When marijuana is smoked, THC and other chemicals in the plant pass from the lungs into the bloodstream, which rapidly carries them throughout the body to the brain. The person begins to experience effects almost immediately . Many people experience a pleasant euphoria and sense of relaxation. Other common effects, which may vary dramatically among different people, include heightened sensory perception (e.g., brighter colors), laughter, altered perception of time, and increased appetite.

If marijuana is consumed in foods or beverages, these effects are somewhat delayed—usually appearing after 30 minutes to 1 hour—because the drug must first pass through the digestive system. Eating or drinking marijuana delivers significantly less THC into the bloodstream than smoking an equivalent amount of the plant. Because of the delayed effects, people may inadvertently consume more THC than they intend to.

Pleasant experiences with marijuana are by no means universal. Instead of relaxation and euphoria, some people experience anxiety, fear, distrust, or panic. These effects are more common when a person takes too much, the marijuana has an unexpectedly high potency, or the person is inexperienced. People who have taken large doses of marijuana may experience an acute psychosis, which includes hallucinations, delusions, and a loss of the sense of personal identity. These unpleasant but temporary reactions are distinct from longer-lasting psychotic disorders, such as schizophrenia, that may be associated with the use of marijuana in vulnerable individuals. 

Although detectable amounts of THC may remain in the body for days or even weeks after use, the noticeable effects of smoked marijuana generally last from 1 to 3 hours, and those of marijuana consumed in food or drink may last for many hours.

 

The immediate effects of taking marijuana include rapid heart beat, disorientation, lack of physical coordination, often followed by depression or sleepiness. Some users suffer panic attacks or anxiety.

But the problem does not end there. According to scientific studies, the active ingredient in cannabis, THC, remains in the body for weeks or even months.

Marijuana smoke contains 50% to 70% more cancer-causing substances than tobacco smoke. One major research study reported that a single cannabis joint could cause as much damage to the lungs as up to five regular cigarettes smoked one after another. Long-time joint smokers often suffer from bronchitis, an inflammation of the respiratory tract.

The drug can affect more than your physical health. Studies in Australia in 2008 linked years of heavy marijuana use to brain abnormalities. This is backed up by earlier research on the long-term effects of marijuana, which indicate changes in the brain similar to those caused by long-term abuse of other major drugs. And a number of studies have shown a connection between continued marijuana use and psychosis.

 

Marijuana can change the structure of sperm cells, deforming them. Thus even small amounts of marijuana can cause temporary sterility in men. Marijuana use can also disrupt a woman’s menstrual cycle.

Studies show that the mental functions of people who have smoked a lot of marijuana tend to be diminished. The THC in cannabis disrupts nerve cells in the brain, affecting memory.

Cannabis is one of the few drugs that causes abnormal cell division, which leads to severe hereditary defects. A pregnant woman who regularly smokes marijuana or hashish may give birth prematurely to an undersized, underweight baby. Over the last 10 years many children of marijuana users have been born with reduced initiative and lessened abilities to concentrate and pursue life goals. Studies also suggest that prenatal (before birth) use of the drug may result in birth defects, mental abnormalities and increased risk of leukemia (cancer of the bone marrow) in children.