Treatment seeking for alcohol and drug use disorders by immigrants to the Netherlands

Since differential levels of social adversity may explain the ethnic pattern for schizophrenia, we tested the hypothesis that the pattern for DUD is similar. As expected, the risk of a first treatment for a DUD was higher for male immigrants from Surinam, the Dutch Antilles and Morocco and lower for female immigrants from Morocco and for immigrants of either gender from Turkey. The results for women from Surinam and the Netherlands Antilles were contradictory, namely a higher risk of treatment for DUD according to the national data and a lower risk according to the Rotterdam data. Remarkably, immigrants from almost all non-western countries had a lower risk of a first treatment for an AUD than Dutch nationals.

Our study was based on complete information from all Dutch hospitals (national data), all inpatient- and outpatient clinics in Rotterdam (Rotterdam data) and reliable denominators. The denominators did not include small numbers of illegal immigrants, but there is no evidence that they are at a high risk of developing a substance use disorder. The prevailing idea is that they behave inconspicuously, from fear of being detected and expelled.

The accuracy of the data on country of birth has not been examined. However, since the responsible physician, psychologist, nurse or social worker, who knew the patient well, provided this information, it was probably in most cases correct. Furthermore, “country of birth” is not always synonymous with ethnic origin. Some Dutch nationals were second-generation immigrants, but most of them were younger than 20 during the study period. Finally, our study did not regard outpatient facilities in other places than Rotterdam.

The registries could not provide information on the time when the patient developed the disorder. However, the physicians who treated the Surinamese, Dutch Antillean, Turkish, and Moroccan immigrants stated that most patients developed the DUD after their arrival in the Netherlands. The higher risk of DUDs among western immigrants, in contrast, is almost certainly because these individuals already had the disorder before immigrating and sought drugs or treatment in the Netherlands. A survey in Amsterdam revealed that only 4 of 369 western immigrants had developed their DUD in the Netherlands [4]. Many German heroin prostitutes, for example, came for treatment with methadone.

It is very likely that the results presented here do not equate to true incidence rates. A high proportion of heroin addicts (62–81%) do come in contact with the Dutch services [11], but this is probably not true for people addicted to other drugs or to alcohol. It may be noteworthy here that cannabis is the most popular drug of misuse, not heroin [1].

Consequently, an important question concerns the true differences in the risk of developing a disorder. Bearing in mind that there is evidence that non-western immigrants are more likely to avoid AUD or DUD services than Dutch nationals are [13, 28], there is probably a real increase in the risk of developing a DUD among male immigrants from Surinam, the Antilles and Morocco, and the true increase could even be greater. Similarly, the decrease in risk among immigrants from Turkey or Cape Verde may in reality be non-existent.

We have no ready explanation for the contradictory findings on the risk of DUD among female immigrants from Surinam and the Dutch Antilles. Firstly, it is possible that they avoid the treatment facilities in Rotterdam. Secondly, a history of migration from Surinam or the Dutch Antilles may be a risk factor for a more severe form of the disorder, which requires hospitalisation. Finally, it is possible that their true risk of developing DUD is not increased and that they are less “successful” than Dutch women in avoiding hospitalisation. The latter mechanism could explain the increased risk of a first hospitalisation seen in the national data.

The results presented here may be influenced by many factors, including the patterns of substance use in the countries of origin and destination, selective migration, and thresholds for contacting the relevant services. A previous study concluded that the prevalence of AUD in the country of origin was a strong determinant of the frequency in immigrants [15]. However, it is still uncertain whether the reported international differences in prevalence rates are real or result from measurement error [20]. The low risk of AUDs among immigrants from Turkey and Morocco is probably due to the Islamic religion. A Turkish study reported a low prevalence of alcohol abuse in Istanbul [2].

It is possible that the increased risk in certain immigrant groups is due to selective migration of genetically predisposed individuals, but there have been no studies of this. Selective migration is unlikely to be the sole explanation for the higher risk of a DUD among immigrants from Surinam, because more than a third of the population emigrated shortly after the country became independent.

