If you're a medical marijuana patient or recreational smoker, you may have come across a nug that's past its prime.

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A handful of states require medical marijuana dispensary packaging to bear expiration dates, according to Leafly's database of state-by-state packaging laws. However, in most areas, smokers are left to their own devices when it comes to determining if a plant is old to smoke.

Here's how to tell if your pot is past its prime.

1. You get sleepier when you smoke it.

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"Basically, three things happen as cannabis material ages," Nolan Kane, a plant geneticist at the University of Colorado told ATTN:. The first of those three is that smokers will find themselves getting drowsier than usual after ingesting it.

This is because some of the major components of cannabis degrade over time. Cannabis plants contain more than 480 natural compounds, 66 of which are cannabinoids. These chemicals target receptors throughout the human brain and body and comprise what is known as the endogenous cannabinoid system, as NORML explains.

Tetrahydrocannabinol, or THC, is likely the most well-known cannabinoid due to its psychoactive properties, though THC also has numerous medical uses for pain relief, insomnia, and other ailments.

"THC degrades into cannabinol (CBN), resulting in lower potency, as CBN does not have strong psychoactive effects," he explained. "Also, CBN may make users sleepy."

2. Expired marijuana loses its smell.

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The second part of the aging process involves terpenoids, which are oxidized oil compounds associated with how strains smell. "Terpenoids will also evaporate and degrade," Kane said. "These compounds cause the smell and taste of particular strains, and may also alter the effects of THC, though this is less well studied."

Expired marijuana won't necessarily smell bad, it just won't smell like much of anything at all, explained Michael Backes, author of "Cannabis Pharmacy: The Practical Guide to Medical Marijuana," in a 2015 Quora post.

3. It will look different, too.

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The third sign of an old bud involves tangible changes to the plant. "The plant material itself will start to degrade, usually drying out, but if it's too wet it could also rot, depending on storage," Kane said.

Washington state marijuana advocacy group VIMEA explains how to identify mold on marijuana plants in a YouTube video.

The bottom line is that weed, like other plants and living things, eventually degrades even in ideal storage conditions.

The best way slow the aging process is to store marijuana in an airtight sealed jar in the dark, as High Times reports, but Kane cautions that changes can occur nonetheless.

"All three of these will happen more slowly under proper storage, but degradation will happen to any plant material even if well-stored," Kane said.