There are over a hunderd different types of cannabinoids.

They all have different effects on the unique brain chemisty of an individual but also influence the effects of eachother. (Entourage effect)

There are an uncountable amount of combinations here with an uncountable amount of specific effects.

It has to be said that all drugs carry real risks and cannabis is not harmless.

But with the info above i have always believed in its potential to one day synthesize fully personalized medicine. Other then many other drugs endocannabinoids are also created naturally in the mamal brain and are very important for mood regulation and cognitive function.

An interesting fact is while people would shudder by the idea of giving these substances to infants, breastmilk is actually a huge source of natural cannabinoids.

Others are answering about some of the science.

I want to point out that marijuana was a schedule I controlled substance in the United States for many decades, with no accepted medical use. During that time, it was exceedingly difficult to do research with cannabis, and licenses were very strictly controlled by the DEA. As a result, a lot of the research we want to have has simply not been there.

The situation is starting to turn around now, but it takes a long time to turn the ship around.

Everybody's brain is a little bit different and reactive differently to "substances". Cocaine, for instance, does nothing to me that I can describe as high though it will numb my gums if I rub on them.

There's also lots of different cultivars of weed, with varying amounts of certain compounds(cannabinoids), causing different expected effects. So, one kind might put me in the mood to tear an engine down while the one in the other bag makes me want to play rogue-likes on my phone, on the couch, with a bag of Doritos.

Dunno about the science, but for me the sensations caused by different strains lead to different behaviors.

"Body high": Muscles feel loose and relaxed, maybe a floaty sensation. I could get up and do something productive, but it's just so cozy right here. Then I veg out and eat.

"Head high": My mind is drawing a lot of connections between things, not quite racing thoughts, but a lot of analysis and half-finished ideas. I see a dirty plate and think "Better take this to the kitchen" then on the way there I see some dirt on the floor so I set the plate down and grab a broom. Then I realize how inconvenient it is that the broom closet is so far from the kitchen, and now suddenly I am reorganizing the house.

Doesn't even do anything for me. I've tried it on numerous occasions and not once gotten "high". I can't even tell you what high is other than from observing others. Eventually stopped cause I was just wasting my money.