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Trait expectations: Another look at why addictive personality is a complete myth

In the 30 years that I have been carrying out research into addiction, the one question that I have been asked the most – particularly by those who work in the print and broadcast media – is whether there is such a thing as an ‘addictive personality’? In a previous blog I briefly reviewed the concept of ‘addictive personality’ but since publishing that article, I have published a short paper in the Global Journal of Addiction and Rehabilitation Medicine on addictive personality, and in this blog I review I outline some of the arguments as to why I think addictive personality is a complete myth.

Psychologists such as Dr. Thomas Sadava have gone as far to say that ‘addictive personality’ is theoretically necessary, logically defensible, and empirically supportable. Sadava argued that if ‘addictive personality’ did not exist then every individual would vulnerable to addiction if they lived in comparable environments, and that those who were addicted would differ only from others in the specifics of their addiction (e.g., alcohol, nicotine, cocaine, heroin). However, Sadava neglected genetic/biological predispositions and the structural characteristics of the substance or behaviour itself.

There are many possible reasons why people believe in the concept of ‘addictive personality’ including the facts that: (i) vulnerability is not perfectly correlated to one’s environment, (ii) some addicts are addicted to more than one substance/activity (cross addiction) and engage themselves in more than one addictive behaviour, and (iii) on giving up addiction some addicts become addicted to another (what I and others have referred to as ‘reciprocity’). In all the papers I have ever read concerning ‘addictive personality’, I have never read a good operational definition of what ‘addictive personality’ actually is (beyond the implicit assumption that it refers to a personality trait that helps explain why individuals become addicted to substances and/or behaviours). Dr. Craig Nakken in his book The Addictive Personality: Understanding the Addictive Process and Compulsive Behaviour argued that ‘addictive personality’ is “created from the illness of addiction”, and that ‘addictive personality’ is a consequence of addiction and not a predisposing factor. In essence, Nakken simply argued that ‘addictive personality’ refers to the personality of an individual once they are addicted, and as such, this has little utility in understanding how and why individuals become addicted.

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When teaching my own students about the concept of ‘addictive personality’ I always tell them that operational definitions of constructs in the addictive behaviours field are critical. Given that I have never seen an explicit definition of ‘addictive personality’ I provide my own definition and argue that ‘addictive personality’ (if it exists) is a cognitive and behavioural style which is both specific and personal that renders an individual vulnerable to acquiring and maintaining one or more addictive behaviours at any one time. I also agree with addiction experts that the relationship between addictive characteristics and personality variables depend on the theoretical considerations of personality. According to Dr. Peter Nathan there must be ‘standards of proof’ to show valid associations between personality and addictive behaviour. He reported that for the personality trait or factor to genuinely exist it must: (i) either precede the initial signs of the disorder or must be a direct and lasting feature of the disorder, (ii) be specific to the disorder rather than antecedent, coincident or consequent to other disorders/behaviours that often accompany addictive behaviour, (iii) be discriminative, and (iv) be related to the addictive behaviour on the basis of independently confirmed empirical, rather than clinical, evidence. As far as I am aware, there is no study that has ever met these four standards of proof, and consequently I would argue on the basis of these that there is no ‘addictive personality’.

Although I do not believe in the concept of ‘addictive personality’ this does not mean that personality factors are not important in the acquisition, development, and maintenance of addictive behaviours. They clearly are. For instance, a paper in the Psychological Bulletin by Dr. Roman Kotov and his colleagues examined the associations between substance use disorders (SUDs) and higher order personality traits (i.e., the ‘big five’ of openness to experience, conscientiousness, agreeableness, extraversion, and neuroticism) in 66 meta-analyses. Their review included 175 studies (with sample sizes ranged from 1,076 to 75,229) and findings demonstrated that SUD addicts were high on neuroticism (and was the strongest personality trait associated with SUD addiction) and low on conscientiousness. Many of the studies the reviewed also reported that agreeableness and openness were largely unrelated to SUDs.

Dr. John Malouff and colleagues carried published a meta-analysis in the Journal of Drug Education examining the relationship between the five-factor model of personality and alcohol. The meta-analysis included 20 studies (n=7,886) and showed alcohol involvement was associated with low conscientiousness, low agreeableness, and high neuroticism. Mixed-sex samples tended to have lower effect sizes than single-sex samples, suggesting that mixing sexes in data analysis may obscure the effects of personality. Dr. James Hittner and Dr. Rhonda Swickert published a meta-analysis in the journal Addictive Behaviors examining the association between sensation seeking and alcohol use. An analysis of 61 studies revealed a small to moderate size heterogeneous effect between alcohol use and total scores on the sensation seeking scale. Further analysis of the sensation seeking components indicated that disinhibition was most strongly correlated with alcohol use.

