"How long does the effectiveness of marijuana last while in bud form? What about other forms – do oils and tinctures last longer than bud? "
I think this has happened to everyone, where they find marijuana stashed away somewhere. 18 months is a fairly long time though! The good news is, if it was not exposed to sunlight or water and was kept in a reasonably cool and dark place it will most likely be OK. That said, the cannabinoid profile may have changed slightly.
According to Colorado Pot Guide:
"As cannabis grows, it produces a substance called cannabigerolid acid (CBGA) which is then synthesized into one of three major cannabinoids: CBDA, CBCA or THCA. Through a process called decarboxylation (heating the product), these cannabinoids are transformed into CBD, CBC and, of course THC. Cannabinoid potency largely depends on the strain profile and harvest/curing methods."
If exposed to heat or sunlight, THCA might convert to the cannabinoid, CBNA, which will be converted to CBN once heated. CBN is not as psychoactive as THC which is the psychoactive component of marijuana.
Harborside Health Center, one of the largest and most prominent dispensaries in California states the following rules when storing your marijuana:
• Rule # 1: heat will dry it out and too much moisture can cause dangerous bacteria to grow, • Rule # 2: light is harmful to the trichomes (the sticky resin glands attached) , • Rule # 3: air will dry it out and lessen its potency • Rule # 4: too much handling causes the trichomes to come off.
To store cannabis properly you should invest in an airtight container, like a mason jar, and store it in a cool, dark closet. Ideally you should air the container once a month if you keep it for 6 months or longer. You can also add moisture with a Humidipak placed in the container as well. Some people store their marijuana in the freezer although this is said to destroy the trichomes which are an important part of the equation when you need medicinal cannabis. It is not recommended to do this.
Cigarrets that are stored at 0-(-18) C in a dark, tightly closed container are stable for months. When stoked at +18C 1/3 THC lost over 5 years, while some increase in CBN. When stoked in a room temperature, alteration in color and arome are detected within 9 months; and conversion of THCA to THC is detected as early as at 1.5 month and increase to 25% at 18 months. The ideal storage of cannabis is 2-6 *C for 12 months.