Cannabis Science

Does Weed Expire?

does weed go bad

Most things we use will eventually go bad. When food goes bad it’s usually obvious and if eaten, there are normally negative consequences. Some things like makeup actually have a more inconspicuous expiry date that leads to infections if used past their prime. When it comes to weed, many users wonder if weed goes bad. The short answer is yes, it can. Weed can lose its freshness and potency but it’s not likely to kill you, if you have a normal immune system.

Jump to our visual story on “Does Weed Go Bad?” for a snapshot in under a minute.

How Long Does Weed Last?

How long does it take for weed to go bad? Weed doesn’t technically expire like milk or meats. According to Healthline, it stays fresh for about six months to a year. will stay fresh for that long if it’s stored properly. 

How Long Does it take for Weed to Go Bad?

Since weed doesn’t expire like food, its expiration may not be obvious. Here are some things to look out for, according to Healthline, if the weed is old:

  • Change in smell or no smell at all
  • Sometimes may smell or taste harsh
  • Crumble when you break it off
  • Spongy texture when you break it off
  • Presence of white powdery or fuzzy spots which may indicate fungus
  • Musty/hay smell which may indicate fungus.

Loss of Potency

Another way you can tell if your marijuana is no longer fresh is by the loss of potency. For some people, that may only be lead to annoyance. However, for those using it for medical reasons, it may lead to the treatment not being as effective which of course could lower quality of life. 

According to a study done in 1999, the loss of tetrahydrocannabinol (THC) is proportional to the time stored. The table below shows the amount of THC lost over a period of four years while it was stored at room temperature (20-22 degrees Celsius). 

Percentage of THC lost Time Stored (Years)
Table Showing Percentage of THC Lost from Marijuana Stored Over Various Periods of Time

What Will Happen To Me If I Use Old Weed?

Can weed get old? Unfortunately, yes. The good news is, if you use old weed, there are usually no life-threatening side effects. According to Healthline, if there is mold present on the weed you could experience nausea, vomiting, and coughing. However, if you’re someone with a weakened immune system, using weed that has mold could be deadly. The Healthline article states: “In people with weakened immune systems, inhaling smoke or vapors from weed containing bacteria or fungi could cause serious illness or even death.”

Mold isn’t unique to old weed, mold can even be found on weed you just bought. As stated before, mold on weed tends to appear white and powdery or as fuzzy spots. The smell and taste could also indicate the presence of fungus. For example, weed with mold has a musty or hay smell. Healthline described the taste as “off”.

Inspect weed bought from anywhere for mold. According to researchers, bacteria and mold was found on 20 cannabis samples which were acquired from dispensaries and cannabis growers in Northern California. According to the findings, there was Aspergillus fumigatus, Cryptococcus laurentii and Mucor circinelloides present. Those are the names of fungi that can be pretty invasive in people with weakened immune systems. 

Could Smoke Kill The Fungi?

According to the study most recently mentioned, evidence suggests that smoking marijuana won’t kill the fungi if they are present. The study says that they were able to culture viable organisms even after the sample has been exposed to smoke. The research states, “However viable organisms have been cultured from smoke even after water filtration, suggesting that temporary exposure to elevated temperatures or attempts at filtration are probably insufficient to protect the compromised host.”

Best Way to Keep Weed Fresh

In order to preserve freshness and reduce the growth of mold, care should be taken in how the weed is stored. According to Healthline, light, humidity, temperature, and oxygen can affect cannabis. Here are some things to consider when storing cannabis.

The Type of Container

According to a video from Online Medical Card, it’s best to use clean, airtight glass containers. When storing the marijuana, do not fill the marijuana to the brim of the glass, fill it about ¾  of the way. The video says if you have too little air then the cannabis will dry out but too much air will breed mold. The video also said not to store weed in plastic bags because the potency will decrease and will dry out. In addition to that, Online Medical Card said cannabis should be cured for 4 weeks before storage. 

Healthline backed up a lot of what the video posited. For example, Healthline said that plastic containers and cans were a no no. The article said that plastic containers would affect potency. Healthline said, “Plastic holds static that can affect delicate trichomes — the tiny, crystal-like hairs on flowers that produce cannabinoids and terpenes — and mess with potency.” Glass jars like mason jars, are ideal.


Online Medical Card said to keep cannabis stored between 15-21 degrees Celsius (or 60-70 degrees Fahrenheit) and to keep the cannabis away from heat like leaving it near a microwave. 

Ontario Cannabis Store said that temperature is very important to preserve freshness. The website posits that it is best to keep the cannabis stored below 25 degrees Celsius to prevent the growth of mold.

Even the lower the temperature the better, Healthline says the freezer is not the best place for cannabis. The article said that storing your weed in the freezer could cause breakage of trichomes which are the tiny hairs on flowers that produce cannabinoids. In addition to that, the freezer could expose the weed to moisture and moisture equals mold.


The idea that cannabis should be stored in a cool, dark place is echoed by pretty much every source. 

According to Ontario Cannabis Store, “simply storing cannabis products out of direct sunlight will prevent them from breaking down too quickly.”

Healthline echoed that and added that too much heat could lead to moisture and of course that means mold. They also said, “Aim to store cannabis in a dark place, like a closet or cabinet, with a temperature below 77°F (25°C).”


According to Ontario Cannabis Store, weed should be stored at relative humidity (RH) of 59% to 63%. If the humidity is higher than that the excess moisture could lead to the growth of mold however if it’s much lower than the range stated then the weed could dry out. 

Healthline suggests using humidity packs to your containers or store your weed in a humidor made specifically weed.


While weed won’t go bad like eggs and milk, it can lose its potency and freshness. If you’re someone who is immunocompromised then weed with mold can be life-threatening. If you have a normal immune system you may still feel negative side effects from weed with mold. The best thing to do is to inspect the weed when you receive it and before use to look out for mold. In addition to that, storing the weed using the tips outlined in the article will help to preserve the freshness and the potency as well as inhibit the growth of mold. 


About Trevann

Trevann is Stoner Rotation’s Jamaica-based lead writer for the Science section of our cannabis blog. She graduated with honors receiving her Bachelor of Science degree in Molecular Biology from the University of West Indies, Mona. For the last three years, she has covered some of the biggest questions around cannabis and health underpinned with research from supporting studies, medical journals and scholarly articles. Got something on your mind? You can reach her at [email protected].