Dr. Marcus Munafo and colleagues published a meta-analysis in the journal Nicotine and Tobacco Research examining strength and direction of the association between smoking status and personality. They included 25 cross-sectional studies that reported personality data for adult smokers and non-smokers and reported a significant difference between smokers and non-smokers on both extraversion and neuroticism traits. In relation to gambling disorder, Dr. Vance MacLaren and colleagues published a meta-analysis of 44 studies that had examined the personality traits of pathological gamblers (N=2,134) and non-pathological gambling control groups (N=5,321) in the journal Clinical Psychology Review. Gambling addiction was shown to be associated with urgency, premeditation, perseverance, and sensation seeking aspects of impulsivity. They concluded that individual personality characteristics may be important in the aetiology of pathological gambling and that the findings were similar to the meta-analysis of substance use disorders by Kotov and colleagues.

More recently, I co-authored a study with Dr. Cecilie Andreassen and her colleagues in the Journal of Behavioral Addictions. We carried out the first ever study investigating the inter-relationships between the ‘big five’ personality traits and behavioural addictions. They assessed seven behavioural addictions (i.e., Facebook addiction, video game addiction, Internet addiction, exercise addiction, mobile phone addiction, compulsive buying, and study addiction). Of 21 inter-correlations between the seven behavioural addictions, all were positive (and nine significantly so). More specifically: (i) neuroticism was positively associated with Internet addiction, exercise addiction, compulsive buying, and study addiction, (ii) extroversion was positively associated with Facebook addiction, exercise addiction, mobile phone addiction, and compulsive buying, (iii) openness was negatively associated with Facebook addiction and mobile phone addiction, (iv) agreeableness was negatively associated with Internet addiction, exercise addiction, mobile phone addiction, and compulsive buying, and (v) conscientiousness was negatively associated with Facebook addiction, video game addiction, Internet addiction, and compulsive buying and positively associated with exercise addiction and study addiction. However, replication and extension of these findings is needed before any definitive conclusions can be made.

Overall these studies examining personality and addiction consistently demonstrate that addictive behaviours are correlated with high levels of neuroticism and low levels of conscientiousness. However, there is no evidence of a single trait (or set of traits) that is predictive of addiction, and addiction alone. Others have also reached the same conclusion based on the available evidence. For instance, R.G. Pols (in Australian Drug/Alcohol Review) noted that findings from prospective studies are inconsistent with retrospective and cross-sectional studies leading to the conclusion that the ‘addictive personality’ is a myth. Dr. John Kerr in the journal Human Psychopharmacology: Clinical and Experimental noted that ‘addictive personality’ had long been argued as a viable construct (particularly in the USA) but that there is simply no evidence for the existence of a personality type that is prone to addiction. In another review of drug addictions, Kevin Conway and colleagues asserted (in the journal Drug and Alcohol Dependence) there was scant evidence that personality traits were associated with psychoactive substance choice. Most recently, Maia Szalavitz in her book Unbroken Brain: A Revolutionary New Way of Understanding Addiction noted that:

“Fundamentally, the idea of a general addictive personality is a myth. Research finds no universal character traits that are common to all addicted people. Only half have more than one addiction (not including cigarettes)—and many can control their engagement with some addictive substances or activities, but not others”.

Clearly there are common findings across a number of differing addictions (such as similarities in personality profiles using the ‘big five’ traits) but it is hard to establish whether these traits are antecedent to the addiction or caused by it. Within most addictions there appear to be more than one sub-type of addict suggesting different pathways of how and way individuals might develop various addictions. If this is the case – and I believe that it is – where does that leave the ‘addictive personality’ construct?

‘Addictive personality’ is arguably a ‘one type fits all’ approach and there is now much evidence that the causes of addiction are biopsychosocial from an individual perspective, and that situational determinants (e.g., accessibility to the drug/behaviour, advertising and marketing, etc.) and structural determinants (e.g., toxicity of a specific drug, game speed in gambling, etc.) can also be influential in the aetiology of problematic and addictive behaviours. Another problem with ‘addictive personality’ being an explanation for why individuals develop addictions is that the concept inherently absolves an individual’s responsibility of developing an addiction and puts the onus on others in treating the addiction. Ultimately, all addicts have to take some responsibility in the development of their problematic behaviour and they have to take some ownership for overcoming their addiction. Personally, I believe it is better to concentrate research into risk and protective factors of addiction rather than further research of ‘addictive personality’.

