Does Weed Expire? Shelf Life, Storage and Mould
Does weed expire? Not the way food does. Dried cannabis doesn’t go off on a set date, but it slowly loses THC, aroma and flavour, and if it’s stored damp it can grow mould. Stored well, flower keeps most of its THC for a year or more, though its smell fades within months.
The Baller Club Briefing: does weed expire? 0:29
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Filmed in November 2026. Dates and prices in the video are from the day we filmed. The site always shows the current ones.
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Top story today: does weed expire? Not the way food does.
A study published by the United Nations found flower at room temperature lost about 17% of its THC in a year.
Old flower gets harsher and smells like hay. Fuzzy grey spots are mould, and that bud goes in the trash.
Keep it in an airtight glass jar, cool and dark, at 55 to 62% humidity. And don't freeze it, unless you want trichome confetti.
The full story's on our blog. Keep it sealed.
How long does weed last?
THC breaks down over time, mostly from heat, light and air. A study published by the United Nations Office on Drugs and Crime measured cannabis stored at room temperature for four years and found it lost about 17% of its THC after one year, and more each year after that (Ross and ElSohly, 1997).
| Time stored | THC lost | CBN to THC ratio |
|---|---|---|
| 1 year | about 17% | 2.5% |
| 2 years | about 27% | 6.7% |
| 3 years | about 35% | 9.4% |
| 4 years | about 41% | 14.2% |
The UNODC samples sat in closed barrels in a dark, air-conditioned vault at 20 to 22 °C. Most of the loss came in the first year, and after two years it slowed to about 7% a year.
The THC figures are averages across several varieties, and single samples were typically about 7 percentage points above or below them.
As THC breaks down, some of it turns into CBN, a different cannabinoid. That’s why old flower tests lower in THC. Freshly dried flower has no CBN, so labs use the ratio of CBN to THC to estimate how old a sample is.
In the UNODC samples, the CBN to THC ratio rose from 2.5% after one year to 14.2% after four. Not all of the lost THC had turned into CBN.
Aroma fades faster than potency. Terpenes, the compounds behind the smell and taste, evaporate over time, so old flower often smells flat or like hay.
In a 1996 University of Mississippi study, dried buds kept in a paper bag at room temperature lost about a third of their remaining aromatic oil in three months. Myrcene, the main terpene in those buds, dropped the most.
How long each type keeps
The storage studies we found cover dried flower and hash, so some rows are thinner than others. Where we found no test, the table says so.
| Product | What the research shows | How to store it |
|---|---|---|
| Flower | About 17% of the THC gone after a year and 41% after four, in closed barrels in the dark | Airtight glass jar, dark and cool, 55% to 62% humidity |
| Pre-rolls | The same flower, ground. Air did less damage when the resin glands stayed whole, so whole buds keep better | In their tube, dark and cool; use the oldest first |
| Extracts | In 1976 tests, hash and extracts kept dark at room temperature were reasonably stable for 1 to 2 years. Hash kept in a freezer showed no THC loss after 4 years | Sealed, dark and cool |
| Vape carts | We found no shelf-life tests. A cart hardware maker says heat thins the oil so it can run into other parts of the cart, and cold thickens it | At room temperature, out of hot cars and pockets |
| Edibles | Little published testing. A 2026 review lists edibles among the products that still need stability studies | Sealed in the package, cool and dry; go by any date on the pack |
Sources: the UNODC study above, a 1976 storage study, a 2026 review of cannabis stability and a cart hardware maker’s care notes.
Signs your weed is past its best
There’s no fixed date when flower goes off, so judge it by these four checks.
- Smell: faint, musty or like hay instead of the strain’s usual aroma.
- Feel: so dry it turns to dust when you break it up.
- Taste: harsh and flat when smoked.
- Look: dull and faded.
Old, dry weed is weaker and harsher, but it hasn’t spoiled.
How to tell if weed is moldy
Mould is the one sign that means weed has gone bad. Look for:
- white, grey or fuzzy spots that look like cobwebs or powder
- a musty, damp or mildew smell, a bit like a wet basement
- buds that feel damp or spongy
Trichomes, the tiny crystals on good flower, can look similar. They sparkle and look like tiny mushrooms under a magnifier. Mould looks fuzzy and flat.
For more on what the crystals are and what frost says about quality, see trichomes.
Don’t smoke, vape or cook with mouldy weed, and don’t try to save part of a mouldy bud. Throw it out.
If something in an order looks off when it arrives, the FAQ explains how to make a claim. A video of you opening the package helps.
How to store weed so it lasts
- Use an airtight glass jar. Glass doesn’t add smells, and an airtight lid keeps air out. Plastic bags let in air and crush buds.
- Keep it dark. Light breaks down THC. A cupboard or drawer works. In a 1976 storage study, light was the biggest single cause of cannabinoid loss, even without direct sun.
- Keep it cool. Room temperature or a bit cooler is fine. Avoid the top of the fridge, a sunny windowsill or a hot car. Older tests cited in the UNODC paper found THC almost entirely gone from cannabis kept at 37 °C.
- Control humidity. Around 55% to 62% humidity keeps flower from drying out without growing mould. A two-way humidity pack in the jar does this for you. Every order with flower from us ships with a humidity pack, including Mix & Match flower packs and regular pre-rolls.
- Don’t freeze flower. Freezing can damage trichomes, which leaves the THC inside them more exposed to air.
- Leave some space. Fill the jar most of the way, but don’t pack the buds down.
- Date the jar. Write the date on a label or a strip of tape when you fill it, so you use the oldest flower first.
The drying and curing guide covers the jar method in more detail.
What about edibles, oils and vapes?
Edibles, oils and vape carts age differently from flower, and many have a best-before date on the package. See do THC gummies expire? and does CBD oil expire? for those.
Common questions
How long does weed stay good for?
Stored airtight, cool and dark, flower keeps most of its THC for a year or two. A 1976 storage study called it reasonably stable for that long, and the UNODC samples had lost about 17% after one year. The smell fades sooner, within a few months.
Is it okay to use expired weed?
Age alone lowers quality, so expired flower is weaker, harsher and flatter in smell. Throw out any weed with mould on it.
Will expired weed still work?
Expired weed still has most of its THC, though less than when it was fresh. In a UNODC study, flower stored at room temperature had lost about 17% of its THC after one year and about 41% after four. Some of the lost THC turns into CBN, a different cannabinoid.
Is 2-year-old weed still good?
If it was stored airtight, cool and dark and shows no mould, expect it to be noticeably weaker and harsher. Flower in the UNODC study had lost about 27% of its THC after two years. If it was stored badly, check carefully for mould first.
Can you smoke weed that’s been left out?
If it was left out briefly and isn’t damp or mouldy, yes. It just dries out faster. Put it back in an airtight jar.
Can you cook mould out of weed?
No. Throw mouldy cannabis out rather than trying to cook, bake or smoke it.
