Dear Herb: I found my missing cannabis! Has it lost potency, and is it safe to use?

Not all hash that wanders is lost


Advertise with us

Dear Herb: A friend gifted me some hash approximately six months ago, and it went missing.

Read this article for free:


Already have an account? Log in here »

To continue reading, please subscribe with this special offer:

All-Access Digital Subscription

$4.75 per week*

  • Enjoy unlimited reading on
  • Read the E-Edition, our digital replica newspaper
  • Access News Break, our award-winning app
  • Play interactive puzzles

*Pay $19.00 every four weeks. GST will be added to each payment. Subscription can be cancelled anytime.

Hey there, time traveller!
This article was published 14/08/2019 (1268 days ago), so information in it may no longer be current.

Dear Herb: A friend gifted me some hash approximately six months ago, and it went missing.

I was recently cleaning out my things after a camping trip and found the hash at the bottom of my backpack. Is it still safe to consume? Will it have lost its potency? — Forgetful Stoner, St. Boniface

Dear Oublieux: Thanks for writing in, and congratulations on your reunion with your long-lost cannabis concentrate. Let’s begin with the issue of potency.

Herb answers your questions about legal consumption and growing, the law, etiquette — you name it, he'll look into it.

We know that THC degrades over time into a less-psychoactive cannabinoid called cannabinol (CBN), causing cannabis to lose its psychoactive potential. The exact rate of degradation depends on a variety of factors, including ambient temperature and humidity, oxygen exposure, and light or darkness.

The earliest published research I can find on the topic dates to 1969, when a researcher with the U.S. Customs Laboratory tested three different “marihuana” samples that were kept at room temperature for a month, as well as a sample of Colombian cannabis that had been sitting at room temperature for more than five years. She determined that the THC in her samples degraded at a monthly rate of between three and five per cent. Later research reports lower rates of THC degradation in cannabis samples stored in glass jars, with a 1973 study reporting annual degradation rates ranging from 3.8 per cent when stored in a freezer to 6.9 per cent when stored at room temperature. Either way, scientists agree: THC doesn’t last forever.

Contemporary research has tested how different forms of cannabis degrade under different conditions, and a group of Italian scientists published a paper on the topic earlier this year. The researchers took six different cannabis samples — three bud samples and three hashish samples — and stored them under a variety of different conditions for four years. They tested the samples every 100 days.

As they expected, the Italian researchers found that the THC in both the cannabis bud and the concentrated hash degraded over time. In the samples stored at room temperature, the researchers wrote, “almost 100% of THC was degraded after four years.” Samples kept at a cooler temperature degraded more slowly. (That doesn’t necessarily mean it’s a great idea to freeze your cannabis, as I discussed in this previous Dear Herb.)

I don’t know exactly how your hash was stored in your backpack, and it’s impossible for me to say exactly how much THC you lost while your hash sat forgotten, but its safe to say that it’s less potent than it was six months ago. If the hash was sealed in a container of some kind, it almost certainly fared better during its half-year staycation.

Is it still safe to consume your forgotten hash? I think the biggest risk here would be fungus. You’d be wise to inspect your hashish with a magnifying glass or a loupe, and check it out under a blacklight if you have one. If you can see any mould growing, or if the hash smells like mildew, I would recommend avoiding consumption — inhaling mould spores could be dangerous, especially for people with a compromised immune system.

If you can’t see any suspicious fungus but you’re still worried about mould, you could also try sterilizing the hash. A 1991 letter by two physicians, published in the journal Annals of Internal Medicine, states that some common Aspergillus fungus spores found in cannabis can be killed off, without degrading the THC, by baking the cannabis in an oven at 150°C for 15 minutes. (They tested this method on Aspergillus-inoculated oregano, parsley and tea, so I’m not sure it would work on hash.)

If the hash was exposed to moisture during its time in your backpack, or if you have a compromised immune system, just toss it. To mix clichéd proverbs, you’re better safe than sorry and there’s no use crying over spilled hash.

Got a question about cannabis? Herb answers your questions about legal consumption and growing, the law, etiquette — you name it, he’ll look into it.

First, please check this list of questions already answered by Herb. Then, email, or to submit anonymously, fill out the form below. Please include an email address if you’d like to be notified when Herb answers your question:  


Report Error Submit a Tip


Advertise With Us