Introduction Marijuana is commonly known by other names such as pot, weed, skunk, ganja or grass. Marijuana refers to dried leaves of the cannabis plant that people smoke or eat to get the feeling of euphoria. A substance in the marijuana leaves called delta-9-tetrahydrocannabinol abbreviated as THC causes the euphoria (Steinherz & Vissing, 1997-1998; Monroe, 1998). The abusers of the drug crave for THC, which leads to addiction. Marijuana is among the illegal drugs that are regularly used in the world. In Europe and the United States, marijuana is the leading illegal drug that many people use. Most people smoke it and teens have not been left behind in the craze for marijuana as they start smoking it early. Studies have shown that the effects of marijuana are negative. One of the profound findings of the studies is on the negative effects of marijuana on the brain. The use of marijuana is harmful to an individual and its use should be regulated. Marijuana affects the brain and thus has an overall negative in an individual because it affects the brain, which is a vital organ in the body. It is important to note that marijuana affects other parts of the body such as the lungs but this paper will look at how marijuana affects the brain. Theories of marijuana usage There is a marijuana theory called the stepping stone theory. The theory asserts that the usage of marijuana often leads to abuse of other drugs. Marijuana is said to contain pharmacological properties, which induce the users to try to experiment with other drugs (Mack & Joy, 2001). The theory applies in that if an individual will enjoy the usage of marijuana they are more likely to enjoy stronger drugs than marijuana such as cocaine. The theory presupposes that factors that lead one to start using marijuana are likely to lead to use of hard drugs. Not only does it harm an individual’s brain but also leads to further harm through the introduction to other drugs such as cocaine and heroine (Kring, Johnson, Davison & Neale, 2009). It is important to note that not all users of marijuana end up using other drugs such as cocaine but many users of such drugs as heroine began by using marijuana (Kring et al, 2009). Moreover, people are introduced to marijuana smoking because they are told it has positive effects such as relieving one of stress but the results of the smoking are short lived as when marijuana effects wears off the issues that had caused the stress still remain and he or she must deal with problem to avoid further stress. The other theory is the gateway theory. The theory urges that there is a consistent pattern of drug abuse from adolescence into adulthood. Young people who start the usage of marijuana are more likely to continue the habit in adulthood. The people who are able to gain access to marijuana, which is an illegal drug, also get access to other drugs hence marijuana acts as a gateway to other hard drugs as their access becomes easy (Mack & Joy, 2001). Researches findings on effects of marijuana on the brain Research findings on the brain show that abuse of marijuana for a long time affects the brain just as the other drugs do to the brain. The usage of marijuana affects a person general life. A study sho