The Stanislaus County Insider

Marijuana use damages brain neurotransmitters.
Dopamine is a naturally occurring hormone and neurotransmitter in our brain that is responsible for feelings of happiness, motivation, joy, pleasure, and an overall sense of well being. It also regulates focus and attention levels. Serotonin is a neurotransmitter that is responsible for mood stability and balance.
Smoking or ingesting marijuana initially causes an increase in the amount of dopamine and serotonin levels in the brain. However, when released in excess repeatedly the brain adapts by reducing the number of dopamine receptors and by doing so, dopamine levels fall dramatically which causes a loss in the ability to feel pleasure, happiness, or motivation.
In a new study by the National Institute on Drug Abuse, researchers recruited 24 marijuana users and 24 non users, with the goal to examine how brains reacted to the drug methylphenidate- a stimulant that increase dopamine levels. The control group produced just as much extra dopamine after taking the drug as the marijuana users. They each produced the same amount of dopamine but with remarkably difference results. Marijuana users had a significantly reduced behavioral, cardiovascular, and brain response to the drug, and reported feeling restless and anxious with heightened stress levels and  irritability. They had a significant decrease in test scores on sensitivity to reward and motivation causing scientists to seriously question whether the brains of marijuana users knew what to do with the extra dopamine. Researchers think the decrease in reward sensitivity may be the cause of depression in marijuana users. Low levels of dopamine and serotonin are a root cause of depression and anxiety. Marijuana smokers will often tell you that using marijuana relieves these symptoms when in fact the drug is actually causing them. Their reaction is evidence that marijuana use damages the brains ability to function properly.
Sidenote: Many people are under the false impression that marijuana addiction is somehow less serious and harmful than other addictions. Not true.  We see a very disturbing and dangerous trend to downplay the harms associated with marijuana use by those with a vested interest in marijuana legalization. 
Groups funded by pro drug advocates are deliberately misleading the public with information that is categorically false. Americanís for Safe Access and the Drug Policy Alliance pay activists to post comments under articles in an attempt to mislead the public. They cower behind screen names and are responsible for conspiring to cover up the truth about the harms associated with marijuana so they can continue to profit off the drug. Marijuana use is linked to brain damage, serious, irreversible mental illness, testicular cancer, heart attacks and strokes, autism and other neurological disorders,  addiction,  a large increase in the number of DUIís,  the tripling of fatal car crashes,  an increase in the number of explosions related to extracting hash oil, an increase in crime, and more. Marijuana is far from a harmless plant.