From the article "Marijuana Health effects"

Marijuana is legal in Washington state. But does that mean it's good for you?"Daily use increases the risk of becoming dependent," says Roger Roffman, a professor emeritus at the University of Washington's School of Social Work. He supported Initiative 502, which called for the legalization of a small amount of marijuana for adults 21 and older in Washington. Roffman says there are positive effects of marijuana use: It can help people relax and interact with others. And consumption for medical purposes can reduce symptoms of disease and treatments of disease, he says. But dependence can cause impairment or distress and other effects that interfere with other areas of life, he says. "It's fairly common for people who are using marijuana regularly to complain that their ability to think clearly is impaired — to remember, to organize their thoughts, to follow through with multitasking." Not everyone who uses marijuana regularly experiences problems with thinking and memory, says Roffman. But researchers have not been able to predict which users will and which won't. "One of the main contributors to worse outcomes (of marijuana use) is the age at which you start," says Baler. "So we are particularly worried about young people who are using the drug." The concern, especially for young people, "is that you're performing suboptimally during those years when you should be working at peak levels of performance," he says. And with day-after-day use, the drug has a cumulative effect on achievement. Studies show that when marijuana is used chronically, "people achieve lower in academics, job performance and life satisfaction," says Baler. "It's difficult to understand why kids working so hard on their education would engage in an act that would lower their chance of success." Marijuana is addictive.  Washington and Colorado became the first states to vote to decriminalize the possession of an ounce or less of marijuana by adults 21 and older. More research is needed on how marijuana affects people of different ages and backgrounds, Roffman says. "There is evidence of genetic vulnerability to dependence. It is still at an early stage of being studied."

• Impaired short-term memory. Marijuana use can make it hard to learn and retain information, particularly complex tasks.
• Slowed reaction time and impaired motor coordination. It can throw off athletic performance, impair driving skills and increase risk of injuries.
• Altered judgment and decision making. Experts say this can contribute to high-risk sexual behaviors that could lead to the spread of sexually transmitted diseases.
• Increased heart rate. It can jump by 20% to 100%, which may increase the risk of heart attack, especially in otherwise vulnerable individuals.
• Altered mood. In some, marijuana can induce euphoria or calmness; in high doses it can cause anxiety and paranoia.
• Addiction.
• Poorer educational outcomes, poorer job performance and diminished life satisfaction.
• Respiratory problems (chronic cough, bronchitis).
• Risk of psychosis in vulnerable individuals.
• Cognitive impairment persisting beyond the time of intoxication.
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