I have posted this link on earlier posts and will post this again as well as pasting certain things that it says. This is from the National Institute of Drug Abuse.
“Marijuana overactivates parts of the brain that contain the highest number of these receptors. This causes the "high" that people feel. Other effects include:
altered senses (for example, seeing brighter colors)
altered sense of time
changes in mood
impaired body movement
difficulty with thinking and problem-solving
hallucinations (when taken in high doses)
delusions (when taken in high doses)
psychosis (when taken in high doses)
Breathing problems. Marijuana smoke irritates the lungs, and people who smoke marijuana frequently can have the same breathing problems as those who smoke tobacco. These problems include daily cough and phlegm, more frequent lung illness, and a higher risk of lung infections. Researchers so far haven't found a higher risk for lung cancer in people who smoke marijuana.8
Increased heart rate. Marijuana raises heart rate for up to 3 hours after smoking. This effect may increase the chance of heart attack. Older people and those with heart problems may be at higher risk.
Problems with child development during and after pregnancy. One study found that about 20% of pregnant women 24-years-old and younger screened positive for marijuana. However, this study also found that women were about twice as likely to screen positive for marijuana use via a drug test than they state in self-reported measures.9 This suggests that self-reported rates of marijuana use in pregnant females is not an accurate measure of marijuana use and may be underreporting their use. Additionally, in one study of dispensaries, nonmedical personnel at marijuana dispensaries were recommending marijuana to pregnant women for nausea, but medical experts warn against it. This concerns medical experts because marijuana use during pregnancy is linked to lower birth weight10 and increased risk of both brain and behavioral problems in babies. If a pregnant woman uses marijuana, the drug may affect certain developing parts of the fetus's brain. Children exposed to marijuana in the womb have an increased risk of problems with attention,11 memory, and problem-solving compared to unexposed children.12 Some research also suggests that moderate amounts of THC are excreted into the breast milk of nursing mothers.13 With regular use, THC can reach amounts in breast milk that could affect the baby's developing brain. More research is needed. Read our Marijuana Research Report for more information about marijuana and pregnancy.
Intense Nausea and Vomiting. Regular, long-term marijuana use can lead to some people to develop Cannabinoid Hyperemesis Syndrome. This causes users to experience regular cycles of severe nausea, vomiting, and dehydration, sometimes requiring emergency medical attention.14
Long-term marijuana use has been linked to mental illness in some people, such as:
worsening symptoms in patients with schizophreniaa severe mental disorder with symptoms such as hallucinations, paranoia, and disorganized thinking
Marijuana use has also been linked to other mental health problems, such as depression, anxiety, and suicidal thoughts among teens. However, study findings have been mixed.
How Does Marijuana Affect a Person's Life?
Compared to those who don't use marijuana, those who frequently use large amounts report the following:
lower life satisfaction
poorer mental health
poorer physical health
more relationship problems
People also report less academic and career success. For example, marijuana use is linked to a higher likelihood of dropping out of school.18 It's also linked to more job absences, accidents, and injuries.19
Marijuana use can lead to the development of a substance use disorder, a medical illness in which the person is unable to stop using even though it's causing health and social problems in their life. Severe substance use disorders are also known as addiction. Research suggests that between 9 and 30 percent of those who use marijuana may develop some degree of marijuana use disorder.25 People who begin using marijuana before age 18 are four to seven times more likely than adults to develop a marijuana use disorder.26
Many people who use marijuana long term and are trying to quit report mild withdrawal symptoms that make quitting difficult. These include: