The amount of Myrcene in a cannabis sample is what dictates the indica or sativa effect. If a sample has over 0.5% Myrcene, it will have indica, or “couch-lock” effects. If a sample has less than 0.5% Myrcene, it will have the soaring Sativa effect. It is simply the amount of Myrcene that is in the sample that dictates how you will be effected.
Next time you get your cannabis tested, get a terpene test on your flower or oil and see if that OG you are running is sativa or indica dominant. This is a fun way of knowing more about your medicine and also a good way to decide if something is gonna be a good nighttime or daytime medicine.
Also reference: ChemSpider