Drugs: Causes and Effects of Smoking Marijuana

Causes
Marijuana is not a physically addictive substance.  The user’s body does not become dependent on the drug in any way however, this does not in any way detract from its addictiveness. 
Marijuana addiction is characterized as emotional and psychological.  This is because inhalation of marijuana puts the user in a euphoric state.  After regular use of the substance, the user’s mind starts to think that it is because of marijuana that they are feeling happy.  This addict mentality increases the frequency the user takes the drug.  The drug induced state of euphoria conditions their brain to adjust to the high level of ‘happiness’ by raising the threshold for happiness by closing down dopamine receptors that regulate happiness and motivation.  This subjects the addict to frequent periods of depression.

Effects
Like most frequently abused substances, marijuana has many adverse effects on the user.  It kills off large amounts of brain cells so after chronic use, this drug will put the person in a soporific state. 
THC in marijuana can rapidly pass from the lungs into the bloodstream which will carry this chemical substance throughout the body.  THC can connect to cannabinoid receptors on nerve cells.  These receptors are found in parts of the brain that control pleasure, memory, thought, concentration, perception and coordinated movements so over time, an addicts ability to perform these processes will gradually decline.
Long term use of marijuana may lead to cancer in the lungs or other parts of the respiratory tract because marijuana smoke contains irritants and carcinogens. 
Short term effects of marijuana can include problems with memory, distorted perception, loss of coordination and increased heart rate.  A study by Dr. M. Maclure showed that a user has quadrupled the chance of suffering from a heart attack one hour after smoking because marijuana’s effect on blood pressure, heart rate and reduced oxygen capacity of the blood.