The primary active chemical which makes cannabis a drug is tetrahydrocannabinol, more commonly known as THC. It is a psychoactive chemical substance, meaning that it has effects which influence the mind and the consciousness of the individual. When an individual smokes marijuana or consumes the drug in some other manner, THC travels through the bloodstream to the brain, and this is where it achieves its primary intoxicating effects in getting the person high. The result in most cases is that the marijuana user ends up feeling sensations of euphoria. This experience is attributable to the fact that THC works on areas of the brain which are associated with feelings of pleasure and with rewards. Specifically, the drug works by causing the brain to release the neurotransmitter dopamine, the brain chemical that is linked with elation, euphoria and other desirable sensations.

Following euphoria, a person using marijuana will typically experience relaxation, often to the point of being nearly incapacitated. He or she may notice distortions of sensory perceptions, and might feel giddy or experience a state of glee. As the drug wears off, the person is liable to fall into a depression or might even start feeling paranoia or panic. This might even proceed into an acute psychosis, during which the person may hallucinate or suffer from delusions.

Marijuana’s Effects On The Brain

Beyond the experience of the high, marijuana has other effects on the brain. For example, the drug interferes with the ability to form new memories. This has to do with the fact that the hippocampus, the area of the brain which is thought to be responsible for the formation of new memories, has a high concentration of cannabinoid receptors, brain cells to which THC binds. Studies have demonstrated that continued exposure to cannabis causes major cell loss in the hippocampus, thereby reducing memory potential.

Marijuana consumption also makes it difficult for the person to shift his or her focus from one thing to another; the individual’s attention will often become fixed on one thing. In addition, THC binds itself to certain parts of the brain that have to do with coordination, reaction time and balance, with the result that the individual may become physically inept and will very often be unsafe to drive an automobile. Some of these effects are temporary and will wear off as the person comes off of the high, but others may be more lasting or even permanent. Tests including MRIs have demonstrated that chronic marijuana users will experience certain changes in brain structure.

Physiological Effects of Marijuana

While the brain may be the primary part of the body which allows marijuana to produce its high, it is not the only part of the body which is affected by cannabis consumption. Smoking marijuana causes a rapid increase in the user’s heart rate, often by as much as 50 beats per minute.

Along with the boost in cardiovascular activity, the blood vessels in the user’s eyes will expand and the eyes will often look red as a result of the increased blood supply. The bronchial tubes will also relax and expand, increasing the supply of oxygen to the lungs. On a long-term basis, marijuana users often develop bronchitis, a condition of having a chronic cough. This is primarily found in those who smoke cannabis, because the particles found in the smoke can irritate the lungs. Research has demonstrated that, for this reason and others, marijuana users are statistically more likely to miss time at work.

Marijuana smoke also contains substances which are known to cause cancer. In fact, pot smoke has as much as 70 percent higher concentrations of carcinogens than cigarette smoke, though the risk of cancer may not be as great since marijuana users are not smoking as much or as often than those who smoke tobacco. On the other hand, pot smokers typically inhale far more deeply and hold the smoke in their lungs for longer periods of time. Cannabis advocates often argue that their favorite drug is not as dangerous as others, but the fact is that marijuana is not safe to use. It has harmful effects on the body, in addition to the mental and emotional consequences of getting high.

Source: http://www.drugabuse.gov/publications/marijuana-abuse/how-does-marijuana-use-affect-your-brain-body