As I have argued in a number of my papers and book chapters, not every addict has a personality disorder, and not every person with a personality disorder has an addiction. While some personality disorders appear to have an association with addiction including Antisocial Personality Disorder and Borderline Personality Disorder, just because a person has some of the personality traits associated with addiction does not mean they are, or will become, an addict. Practitioners consider specific personality traits to be warning signs, but that’s all they are. There is no personality trait that guarantees an individual will develop an addiction and there is little evidence for an ‘addictive personality’ that is predictive of addiction alone. In short, ‘addictive personality’ is a complete myth.

Dr. Mark Griffiths, Professor of Behavioural Addiction, International Gaming Research Unit, Nottingham Trent University, Nottingham, UK

Further reading

Andreassen, C.S., Griffiths, M.D., Gjertsen, S.R., Krossbakken, E., Kvan, S., & Ståle Pallesen, S. (2013). The relationships between behavioral addictions and the five-factor model of personality. Journal of Behavioral Addictions, 2, 90-99.

Conway, K. P., Kane, R. J., Ball, S. A., Poling, J. C., & Rounsaville, B. J. (2003). Personality, substance of choice, and polysubstance involvement among substance dependent patients. Drug and Alcohol Dependence, 71(1), 65-75.

Griffiths, M.D. (1994). An exploratory study of gambling cross addictions. Journal of Gambling Studies, 10, 371-384.

Griffiths, M.D. (1996). Behavioural addictions: An issue for everybody? Journal of Workplace Learning, 8(3), 19-25.

Griffiths, M.D. (2005). A ‘components’ model of addiction within a biopsychosocial framework. Journal of Substance Use, 10, 191-197.

Griffiths, M.D. (2009). The psychology of addictive behaviour. In: M. Cardwell, M., L. Clark, C. Meldrum & A. Waddely (Eds.), Psychology for A2 Level (pp. 236-471). London: Harper Collins.

Griffiths, M.D. (2017). The myth of ‘addictive personality’. Global Journal of Addiction and Rehabilitation Medicine, 3(2), 555610.

Hittner, J. B., & Swickert, R. (2006). Sensation seeking and alcohol use: A meta-analytic review. Addictive Behaviors, 31(8), 1383-1401.

Kerr, J. S. (1996). Two myths of addiction: The addictive personality and the issue of free choice. Human Psychopharmacology: Clinical and Experimental, 11(S1), S9-S13.

Kotov, R., Gamez, W., Schmidt, F., & Watson, D. (2010). Linking “big” personality traits to anxiety, depressive, and substance use disorders: a meta-analysis. Psychological Bulletin, 136(5), 768-821.

MacLaren, V. V., Fugelsang, J. A., Harrigan, K. A., & Dixon, M. J. (2011). The personality of pathological gamblers: A meta-analysis. Clinical Psychology Review, 31(6), 1057-1067.

Malouff, J. M., Thorsteinsson, E. B., Rooke, S. E., & Schutte, N. S. (2007). Alcohol involvement and the Five-Factor Model of personality: A meta-analysis. Journal of Drug Education, 37(3), 277-294.

Munafo, M. R., Zetteler, J. I., & Clark, T. G. (2007). Personality and smoking status: A meta-analysis. Nicotine & Tobacco Research, 9(3), 405-413.

Nakken, C. (1996). The addictive personality: Understanding the addictive process and compulsive behaviour. Hazelden, Center City, MN: Hazelden.

Nathan, P. E. (1988). The addictive personality is the behavior of the addict. Journal of Consulting and Clinical Psychology, 56(2), 183-188.

Pols, R. G. (1984). The addictive personality: A myth. Australian Alcohol/Drug Review, 3(1), 45-47.

Sadava, S.W. (1978). Etiology, personality and alcoholism. Canadian Psychological Review/Psychologie Canadienne, 19(3), 198-214.

Szalavitz M (2016). Unbroken brain: A revolutionary new way of understanding addiction. St. Martin’s Press, New York.

