The endocannabinoid system (ECS) is present in all animals. This system
influences a good number of out physiological behaviors such as energy
intake(hunger), metabolism, mood, and transport of nutrients.
Endocannabinoids are our bodies own form of marijuana and is involved in
most of our bodies cells and structures and help control a number of
functions through out our bodies different systems(nervous, limbic,
immune, ect.). In our nervous system we have
neurotransmitters (dopamine,saratonin) that help send electrical signals
though the body. At some point in time(think invertebrates) the nervous
system acquired a new type of chemical (cannabinoids), these new
chemicals have a very similar structure/shape to
tetrahydrocannabinol (THC). The receptors are not in our bodies because
there is a plant that produces a chemical that makes them react, but
because our bodies produce an chemical that activates those receptors.
It is just coincidence that there is a plant chemical(THC) that acts on
the receptors too. THC binds to the endocannabinoid receptors in the
brain and body, it is this interaction that creates that feeling of being "high".
Smoking
for the first time is different for everyone. Some experience the
feeling of being high and some dont. It is not because they are inhaling
wrong or not smoking enough necessarily. It is because everybody is
different, especially when broken down to the chemical level. The
different chemicals binding to different receptors in your body, and
your body figuring out how to react to these new chemicals as opposed to the ones our bodies naturally produce. Just because you dont feel high your first time smoking doesnt mean that your body isnt reacting to the THC. Of course smoking a lot in a short period of time will get you high you are just overloading your senses, but that is not the only way people get high their first time smoking.
grandpa is not a liar, you are just ignorant.