I've seen a lot of conflicting answers on this, for example I've seen some places cite Myrecene (also present in Mangos & Hops/Beer) as the main terpene responsible for the Indica high. My best understanding is that especially since strains are so cross-bred for their many traits both in growing & medical effect, these days that Sativa/Indica dicotomy is becoming a little blurry, but to only credit the terpenes might be an oversimplification. It definitely plays a role in the effects of the plant, but the hundreds of different cannabinoids likely play an equally important role in the effects. For example THC-v which is most prominent in strains like Girl Scout Cookies or Durban Poison is known to have an energizing effect & actually suppress appetite. These days, Sativa & Indica, outside of growth traits, I think is mostly used to describe effects rather than their origin. Hope this helps!