Let’s say you chance upon a stash of weed you forgot about some time back. Happy day! But … is it even good? You don’t even remember stowing it away, let alone when you bought it. Can you still smoke it?

Can Weed Go Bad?

The good news is, weed doesn’t really “go bad;” its chemical makeup just changes. Marijuana is a plant, just like the veggies and herbs in your kitchen. Cells break down, molecules oxidize. Just as the dried oregano in your spice rack becomes less flavorful over time, weed becomes less potent. Old weed won’t kill you, but it also won’t get you all that high.

How to Store Weed

The best way to avoid this question in the first place is to store your weed properly. Glass or ceramic containers are your best bet. You want to make sure the container is airtight, and won’t transfer smells or flavors onto your precious weed. Store your pot in a dark, cool refuge that’s not your refrigerator or freezer — too cold environments can suck the sweet, sweet moisture out of those leaves. Fresh weed is full of the cannabinoids CBD, CBC, and THC, but sit your weed down for a bit in ultraviolet light (i.e., sunlight), and your THC will break down into CBN, a cannabinoid that is way less potent and much more disappointing. Basically: Keep your weed in a still, dark, cool environment, and you’re guaranteed the best flavor.

weed in glass jar
A container with an airtight lid means the freshest weed possible.

But let’s say you didn’t get around to storing your weed like you should have, and now you’re stuck with a Ziploc bag of mystery marijuana that may or may not be good.

Appearance

If your recently discovered stash doesn’t look much like weed anymore, just some dried out powdery leaves, it’s probably not going to be all that enjoyable to smoke. If you spot a fuzzy white powder growing on it, your weed is moldy and you definitely shouldn’t smoke it, unless you want to risk heart and lung problems. Mold spores, like moist places without a lot of airflow, which can happen if you store your weed where it’s too moist.

Sound

When you pull apart your re-discovered weed in your hands, you should hear snaps, not crackles, which can mean your weed is too dry. If your weed is silent, it has a lot of moisture, and you should be on the lookout for mold.

Smell

If your old stash smells musty, or like urine or a locker room, mold is probably the culprit. Chemical or plastic scents are a result of poor storage or pesticide contamination. Old weed might not smell as strong as the day you stuck it somewhere and forgot about it, but it shouldn’t have any off smells. Weed should smell like weed.

Taste

If it looks like your old stash is free of mold, and you decide to light some up, you’ll know pretty quickly if it’s really gone bad just by the taste. It should still taste like weed, without off flavors.

Smoking poor quality weed won’t hurt you (with the exception of mold) — it just won’t be quite as enjoyable as the fresh stuff. You probably won’t get as high thanks to a lower THC content, but that’s about it. Enjoy your re-discovered stash!

Photos via Dank Depot on Flickr, Getty Images / Justin Sullivan

Kelsey Kennedy is a science journalist from Oregon, now based in New York City. She's written about science, technology, and the environment for Quartz, Undark, and Scienceline.