Editor's note: This article has been reviewed and updated for accuracy in 2026. Mold can settle — sometimes with alarming speed — almost everywhere you look, as well as in even more places where you don’t. To date, scientists have identified over 100,000 different species of mold and mildew. They grow on your walls, on food left out to long, and outside. Some mold species are harmless, while others are even beneficial. Many, of course, pose a threat to human health. With mold being such a ubiquitous phenomenon, it’s only logical that good old cannabis isn’t exempt from its proliferation. Seasoned “canna-oisseurs” might know exactly what to look for, but the fact is that many newer cannabis enthusiasts do not. That matters, because — as you’ll discover in this guide — smoking or otherwise enjoying mold-infested cannabis can have some side effects. Some are mild and a mere nuisance, while others are quite dangerous. The bottom line? You don’t want to dabble in moldy weed. Here’s how you can make sure that your stash is safe, as well as what can happen if you don’t pay close attention and inadvertently inhale or eat moldy cannabis. How to Gauge the Quality of Your Cannabis If you’re after top-quality weed, you need to know what you’re looking for — and that’s true not just when you’re orderi