Addressing Criticisms of the Disease Model

Volkow, Koob, and McLellan on the neurobiology of addiction.

The New England Journal of Medicine recently published a review article, “Neurobiologic Advances from the Brain Disease Model of Addiction,” authored by three prominent figures in the field of addiction research: Nora Volkow, the director of the National Institute of Drug Abuse (NIDA); George Koob, the director of the National Institute of Alcohol Abuse and Alcoholism (NIAAA); and Thomas McLellan, founder and chairman of the Treatment Research Institute in Philadelphia.  The article summarizes the research that has “increasingly supported the view that addiction is a disease of the brain,” and concludes that “neuroscience continues to support the brain disease model of addiction.”

The implications of this, say the authors, are straightforward: “As is the case in other medical conditions in which voluntary, unhealthful behaviors contribute to disease progression (e.g., heart disease, diabetes, chronic pain, and lung cancer), evidence-based interventions aimed at prevention, along with appropriate health policies, are the most effective ways of changing outcomes.”

And some of the implications are immediate: “A more comprehensive understanding of the brain disease model of addiction many help to moderate some of the moral judgement attached to addictive behaviors and foster more scientific and public health-oriented approaches to prevention and treatment.”

In a supplementary appendix, the authors address some of the common criticisms of the disease model of addiction, and offer counter-arguments. The quotes below are excerpted directly from the appendix.

—Most people with addiction recover without treatment, which is hard to reconcile with the concept of addiction as a chronic disease.

This reflects the fact that the severity of addiction varies, which is clinically significant for it will determine the type and intensity of the intervention. Individuals with a mild to moderate substance use disorder, which corresponds to the majority of cases, might benefit from a brief intervention or recover without treatment whereas most individuals with a severe disorder will require specialized treatment

—Addicted individuals respond to small financial rewards or incentives (contingency management), which is hard to reconcile with the notion that there is loss of control in addiction.

The demonstrated effectiveness of contingency management shows that financial cues and incentives can compete with drug cues and incentives – especially when those financial incentives are significant and relatively immediate; and when control has been simply eroded rather than lost. Contingency management is increasingly being utilized in the management of other medical disorders to incentivize behavioral changes (i.e., compliance with medications, diets, physical activity).

—Gene alleles associated with addiction only weakly predict risk for addiction, which is hard to reconcile with the importance of genetic vulnerabilities in the Brain Disease Model of Addiction.

This phenomenon is typical of complex medical diseases with high heritability rates for which risk alleles predict only a very small percentage of variance in contrast to a much greater influence of environmental factors (i.e., cirrhosis, diabetes, asthma, cardiovascular disease). This reflects, among other things, that the risk alleles mediate the response to the environment; in the case of addiction, the exposures to drugs and stressful environments.

Overlaps in brain abnormalities between people with addiction and control groups raises questions on the role that brain abnormalities have on addiction.

The overlap is likely to reflect the limitation of currently available brain imaging techniques (spatial and temporal resolutions, chemical sensitivity), our limited understanding of how the human brain works, the complexity of the neurobiological changes triggered by drugs and the heterogeneity of substance use disorders.

Treatment benefits associated with the Brain Disease Model of Addiction have not materialized.

Medications are among the most effective interventions for substance use disorders for which they are available (nicotine, alcohol and opiates). Moreover, progress in the approval of new medications for substance use disorders has been slowed by the reluctance of pharmaceutical companies to invest in drug development for addiction.

Benefits to policy have been minimal.

The Brain Disease Model of Addiction provided the basis for patients to be able to receive treatment for their addiction and for insurances to cover for it. This is a monumental advance in health policy. The Brain Disease Model of Addiction also provides key evidence-based science for retaining the drinking age at 21 years.

NIDA’s Volkow Defends New Medications for Addiction

On Big Data, Big Vaccines, and a Big New Agency.

In her Director’s Report to the 2011 meeting of the College on Problems of Drug Dependence in San Diego last week, Dr. Nora Volkow, director of the National Institute on Drug Abuse, sought to refute allegations that NIDA lately has been too focused on pharmacological approaches to treating addiction—“magic bullets” in the form of pills or vaccines. Dr. Volkow presented figures showing, as the CPDD Community Website reported, that “NIDA funding allocation for new medication development has remained stable at about 12% for some time, despite concerns expressed by some researchers that funding in other areas is being sacrificed to support the medication development portfolio.” Basic and clinical neuroscience research accounts for 45% of expenditures, she said.

In other news, Volkow expressed her avid interest in the possibilities presented by so-called “big dataset science”—the act of pooling together huge amounts of data in order to generate greater statistical power. She traced a set of disciplines—genetics, epigenetics, proteomics, brain imaging, clinical data, and systems biology—and said that the NIH’s Working Group on Data and Informatics  was seeking systematic ways of integrating and analyzing large biomedical datasets in these crucial areas.

As for treatment, the current emphasis is on stimulants. Volkow said that work continues on finding reliable antagonist drugs to combat the dopamine disruptions promoted by active drug abuse. She suggested that work on buspirone, the D3 receptor antagonist and partial serotonin 5HT agonist used to treat generalized anxiety disorder, has shown that it may reduce cocaine self-administration in rhesus monkeys. This would be of considerable clinical interest, since addiction medicine presently has no effective drug treatments to offer for stimulants like cocaine and methamphetamine. A large clinical study now underway is showing that buspirone blocked D3 receptors in monkey brains in a way that reduced their interest in cocaine.

And she referred to the failed promise of NicVax, the short-lived vaccine for cigarette addiction. The treatment “failed to meet the primary endpoint in Phase II trials.” In other words, it flunked out. Only 30% of addicted smokers developed sufficient antibodies from NicVax to do them any good. But she cited new research on an alternative approach to vaccines, including a new cocaine vaccine (dAd5GNE) shown to be effective in reducing cocaine addiction-related behaviors in rats through the long-term blockade of dopamine transporters.

In a related approach to producing a reliable anti-cocaine antibody, researchers in the Department of Genetic Medicine at Weill Cornell Medical College went to work on “an adeno-associated virus (AAV) gene transfer vector as the delivery vehicle to persistently express an anti-cocaine monoclonal antibody in vivo, which would sequester cocaine in the blood, preventing access to cognate receptors in the brain.” An AAV is a small virus that is infectious but not pathogenic in humans. You might have it right now, but wouldn’t know it, since AAV doesn’t cause disease. So, the researchers used an AAV to build a transporter mechanism for their monoclonal antibody, GNC92H2. In mice, the result was “persistent serum levels of high-affinity, cocaine-specific antibodies that sequestered intravenously administered cocaine in the blood.”

And finally, while the name is still up in the air, a new national institute combining the study of alcohol and the study of all other addictive drugs will follow after final recommendations submitted to NIH Director by year’s end. Volkow briefly laid out the timeline of the merger for the assembled scientists. Call it the Institute for Substance Use Disorders, or the Institute for Addiction Disorders, or the National Institute of Substance Abuse, but whatever the eventual name, it will be fully operational by late 2013, or at least that’s the plan—and Nora Volkow, the current director of the NIDA, which will merge with, or rather absorb, the National Institute on Alcohol Abuse and Alcoholism (NIAAA), won’t be its director (See "NIH Turf Wars"). Whether that’s good or bad is the subject of much debate, but the project marches on, and seems sensible in the end.