Alan I. Leshner, Ph.D.
National Institute on Drug Abuse
National Institutes of Health
Department of Health and Human Services
June 16, 1998
Statement for the Record
Thank you for inviting me to participate in this hearing. What I would like to do this morning is illustrate through the use of some recent research findings what science has come to teach us about one of our Nation's most serious public health problems--drug abuse and addiction. I would like to point out at the onset that the scientific advancements in the drug abuse and addiction field have been coming at an extraordinary rate and are truly revolutionizing how we, both as a field of science, and as a society, approach the complex problem of addiction.
We have learned a great deal about what drugs do to the brain in recent years. In fact, we now know more about abused drugs and the brain than is known about almost any other aspect of brain function. By building on this advanced understanding of addiction and by utilizing emerging state-of-the-art technologies we can now actually see how brain mechanisms work both under normal conditions and when affected by drugs of abuse. These tools have allowed us to cast away the old popular belief held by many that addiction is just a lot of drug use. It is not that simple. In fact, addiction is a chronic, and for many people, reoccurring disease characterized by compulsive drug seeking and use that results from the prolonged effects of drugs on the brain. These brain changes are essentially what makes addiction a brain disease. This is a conclusion reached by not just the researchers that my Institute supports, but by a number of other highly credible research-oriented sources, such as the National Academy of Sciences Institute of Medicine and the American Medical Association, among others. And as you yourselves will see shortly, from the brain image posters that I brought, the addicted brain is in fact different from the non-addicted brain.
What science has come to show as the "changed" brain of the addict is in fact what we have come to believe causes the compulsion to use drugs. Once a person becomes addicted, they become preoccupied with their quest for seeking and using drugs. The negative consequences that may result from taking the drugs are no longer an important issue for them. It is the behaviors that accompany this compulsion that are the elements responsible for the enormous health and social problems that drug addiction brings in its wake. Drug abuse and addiction have tremendous negative implications for not only the health of the individual, but for the health of the public as well. Drug use, directly or indirectly, is a major factor in crime and delinquency, work productivity, and is a vector for the spread of HIV/AIDS and other serious infectious diseases. With the most recent estimate of the economic burden for drug abuse estimated to exceed $109 billion, it is more imperative than ever that we rely on research to develop effective prevention and treatment programs that will reduce the burden of this disease. Science should also be the foundation for any health and social policy decisions that are made regarding drug use.
Science has also given us a more insightful understanding of why people take drugs. People use drugs for a variety of reasons. Some people take drugs simply to have a novel or sensational experience. They take them for the experience of modifying their mood, their perceptions, or their emotional state. But there is also another group of people who take drugs for a different reason. Although they may take drugs to modify their mood or their emotional state, they seem to be using drugs to help them cope with their problems. These individuals are, in effect, self-medicating. Whatever their initial motivation, people basically take drugs because drugs make them feel good or better immediately, and this occurs because drugs essentially change the way the brain functions. This is why we say that people take drugs because they like what they do to their brains.
However, the pleasurable effects do not last long. As the drug use continues, tolerance to the drug often develops, meaning more frequent drug use is required for the brain to register the same level of pleasure experienced during initial use. This often leads to even more prolonged drug use. And as I mentioned earlier, prolonged drug use has been found to cause pervasive changes in brain function.
This seems to be the case for almost every drug of abuse, including alcohol, nicotine, marijuana, cocaine, heroin, and methamphetamine, a problem that has reached epidemic proportions in many regions of the country. All of these drugs have been found to produce noticeable changes in the brain. Regardless of the idiosyncratic effects that each drug causes, all of these drugs have been found to elevate levels of the neurotransmitter dopamine in the brain pathways that control reward and pleasure. It is this change in dopamine that we have come to believe is a fundamental characteristic of all addictions.
Of course this is not to say that an individual has to abuse drugs for an entire lifetime for drugs to be harmful to their brains and their bodies. Acute drug use can also modify brain function in critical ways. The effects of cocaine, for example, appear immediately after a single dose. It alters the brain so the individual feels euphoric and mentally alert, especially to the sensation of sight, sound and touch. Cocaine use can also constrict blood vessels, and increase heart rate and blood pressure. Even short-term marijuana use, for example, can affect the brain, by modifying learning abilities, memory, emotional state, perception, and motor coordination. Prolonged marijuana use has been found to alter memory and learning processes, the brain, the lungs, and the immune system. And of course chronic use can lead to addiction.
I would like to use two posters to illustrate how the brain of an addict differs from those of a non- addict. Even more importantly, these images provide two dramatic examples of the long lasting effects that drugs can have on the brain. These images are particularly alarming given that both of these drugs, methamphetamine and MDMA or "Ecstasy" are being used increasingly by young adults at levels that have been found to be toxic in animals. These are the first direct images showing the effects of these drugs on the brains of humans and the effects are the same as they were in animals.
Figure 1 (right) shows images of two human brains. The one on top belongs to an individual who has never used Ecstasy. The bottom images show the brain of an individual who had used Ecstasy heavily for an extended period, but was abstinent from drugs for at least three weeks prior to the study. Clearly the brain of the Ecstasy user on the bottom has been significantly altered. The specific parameter being measured is the brain's ability to bind the chemical neurotransmitter serotonin. Serotonin is critical to normal experiences of mood, emotion, pain, and a wide variety of other behaviors. On the figure, brighter colors reflect greater serotonin transporter binding; dull colors mean less binding capacity. This figure shows a decrease in the Ecstasy user's ability to remove this important neurotransmitter from the intracellular space, thereby amplifying its effects within the brain. This decrease lasts at least three weeks after the individual has stopped using Ecstasy. Given serotonin's critical role in many behavioral characteristics, one can speculate that this abnormality of the serotonin system might be responsible for some of Ecstasy's long-lasting behavioral effects.
Figure 2(below) also demonstrates the long-lasting effects that drugs can have on the brain. Here you can see dopamine transporter binding in four different adults. Brighter colors reflect greater dopamine binding capacity. The scan on the left is that of a non-drug user, the next is of a chronic methamphetamine user who was drug free for about three years when this image was taken, followed by a chronic methcathinone abuser who was also drug free for about three years. The last image is of the brain of an individual newly diagnosed with Parkinson's Disease, a disease known to deplete dopamine in certain areas of the brain. When compared with the control on the left, one can see the significant loss in the brain's ability to transport dopamine back into brain cells. Dopamine function is critical to emotional regulation, is involved in the normal experience of pleasure and is involved in controlling an individual's motor function. Thus, this long-lasting impairment in dopamine function might account for some of the behavioral dysfunctions that persist after long-term methamphetamine use.
It is this type of scientific data that should be alarming to every citizen of this Nation. Taking drugs is not something anyone should take lightly. Even occasional drug use can be dangerous and there is no way to predict who may suffer drastic consequences as a result of experimenting with drugs. Some people are just more sensitive to the effects of drugs than others. Generally speaking, no one starts out in life saying they want to grow up to be a drug addict. And I doubt that anyone thinks that their initial decision to use drugs may be something that effects them the rest of their lives. They don't take into account that their occasional drug use may be having an effect on their brain. And I don't think anybody wants to intentionally give themselves a brain disease. These are some of the reasons that as a scientist and a public health official, it is my responsibility to inform people about what drugs can do to the brain. It is also my responsibility to inform policy makers about the science of addiction so they are able to make policy decisions that are in the public's best interests.
Thank you for the opportunity to testify at this hearing.