Edible based cannabis have significantly different effects when compared to inhalable or smoking based cannabis products. This is primary due to the way it is metabolized. When you smoke cannabis flower or distillate based vape cartridges THC gets absorbed through the lungs instantly and the effects present themselves in minutes, while peaking at around 10 to 30 minutes, and lasting for around 2 hours. Edibles get processed by cytochrome P450 enzymes in the liver that hydroxylate the delta-9 THC to form 11-hydroxytetrahdrocannabinoil (11-OH-THC). 11-hydroxy-THC is said to be around 5 times as potent as delta-9-THC and is able to pass the blood-brain barrier easier. However, the effects typically delayed a few hours and could last around 24 hours, with the exact time varying for each person due to differences in metabolism cause by a genetic predisposition to produce more or less of the cyp450 enzymes.
Since it can take around 3 hours for the effects to peak, it is often difficult for people to modulate dosing correctly and titrate to an optimal dosage. Negative effects of cannabis are often had by new users ingesting a specific amount, not feeling the effects after hour, and then re-dosing, leading to amount where you’re not going to have a good time (source). Negative effects can also result from non-reputable producers not having a batch to batch consistency, lack of homogeneity in the product (ie will you receive the same dose if you cut the product into ¼ pieces), or lack of adequate lab testing consisting of LC-MS/MS with isotope labeled internal standards that match the sample matrix to give accurate results.
A study headed by Ryan Vandrey, PhD at John Hopkins University along with others has suggested that edibles in California and Washington had a large amount of incorrectly labeled products. Only 17 percent of the products were accurately labeled with respect to THC concentration, while 23% had more THC than advertised, and 60% had less. Some edibles even contained up to 50 more THC than labeled, placing patients at risk of experiences adverse effects. However, this research used HPLC as their method for determining THC content whereas, much more accurate methods including tandem mass spectrometry (LC-MS/MS) have been developed. Such techniques have lower limits of detection and can unequivocally quantify THC based on its retention time and mass to charge ratio.