Addiction has been listed as a true medical disease. It's not just physical but neurological in nature. The physical part of addiction (withdrawal) can be readily managed with the appropriate medications. The main issue is the uncontrollable, compulsive drug craving, seeking and use. There has been much scientific work that shows a link between the disease of addiction and genetics. As a matter of fact, it is said that if you have an addict in your family lineage, your children have a 1 in 4 chance of becoming an addict themselves if they ever use. Even once. That is all it can take to trigger the limbic system of the brain and begin to rewire the reward system.
The limbic system is located near the brain stem is one of the most basic of brain functions. It links together a number of brain structures that control and regulate our ability to feel pleasure. Feeling pleasure motivates us to repeat behaviors such as eating - actions that are critical to our existence. The limbic system is activated when we perform these activities - and also by drugs of abuse.
The cerebral cortex is divided into areas that control specific functions. Different areas process information from our senses, enabling us to see, feel, hear, and taste. The front part of the cortex, the frontal cortex or forebrain, is the thinking center of the brain; it powers our ability to think, plan, solve problems, and make decisions.
So, just think about what happens when drug use rewires the reward system of the brain and then these reward sensations interact with the cerebral cortex. Once addicted, a vicious loop is wired between the limbic system and the cerebral cortex. This manifests itself in behavior such as obsessing over the drug, how to get it and using. This involves behavior such as lying, isolation and indifference to anyone and anything but the drug of choice.
Many in this thread have basically alluded to their drug use as recreational and they can choose to stop whenever they want. Indeed, that may be the case, but if this disease is truly genetic and even using once "lights the fuse" of addiction, do you really want to take the chance? From someone who has experienced first hand what addiction can do to a person and the family/friends around them, I can honestly say that if you have lived that hell, you would not want to take the chance.