Despite the fact that marijuana is legal in the state of Washington, underage use of the drug can cause permanent damage in the developing brain. Research indicates that teenage marijuana users process memory, emotions, and sleep patterns.

In a word, yes. Like with any other drug, excessive marijuana use can result in dependence, where you feel negative consequences from not taking a drug. People who are dependent on marijuana often report sleep problems, irritability, and changes in mood and appetite when they stop.

It would be very difficult—some say impossible—for you to inhale or ingest a fatal amount of marijuana. However, that doesn't mean you can't overdose. With the increasing prevalence of edibles and the development of ever-stronger strains, marijuana overdose is actually on the rise. People who overdose on marijuana experience extreme anxiety, panic, and disorientation that can result in hospitalization. 

Because salvia also comes from a plant, it is often inaccurately compared to marijuana. However, unlike marijuana, salvia is a hallucinogenic drug that can cause feelings of altered reality, loss of body control, extreme anxiety, and fear. The medical side effects are not fully known, but it is thought to have an effect on the brain, gastrointestinal system, and heart.