Happy 4/20! Here's what happens to your body and brain when you smoke marijuana

It's April 20. For those not in the know, "4/20" is the unofficial holiday that pot smokers and marijuana legalization activists around the world celebrate by lighting up.

The plant, best-known for its "feel-good" effects and touted for its uses for multiple diseases, can also damage our bodies and minds.

The high you get from marijuana mostly comes from a chemical called Tetrahydrocannabinol, also known as THC, which is found in varying amounts in different strains of cannabis.

Another important compound is cannabidiol, CBD, which is thought to cause many of the medical effects of marijuana. There are also more than 70 other chemicals in marijuana that could also cause effects on the brain and body that haven't been well studied.

Most of THC's effects happen in the brain, where the chemicals in the plant interact with receptors on brain cells called cannabinoid receptors. Our bodies actually make chemicals very similar to THC, which are used in normal brain function and development. THC co-opts these natural pathways to produce most of its effects, which are varied and depend on how much and how often someone uses pot.