, Quebec Brand Manager of Canopy Growth, Adam Greenblatt, explains,

“Dried flower generally has quite a long shelf life, but after about a year, it starts to lose its smell. The THC doesn’t degrade as quickly, but the subjective quality of it starts to degrade.”

Smell is critical when figuring out cannabis has gone past its “best by” date. What causes the scent of marijuana is their terpenes. These aromatic molecules are responsible for both the psychedelic and medicinal properties of marijuana.

does weed go bad how to tell
Once the smell has died down, that means the terpenes are dissipating. Their degradation over time could change the intended effects of the strain. Terpenes and cannabinoids work together, in what is known as the entourage effect, to affect your body and mind. If this careful cocktail of chemicals is altered, even in the slightest, you won’t get the true effects of that particular strain.

If there’s no skunk-like smell when you light up the cannabis, then you can be assured it is past the “best by” date. According to Greenblatt, the best days are “about a year as a rule of thumb.”

Storing Cannabis to Slow Down Expiration

The best way to prolong the life of dried cannabis flower is to store it in an airtight container. This will keep moisture locked in with the cannabis, so it maintains its sticky exterior. Within those resin glands, known as trichomes,  are the terpenes. You want those sticky oils to remain on the flower. That way the resin glands can combust and release the terpenes (and cannabinoids) when you combust the marijuana.

Be sure to read our article on what makes weed sticky.

Storing cannabis in a glass container is the best way to slow down its expiration.

does weed go bad
Does weed go bad? Technically, it can lose it’s potency. But, storing in glass containers, especially darker colored glass can help maintain the original cocktail of cannabinoids and terpenes that give different strains their unique effect profiles.

That’s because glass has no porous surface. Therefore, it doesn’t lock in excess water vapor. Glass also doesn’t alter the flavor of your flower.

Where Not to Store Cannabis

Putting cannabis in a plastic bag will cause your cannabis to dry out quicker. Plastic bags draw in moisture, pulling it out of the flower. Also, plastic is synthetically made. Therefore, the chemicals in plastic may have an adverse chemical reaction with the molecules in the cannabis. In turn, it may compromise some of the cannabinoids and flavor.

Also, don’t put your marijuana in a fridge or a freezer. It will leave cannabis somewhat damp when you take it out to dry. In turn, the cannabis may grow mold.

Dangers of Smoking Old Cannabis

Depending on the conditions where you stored your cannabis for an extended period, the marijuana may grow susceptible to disease. Traces of mold and mildew can fester in marijuana. This is especially true if the cannabis is stored in humid areas, bright rooms, or in plastic bags.

There are many dangers to smoking moldy cannabis. Some side effects include coughing, respiratory issues, and flu-like symptoms.

However, just because your cannabis is old does not mean it will be moldy. According to, you can “age” your cannabis forcing the THC to degrade into CBN. This cannabinoid is helpful when it comes to sleep and pain relief, but can also contribute to “laziness”. So, if you are intending to get energetic effects from a particular strain of cannabis, it’s best to consume it as fresh as possible.

How Long Does Cannabis Oil Last?

While we’ve already let you know the answer to: does weed go bad? (it technically doesn’t), we’ve only been talking so far about marijuana– the buds (i.e. flowers) that emerge from the cannabis plant. Like flowers, concentrate oils also have a “best by” date. However, their shelf life seems to extend even further. While the composition of all concentrates differs, most are comprised of an abundance of THCA.

THCA has a geometric structure made of lattices that stack on top of each other. This shape makes THCA susceptible to other impurities latching on. When THCA is crystallized, these impurities can be locked in. This will inevitably have an impact on how long the concentrate will remain potent.

Fun fact: THCa turns into THC following decarboxylation.

does weed go bad it could impact thca

Over time, nucleation happens in a concentrate. This is when the molecules begin to separate from one another. THCA will remain mostly intact. However, even in concentrates THC will convert to CBN. When this happens, you will notice the concentrate turns from a golden honey color to dark amber. To get the most out of this concentrate, dab at a lower temperature. This will maintain the most cannabinoids and terpenes while bringing out the best flavor.

The purer the concentrate you get, the longer it will maintain optimal flavor and cannabinoids. Just be sure to store the oil much as you would flower. Put it in a dark, cool area. You can probably retain two-thirds of a concentrates potency after two years.

The short answer to the question: does weed go bad? seems to be “no”, unless it is is moldy. The only real side-effects to consuming old weed is lack of potency, an increased likelihood of it being less effective (and making you lazy), and a harsher and less pleasing-to-the-nose smoke.

About Nicco Reggente, PhD 167 Articles
Nicco is the co-founder and CEO of WoahStork and Strain Genie-- two companies dedicated to bringing to life his passion of bringing personalized medicine to the cannabis industry. Nicco received his PhD from UCLA in cognitive neuroscience with a focus on machine learning applied to neuroimaging datasets. He previously received two B.As from NYU in Psychology and Philosophy.

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