Szalavitz M (2016). Addictive personality isn’t what you think it is. Scientific American, April 5.

Myth world: Addictive personality does not exist

(Please note: This article is a slightly expanded and original version of an article that was first published in The Conversation).

“Life is a series of addictions and without them we die”. This is my favourite quote in the academic addiction literature and was made back in 1990 in the British Journal of Addiction by Professor Isaac Marks. This deliberately provocative and controversial statement was made to stimulate debate about whether excessive and potentially problematic activities such as gambling, sex and work can really be classed as genuine addictive behaviours. Many of us might say to ourselves that we are ‘addicted’ to tea or coffee, our work, or know others who we might describe as having addictions watching the television or using pornography. But is this really true?

The issue all comes down to how addiction is defined in the first place as many of us in the field disagree on what the core components of addiction are. Many would argue that the word ‘addiction’ or ‘addictive’ is used so much in everyday circumstances that word has become meaningless. For instance, saying that a book is an ‘addictive read’ or that a specific television series is ‘addictive viewing’ renders the word useless in a clinical setting. Here the word ‘addictive’ is arguably used in a positive way and as such it devalues the real meaning of the word.

The question I get asked most – particularly by the broadcast media – is what is the difference between a healthy excessive enthusiasm and an addiction and my response is simple – a healthy excessive enthusiasm adds to life whereas an addiction takes away from it. I also believe that to be classed as an addiction, any such behaviour should comprise a number of key components including overriding preoccupation with the behaviour, conflict with other activities and relationships, withdrawal symptoms when unable to engage in the activity, an increase in the behaviour over time (tolerance), and use of the behaviour to alter mood state. Other consequences such as feeling out of control with the behaviour and cravings for the behaviour are often present. If all these signs and symptoms are present I would call the behaviour a true addiction. However, that hasn’t stopped others accusing me of ‘watering down’ the concept of addiction.

A few years ago, Dr. Steve Sussman, Nadra Lisha and I published a large and comprehensive review in the journal Evaluation and the Health Professions examining the co-relationship between eleven different potentially addictive behaviours reported in the academic literature (smoking tobacco, drinking alcohol, taking illicit drugs, eating, gambling, internet use, love, sex, exercise, work, and shopping). We examined the data from 83 large-scale studies and reported an overall 12-month prevalence of an addiction among U.S. adults varies from 15% to 61%. We also reported it plausible that 47% of the U.S. adult population suffers from maladaptive signs of an addictive disorder over a 12-month period, and that it may be useful to think of addictions as due to problems of lifestyle as well as to person-level factors. In short – and with many caveats – our paper argued that at any one time almost half the US population are addicted to one or more behaviours.

There is a lot of scientific literature showing that having one addiction increases the propensity to have other co-occurring addictions. For instance, in my own research I have come across alcoholic pathological gamblers and we can all probably think of individuals that we might describe as caffeine-addicted workaholics. It is also very common for individuals that give up one addiction to replace it with another (which we psychologists call ‘reciprocity’). This is easily understandable as when an individual gives up one addiction it leaves a large hole in the waking lives (often referred to as the ‘void’) and often the only activities that can fill the void and give similar experiences are other potentially addictive behaviours. This has led many people to describe such people as having an ‘addictive personality’.

While there are many pre-disposing factors for addictive behaviour including genetic factors and psychological personality traits such as high neuroticism (anxious, unhappy, prone to negative emotions) and low conscientiousness (impulsive, careless, disorganised), I would argue that ‘addictive personality’ is a complete myth. Even though there is good scientific evidence that most people with addictions are highly neurotic, neuroticism in itself is not predictive of addiction (for instance, there are individuals who are highly neurotic but are not addicted to anything so neuroticism is not predictive of addiction). In short, there is no good evidence that there is a specific personality trait (or set of traits) that is predictive of addiction and addiction alone.

Doing something habitually or excessively does not necessarily make it problematic. While there are many behaviours such as drinking too much caffeine or watching too much television that could theoretically be described as addictive behaviours, they are more likely to be habitual behaviours that are important in an individual’s life but actually cause little or no problems. As such, these behaviours should not be described as an addiction unless the behaviour causes significant psychological and/or physiological effects in their day-to-day lives.