Since immigrants are over-represented in the urbanized areas of the Netherlands and since urban residence has been found to be associated with a higher risk for the development of AUDs and DUDs [26], one could argue that some findings for migrants obtained with the national data are not a reflection of their ethnic minority status, but a manifestation of the urban effect. Indeed, the relative risks for several immigrant groups were lower in the Rotterdam data than in the national data. However, confounding by urbanicity cannot have played a role in the Rotterdam data-set, where all citizens were exposed to the urban factor. Furthermore, it is likely that urban residence is both a cause and a consequence of the development of a DUD, because many patients move to cities, where illicit substances are more readily available.

As expected, the ethnic pattern for DUDs, in particular the low risks among male immigrants from Turkey and the high risks among male immigrants from Surinam, the Dutch Antilles and Morocco, bears a striking resemblance to the ethnic pattern for schizophrenia. The risk of schizophrenia for immigrants from Cape Verde has been addressed by a single prevalence study in Rotterdam, which found no increased rate for Cape Verdian men and a twofold increased rate for Cape Verdian women [7]. Consequently, the results for male immigrants from Cape Verde are in line with our hypothesis, those for female immigrants are not. How to explain the similarities in ethnic patterns, especially among males?

The relative risks for immigrants from non-western countries might be decreased by adjustment for social class, but unfortunately we did not dispose of the required data to do this. However, social class does not explain the ethnic pattern among the immigrant groups of this study, because Turkish immigrants have a lower educational level and income than Surinamese and Dutch Antillean immigrants [19]. It is also worthwhile to note that the relationship between social class and risk for substance use disorders is not straightforward and may depend on the definition of social class. A large study in Israel found a lower risk for people of high socio-economic status, when this was defined in terms of educational level, income and occupational prestige, but a higher risk for people who have more control over their workplace: ownership, control over budget decisions, control over other workers and control over one’s own work [29].

It is also unlikely that the pattern is explained entirely by genetic factors, because Cape Verdians, who are at a low risk, originate from the same part of Africa as the Afro-Surinamese and Dutch Antilleans.

Since use of cannabis and some other drugs increases the risk of schizophrenia [14], one could hypothesise that the increased schizophrenia risks for certain immigrant groups are due to higher rates of drug abuse. However, studies examining drug abuse in patients with a first episode of schizophrenia have failed to find higher rates in African-Caribbeans in the UK or in immigrants to the Netherlands [6, 27].

The chronic experience of social defeat has recently been hypothesised to be a risk factor for both substance use disorders and schizophrenia [22]. Experiments in rats have shown that repeated episodes of social defeat led not only to an increased self-administration of amphetamine and cocaine, but also to amphetamine sensitisation, i.e., an enhanced behavioural and dopamine response to amphetamine [10]. Previously untreated schizophrenic patients exhibit amphetamine sensitisation too [18] and resemble, in this respect, defeated animals. It is possible, therefore, that the subordinate or outsider position of many immigrants contributes to their high risks of substance use disorders and schizophrenia. The social cohesion among Turkish and Cape Verdian immigrants to the Netherlands, who distinguish themselves from other immigrant groups by their strong social and family networks and a strong, positive identification with their own culture [7, 17] may be a protective factor. Cape Verdians are known as “silent immigrants”, because they do not complain and do not cause many problems. Moreover, the stability of the Turkish community is reflected by the lower crime rate among Turkish immigrants compared with their Moroccan, Dutch Antillean or Surinamese counterparts [16]. The results of a study in London, which demonstrated that the incidence of schizophrenia in non-white ethnic minorities is greater when they comprise a smaller proportion of the local population, support these ideas [3].

However, not all of the findings are completely in line with our hypothesis. On the basis of the social defeat hypothesis one would expect high risks of AUDs among immigrants from the non-Islamic countries of Surinam and the Dutch Antilles, but this study only found an increased risk for Dutch Antillean-born males in the national data. Perhaps a preference for either alcohol or drugs is explained by cultural factors.

In conclusion, this study showed similarities between the ethnic pattern for DUD and that for schizophrenia. However, further research is needed to investigate whether these similarities also occur in other countries and whether they are due to the experience of social defeat or to other factors.