STIMULATING DEBATE IN THE FIELD OF ADDICTION

We are pleased that our paper [1] has served its intended purpose in stimulating discussion about the relevance of dopamine dysregulation syndrome (DDS) to the addiction field.

We agree with Brown & Lawrence's suggestions about approaches to researching DDS that may cast more light on it and its relationship to stimulant addiction [2]. Specification of standardized diagnostic criteria for DDS is critical to align diagnoses of the syndrome with those in the proposed DSM-5 classification, and prospective neuroimaging studies may identify biomarkers that predict the risk that patients with Parkinson's disease (PD) may develop DDS.

Dagher agrees that there is a good case for including compulsive levodopa (l-dopa) abuse in patients with PD under the label of addiction [3]. He also describes other forms of addictive behaviour, such as problem gambling and hypersexuality, that have been reported in PD patients treated with dopamine agonists [4–6]. Dagher suggests some useful hypotheses about the possible roles played by the differential actions of l-dopa and dopamine agonists on different brain dopamine receptors. This type of research may lead to a better understanding of compulsive behaviour in PD, facilitate the development of more effective treatments for DDS and possibly help scientists and clinicians to understand more clearly the neurobiology of stimulant addiction.

Kaye notes similarities between the debates over whether compulsive use of l-dopa is a form of drug dependence and earlier debates about the validity of cannabis, amphetamine, cocaine and 3,4-methylenedioxymethamphetamine (MDMA) dependence syndromes [7]. She suggests that recognition of DDS abuse as a form of addiction may assist to destigmatize illicit drug dependence, which can be also seen as arising from the use of illicit stimulants to self-medicate distress.

We did not intend, as Soyka assumes, to advocate for the inclusion of DDS in the DSM-5 [8]. We agree that this would be premature given the state of the evidence. What we did propose was that research be undertaken to test the hypothesis that DDS is a form of addiction that resembles stimulant addiction and that may thereby ‘be usefully classified as a form of addiction’ (Ambermoon et al. [1], p. 244). We agree that DDS is a much smaller public health problem than iatrogenic dependence on pharmaceutical opioids and benzodiazepines, but as Kaye notes, DDS need not be a highly prevalent disorder to be of clinical and theoretical interest. DDS can be a severely debilitating condition in a significant minority of PD patients and warrants attention for this reason. As we argued, there are in addition good theoretical reasons why addiction scientists should pay more attention to these disorders.