Major depressive disorder (MDD) is one of the most prevalent psychiatric disorders characterized by high relapse and/or recurrence rates. Relapse is defined as ‘a return of symptoms satisfying the full syndrome criteria for an episode that occurs during the period of remission, but before recovery’, where remission is a period in which the individual no longer meets syndrome criteria for the disorder and has no more than minimal symptoms, and recovery is being in remission for 6 months or longer; recurrence is ’ the appearance of a new episode of MDD occurring during recovery’ [
1]. In a large prospective study, a recurrence rate of 85% was observed in outpatients with MDD during a follow-up period of 15 years [
2]. Furthermore, the recurrence risk has been shown to increase with 16% after each successive episode [
3]. Given the high psychological as well as social and economic burden associated with MDD, relapse/recurrence prevention is extremely important. The most commonly used strategy to prevent relapse/recurrence is maintenance treatment with antidepressant medication (mADM). International guidelines recommend that patients with recurrent MDD should continue mADM for at least two years after remission [
4]. A meta-analysis showed that mADM reduces relapse/recurrence rates significantly compared to placebo (18% versus 41%) based on 31 randomized controlled trials with follow-up periods ranging from 6 to 36 months [
5]. However, despite the established effectiveness of mADM as a preventive strategy, it has several disadvantages. First, many patients are unwilling to continue mADM for a longer period [
6] and adherence is typically low [
7]. Second, many patients experience disturbing side effects [
8]. Moreover, many patients prefer psychological over pharmacological treatment [
9]. Psychotherapeutic approaches also seem to have long-term beneficial effects, whereas effects of mADM cease after discontinuation [
10]. To address the need for psychological interventions targeting relapse prevention, Segal, Williams and Teasdale developed Mindfulness-Based Cognitive Therapy (MBCT) [
11]. The aim of MBCT is not to change or eliminate depressive symptoms, but rather to relate to them in a different way, i.e. with a more accepting, mild attitude. The rationale behind the MBCT program is based on an empirically supported, theoretical framework suggesting that patients with recurrent depression become more vulnerable to developing depression as cognitive reactivity increases (for a review see [
12]). Cognitive reactivity refers to negative modes of thinking and behaving that are reactivated in periods of stress or low mood. It is suggested that these (automatic) negative reactions in turn, lead to a further lowering of mood, eventually turning into a depressive relapse/recurrence [
13]. Cognitive reactivity is strongly related to rumination, which refers to recurrently thinking about one’s depressive symptoms and their possible causes and implications. Rumination is thought to be an important cognitive vulnerability factor for both onset and relapse/recurrence in depression [
14,
15]. MBCT is targeted at recognizing these cognitive and behavioral reactions to low mood or other stressful situations, and to observe these reactions with acceptance and kindness and from a wider, decentered perspective. Indeed, there is evidence that MBCT diminishes the ‘toxic’ relationship between post-treatment cognitive reactivity and depressive relapse [
16] and that decreased rumination mediates the effects of MBCT [
17]. Unlike cognitive reactivity and rumination, self-compassion seems to be a beneficial factor that is protective against depression. Self-compassion can be described as a combination of (a) self-kindness - being kind and understanding toward oneself in instances of pain or failure, (b) common humanity - perceiving one’s experiences as part of the larger human experience, and (c) mindfulness - holding painful thoughts and feelings in balanced awareness [
18]. Evidence suggests that both self-compassion and mindfulness skills mediate the effect of MBCT on relapse/recurrence [
16]. Three randomized controlled trials (RCTs) have shown that MBCT in addition to treatment as usual (TAU) significantly reduced the relapse/recurrence risk compared with TAU alone, over a period of 14 months [
19‐
21]. In the first two trials [
19,
20], beneficial effects of MBCT were seen in patients with three or more past episodes, whereas no difference in relapse/recurrence percentages between MBCT and TAU was observed in patients with two past episodes (but see [
22] for positive effects of MBCT in patients with one or two past episodes). Another trial has shown that MBCT’s prophylactic effect is at least equal to mADM for patients with three or more past episodes [
23]. This latter finding may specifically apply to patients whose remission is unstable [
24]. There is also evidence that MBCT might reduce subthreshold depressive symptoms, an important risk factor for relapse/recurrence, in patients remitted from MDD [
22] and patients with current MDD [
17]. A recent meta-analysis [
25] showed that the overall risk ratio for relapse/recurrence after MBCT is 0.66 (a relative risk reduction of 34%) compared with TAU or placebo indicating that MBCT is indeed an effective prophylactic intervention for patients with recurrent MDD in remission. However, the prophylactic effectiveness of the
combination of MBCT plus mADM has not yet been compared with either mADM or MBCT on their own. More specifically, MBCT has not been studied as an additional treatment in patients continuing mADM, rather than TAU, to prevent relapse/recurrence. Also, up to now we do not know if continuing mADM after MBCT has additional benefits over withdrawing from mADM after MBCT. As more and more MBCT courses are available, answering these specific questions becomes increasingly important for patients and clinicians in order to find the optimal strategy to prevent relapse/recurrence. The current study is designed to answer these questions.