Dr. Mark Griffiths, Professor of Behavioural Addiction, International Gaming Research Unit, Nottingham Trent University, Nottingham, UK

Further reading

Andreassen, C.S., Griffiths, M.D., Gjertsen, S.R., Krossbakken, E., Kvan, S., & Ståle Pallesen, S. (2013). The relationships between behavioral addictions and the five-factor model of personality. Journal of Behavioral Addictions, 2, 90-99.

Goodman, A. (2008). Neurobiology of addiction: An integrative review. Biochemical Pharmacology, 75(1), 266-322.

Griffiths, M.D. (1996). Behavioural addictions: An issue for everybody? Journal of Workplace Learning, 8(3), 19-25.

Griffiths, M.D. (2005). A ‘components’ model of addiction within a biopsychosocial framework. Journal of Substance Use, 10, 191-197.

Griffiths, M.D. (2010). The role of context in online gaming excess and addiction: Some case study evidence. International Journal of Mental Health and Addiction, 8, 119-125.

Griffiths, M.D. & Larkin, M. (2004). Conceptualizing addiction: The case for a ‘complex systems’ account. Addiction Research and Theory, 12, 99-102.

Kerr, J. S. (1996). Two myths of addiction: the addictive personality and the issue of free choice. Human Psychopharmacology: Clinical and Experimental, 11(S1), S9-S13.

Kotov, R., Gamez, W., Schmidt, F., & Watson, D. (2010). Linking “big” personality traits to anxiety, depressive, and substance use disorders: A meta-analysis. Psychological Bulletin, 136(5), 768-821.

Larkin, M., Wood, R.T.A. & Griffiths, M.D. (2006). Towards addiction as relationship. Addiction Research and Theory, 14, 207-215.

Marks, I. (1990). Behaviour (non-chemical) addictions. British Journal of Addiction, 85, 1389-1394.

Nakken, C. (2009). The addictive personality: Understanding the addictive process and compulsive behavior. Hazelden, Minnesota: Hazelden Publishing.

Nathan, P. E. (1988). The addictive personality is the behavior of the addict. Journal of Consulting and Clinical Psychology, 56(2), 183-188.

Within you, without you: Where does addiction reside?

In 1984, Dr. Milton Burglass and Dr. Howard Shaffer published a paper in the journal Addictive Behaviors and claimed that arguably the important questions in the addiction field are ‘why do people become addicted to some things and not others?’ and ‘why some people become addicted and not others?’ Answers to these questions have been hindered by two common misconceptions about addiction, which to some extent have underpinned the ‘hard core’ disease concept of addiction. These are that addiction somehow resides within: (i) particular types of people or (ii) particular substances, and/or particular kinds of activity. That is, either some people are already ‘diseased,’ or else some substances/ activities cause this disease, or both.

There is a belief that some people are destined to become addicted. Typically this is explained in one (or both) of two ways. That some people (i.e., ‘addicts’) have an addictive personality, and that there is a genetic basis for addiction. The evidence for ‘addictive personality’ rests to a certain extent upon one’s faith in the validity of psychometric testing. Setting aside this major hurdle, the evidence in this area (as I argued with my colleagues Dr. Michael Larkin and Dr. Richard Wood in a 2006 issue of Addiction Research and Theory [ART]) is still inconclusive and contradictory.

First, psychologists have yet to determine which particular personality traits are linked to addiction. Studies have claimed that ‘the addictive personality’ may be characterized by a wide range of factors (e.g., sensation-seeking, novelty-seeking, extroversion, locus-of-control preferences, major traumatic life events, learned behaviours, etc.). The extent of this range stretches not only the notion of an ‘addictive personality’ but also the concept of ‘personality’ itself. Inevitably, much of this work relies on correlation analysis, and so the interpretation of results is not easily framed in terms of cause and effect. The approach is overly simplistic and is underpinned by a simple proposition that if we can divide people up into the right groups, then the explanation will emerge. However, addiction is far more complex than this. Of course, the relationship between individual bodies, minds, contexts, and life histories is complex and important – but it requires that we approach the matter from a more sophisticated and integrative position.

The search for a genetic basis for addiction rests upon the notion that some types of individuals are somehow ‘biologically wired’ to become addicts. In our 2006 ART paper, we argued that we must set aside any doubts about the limited conceptualization of ‘the environment’ that often typifies this kind of research, and its combination with epidemiological designs that are largely descriptive. Meta-analytic reviews have concluded that the heritability of addictive behaviour is likely to be controlled by many genes each contributing a small fraction of the overall risk. Furthermore, some of these same genes appear to be risk factors for other problems, some of them conceptually unrelated to addiction. We argued that the main point here is that while these findings do contribute something to our understanding of ‘why some people and not others,’ they do not adequately or independently explain the range of variation. Therefore the most we can say is that some people are more likely to develop problems under certain conditions, and that given the right conditions most people could probably develop an addiction. Emphasis needs to be placed on identifying those ‘conditions,’ rather than on searching for the narrowest of reductionist explanations.

