When THC is formed in cannabis, it is in the non-psychoactive form, THCA. The “A” represents carboxylic acid (COO-) that is attached to the compound. This small difference changes the properties of the two compounds, which is why simply eating cannabis won’t get you high. It must be decarboxylated first, from THCA into THC, to obtain the psychoactive effect.
To decarboxylate, THCA must be heated beyond 125-135 °C (257-275 °F), like when you are smoking flower. When smoking a joint or a bowl, the flame from the lighter combusts THCA and releases THC and CO2 in a gaseous form that can be absorbed into your bloodstream through your lungs. The amount of heat and time needed to fully decarb THCA will vary depending on numerous variables, including the amount of flower, its moisture content, type/size of oven, heating vessel, etc.
When making edibles, the oven lets us heat the flower at an exact temperature and time allowing for a more controlled and complete conversion. Once the flower is fully converted to THC, it can be used to make various infused products that can be absorbed into the bloodstream numerous ways, such as through the skin or digestive tract.