While seeing mold on the food we eat, like bread and cheese, is pretty straightforward, it can be difficult to detect on weed. Moldy cannabis can have a greyish or white coloration but this is often how normal cannabis looks; the best way to tell is by the smell, which is unlike the smell of cannabis flowers. and has a mildewy odor that you may have encountered in other places.
Smoking moldy weed isn’t dangerous (in the sense that it could lead to significant health impacts) but can result in nausea, coughing and vomiting which, while not fatal, are certainly unpleasant. If you are allergic to mold it can cause inflammation of your lungs or sinuses and can lead to sinus pain, drainage of the sinuses, a feeling of chest congestion and wheezing when you breathe. People that have compromised immune systems or lung conditions, however, can suffer serious health consequences.