Expiration date: Can cannabis go bad?

On an episode of the PBS program “Antiques Roadshow” that aired in early April, the owner of a 100-year-old medicine cabinet received both good and bad news.

The good news? The cabinet, which contained 288 compartments designed to house herbs and/or roots that served as medicinal remedies, was deemed to be worth between $5,000 and $7,000.

And the bad? The contents of three of the compartments were missing, including the one labeled “cannabis sativa.” Turns out the brother of the cabinet’s owner had found the stuff and already smoked it.

News reports of the incident failed to say whether the brother ended up getting high.

But the story poses a good question: How long does cannabis retain its potency? And as with most everything else involving cannabis, the answer depends on a number of factors.

Let’s begin by referring specifically to actual marijuana leaves. As writer Miles Klee wrote the online magazine Mic.com, “The fact is, no matter what some bro on a message board told you, weed is never going to expire or rot quite the way milk and meat do. It’s also not going to get significantly less potent or age like a fine wine if you hold onto it for a year.”

“Even so,” Klee added, “you might say that weed has something of an unspoken ‘best used by’ date.”

Leaves can dry out over time. What is most detrimental to cannabis leaves, however, is moisture, which can cause the growth of mold. So what is really important is to know how best to store your stash.

In a blog post last updated in February 2020, Namaste, a premium cannabis brand from the Canadian producer Zenabis, names four factors that affect cannabis’ freshness: humidity, light, temperature and air.

Humidity can cause mold, a problem that can lead not only to a bad taste but also to health issues such as headaches, vomiting and diarrhea. Light can break down cannabinoids, as can high temperatures (whereas cold can, again, lead to the growth of mold). And air can both affect taste and reduce potency.

The blog post lists various ways to “keep weed fresh,” but it really comes down to making sure your product is fully cured, stored in an air-tight glass (not plastic) container, and kept in a cool, dark place.

High Times, the magazine that calls itself “the definitive resource for all things cannabis,” echoes much of the above advice. As expected, though, the tips writer Nick Lindsey shared are even more, uh, “definitive.”

As for how long weed will be potent, Lindsey wrote, “If it’s been properly harvested, dried, cured and then stored, you can expect your weed to stay fresh anywhere from six months to a year.”

Yet since most people don’t, or can’t, replicate ideal conditions – especially involving light and temperature – Lindsey advises consuming your stash within that first six months.

Here are the specifics of that potency loss, according to the United Nations Office on Drugs and Crime: Weed loses “roughly” 16 percent of its THC after one year, 26 percent after two years, 34 percent after three years, and 41 percent after four years.

So, clearly, the sooner you consume your weed, the better.

But, then what about other cannabis products? No longer limited to flower for homemade joints, bongs or brownies, the legal cannabis market has multiplied the ways cannabis can be consumed – edibles in all flavors, tinctures and topicals, wax with a dab rig. And all of it must be packaged with precision by meticulous processors under the watchful eye of the Washington State Liquor Control Board (edible processors are additionally regulated by the Department of Agriculture).

For edibles, High Times advises, keep them in their original packaging and, as with weed, store them in an enclosed space, away from light and high temperatures. The same holds for concentrates – oils, tinctures, resins, etc. – with the proviso that you place them in “small containers designed specifically for dabs.”

And vape pens? No need to worry about humidity or exposure to air, since the pens themselves are airtight. But direct sunlight can be a problem. In addition, Lindsey wrote, consider standing your vape pen upright “as this will keep all the oil at the bottom of the cartridge, ready for immediate use.”

That, then, is your basic guide to protecting the potency of your cannabis. Here, though, is a final bit of advice, which is just common sense:

Whatever method you choose to store your stash, keep its location a secret from your brother.