Since the 1980’s there
is awareness that psychiatric disorders can co-occur with
intellectual disabilities (ID) (Sovner and Hurley,
1983, Cooper et al., 2007, Hermans et al., 2013, Marston et al., 1997, Hurley,
2008). Nowadays, we know that depression is a common
psychiatric disorder in adults with ID. The prevalence range of depression in
the ID population varies from 2.2% to 7.6% (Cooper et al., 2007,
Deb et al., 2001, Hermans et al., 2013, Smiley, 2005). The prevalence is even higher compared to the
general population, despite the fact that depressive symptoms can be difficult
to recognize in this population (Hurley, 2008, Marston
et al., 1997, Hermans et al., 2013). Depression is mainly characterised by sadness and loss of interest or
pleasure (American
Psychiatric Association, 2013). Depression has a major impact on the
quality of life and leads to cognitive, social and physical problems (Bijl and
Ravelli, 2000, Beekman et al., 2002, Sprangers et al., 2000, Hays et al., 1995,
Alonso et al., 2004, Coryell et al., 1993, Judd et al., 2008, Rand and Malley, 2017, Kober, 2010).

Psychoactive medications, including antidepressant medications, are
regularly prescribed in adults with ID, primarily to
reduce challenging behaviour (Lott et al., 2004,
Matson and Mahan, 2010, Sheehan et al., 2015).  There is some
evidence that antidepressant medication can decrease depressive symptoms in
adults with ID (Janowsky et al., 2005,
Masi et al., 1997, Verhoeven et al., 2001). Negative side effects (short term and
long term) can appear when psychoactive medications are used in adults with ID (Matson and Mahan,
2010, Mahan et al., 2010, Hä?ler et al., 2015).  For example,
physical complaints, neurological damage, movement side effects and
physiological problems are mentioned (Matson and Mahan,
2010, de Leon et al., 2009, Sheehan et al., 2017). Besides, adults with ID seem to be more amenable to
develop side effects compared to the general population when psychoactive
medications are used (Arnold, 1993, Matson
and Mahan, 2010, Sheehan et al., 2017). Moreover, it can take a while for a psychoactive
medication to work in the right daily dosage and adults with ID may experience even
more side effects when more than one psychotropic medication is used (Matson and Mahan,
2010). Furthermore, many adults with ID use more than one
medication and polypharmacy is common in adults with ID (Bowring et al., 2017,
Hä?ler et al., 2015, Haider et al., 2014). Therefore, there is a need for evidence based
non-pharmacological treatments for depression in adults with ID. 

In the general
population, a wide range of systematic reviews on non-pharmacological
interventions for depression have been published over the last couple of years (Catalan-Matamoros
et al., 2016, Cox et al., 2012, Merry et al., 2011, Kvam et al., 2016, Lee et
al., 2016, Stubbs et al., 2016). Unfortunately, the conclusions of these
reviews (both positive and negative) cannot be generalised to the ID population
because a large part of the non-pharmacological interventions for depression of
the general population are not suitable for adults with ID. Besides the
cognitive limitations, adults with ID frequently have verbal and physical
limitations as well.  So, for example,
exercise interventions can be too complicated to perform or physically
impossible. Physiological interventions, for example CBT, are too difficult for
adults with a more severe ID and for those with verbal limitations.