We also argued in our 2006 ART paper that substances and activities cannot be described as intrinsically addictive in themselves (unless one chooses to define ‘addictive’ in terms of a substance or behaviour’s ability to produce tolerance and/or withdrawal, and to ignore the range of human experience that is excluded by this). Biologists may be able to tell us very valuable things about the psychopharmacological nature of the rewards that particular substances and behaviours provide, and the different kinds of neuroadaptation that they may or may not produce in order to effect tolerance and/or withdrawal. But we argue that this on its own, is not an adequate explanation for addiction. In 1975, Dr. Lee Robins’ classic study (in the Archives of General Psychiatry) of heroin-users returning from the Vietnam war is one example of the evidence that refutes this oversimplification. This study clearly highlighted the importance of context (i.e., that in a war zone environment individuals were addicted to heroin but on return to civilian life the addiction ceased to exist), and the framework provided by such contexts for making sense of addiction. In a hostile and threatening environment, opiates clearly provided something not usually required by most people; and given a cultural environment in which opiate use is a commonplace, and opiates are available, then opiate use ‘makes sense’. This study provides support for the assertion that some people are more likely to become addicted under some conditions, and that given the right conditions perhaps many people could understand what it means to be an addict.

So, with regard to the question, ‘why some individuals/addictions and not others?’ the rewards associated with various activities may be qualitatively very different, and may not necessarily be inherent or unique to a particular activity or substance, either. Many rewarding activities are rewarding because they present individuals with opportunities to ‘shift’ their own subjective experience of themselves (for example, see the research on Ecstasy use and bungee jumping that I published with Dr. Michael Larkin in a 2004 issue of the Journal of Community and Applied Social Psychology).

Frequently, a range of such opportunities is offered to the experienced user. Dr. Howard Shaffer (in a 1996 paper in the Journal of Gambling Studies) has pointed out that those activities that can be most relied upon to shift self-experience in a robust manner are likely to be the most popular – and (as a consequence) to be the most frequent basis of problems. So, obviously, our understanding of the available resources for mood modification must play a major part in understanding addiction. However, we must make a careful distinction between describing some substances as being more ‘robust shifters of experience’ than others (as we advocated in our 2006 ART paper) and describing some substances as ‘more addictive’ than others (which we argued against).

Dr Mark Griffiths, Professor of Gambling Studies, International Gaming Research Unit, Nottingham Trent University, Nottingham, UK

Further reading

Burglass, M.E. & Shaffer, H.J. (1984). Diagnosis in the addictions I: Conceptual problems. Addictive Behaviors, 3, 19-34.

Griffiths, M.D.  (2005). A ‘components’ model of addiction within a biopsychosocial framework. Journal of Substance Use, 10, 191-197.

Griffiths, M.D. (2011). Behavioural addiction: The case for a biopsychosocial approach. Transgressive Culture, 1(1), 7-28.

Griffiths, M.D. & Larkin, M. (2004). Conceptualizing addiction: The case for a ‘complex systems’ account. Addiction Research and Theory, 12, 99-102.

Larkin, M., Wood, R.T.A. & Griffiths, M.D. (2006). Towards addiction as relationship. Addiction Research and Theory, 14, 207-215.

Orford, J. (2001). Excessive Appetites: A Psychological View of the Addictions (Second Edition). Chichester: Wiley.

Robins, L.N, Helzer, J.E, & Davis, D.H (1975) Narcotic use in Southeast Asia and afterward. Archives of General Psychiatry, 32, 955-961.

Shaffer, H. J. (1996). Understanding the means and objects of addiction: Technology, the Internet, and gambling. Journal of Gambling Studies, 12, 461–469.

Tyndale, R.F. (2003). Genetics of alcohol use and tobacco use in humans. Annals of Medicine, 35(2), 94–121.

Walters, G. D. (2002). The heritability of alcohol use and dependence: A meta-analysis of behavior genetic research. American Journal of Drug and Alcohol Abuse, 28, 557–584.