A Short History of Psychotherapy Research

Today, many people may find the relevance of psychological treatment in mental health care to be all but self-explanatory. Psychological therapies are now delivered all around the world, and recent WHO guidelines strongly recommend their implementation for six mental disorder groups, especially in low- and middle-income countries (LMICs; WHO, 2023). In many Western countries, psychological therapies are an established part of routine care for many decades. This “success story” hides the fact that psychotherapy, as conceived today, is a fairly new invention. Its empirical investigation is even younger, and did not emerge before the middle of the 20th century.

In his seminal work on the history of psychiatry, Ellenberger (1994, chap. 2) traces back the origins of psychological treatment to 18th century “animal magnetism”. This movement was associated with figures such as Franz Mesmer (1734-1815) and the Marquis de Puységur (1751-1825). Deeply non-scientific by modern standards, animal magnetism focused on the role of a “magnetizer” or “mesmerizer”, who would use eye contact, hand gestures, or magnets to reestablish the proper flow of “magnetic life fluids” (Lebensmagnetismus) to resolve patients' psychological distress (Lopez, 1993; Schott, 2005).

In some individuals, this treatment would cause a state of altered consciousness or trance. Leaving behind Mesmer’s magnetic theory, it was increasingly recognized that this trance could be induced by suggestion alone, and could be harnessed for therapeutic intervention (Hull, 1929; Perry, 1978). This led to the development of 19th century Hypnotism, which conceptualized trance as a type of artificially induced somnambulism (Ellenberger, 1994, p. 71, 90, 101).

The developments starting with Mesmer have been described as a “psychological turn” (Crabtree, 2019). Mesmerism and Hypnotism contained ideas that remain influential in psychodynamic theory today: first, the powerful and suggestive relationship (“rapport”) between the “therapist” (Mesmerizer, Hypnotizer) and their patient (Ellenberger, 1994, p. 76); as well as dipsychism, the notion that the human mind contains a second, subconscious layer malleable by intervention (Abramowitz & Torem, 2018, Ellenberger, 1994, p. 145).

It is this intellectual context that Pierre Janet (1859-1947), Josef Breuer (1842-1925), Sigmund Freud (1856-1939) and others built and expanded on, ultimately leading to the development of psychoanalysis, and of psychodynamic psychotherapy. With many extensions and revisions in the 20th century, this type of treatment remains relevant in patient care until today.

Another strand of psychotherapy research can be traced back to the origins of behavioral psychology. Ivan Pavlov’s (1849-1936) groundbreaking research on classical conditioning (Windholz, 1997), or Watson’s “Little Albert” study (see Fridlund et al., 2012; Harris, 1979, for a critical summary) described methods to induce “experimental neurosis” without resorting to any mentalistic theory. Wampold and Imel (2015, p. 20) see a first attempt to leverage conditioning for therapeutic means in the works of Joseph Wolpe (1915-1997).

Like other influential figures in behavioral therapy, Wolpe was a psychiatrist who become dissatisfied with psychoanalysis, and turned to learning theory instead. In “Psychotherapy by Reciprocal Inhibition” (1968), Wolpe described his method of systematic desensitization, in which patients are subjected to fear-provoking stimuli, which are then conditioned by progressive relaxation. In behavioral therapies, such exposure techniques have remained a quintessential tool in the treatment of anxiety disorders (Craske et al., 2014).

Behavioral therapies were further enriched by the “cognitive turn” in the mid-20th century. Aaron Beck (1921–2021) and Albert Ellis (1913–2007) highlighted the importance of challenging automatic thoughts and irrational beliefs in psychotherapy, particularly for treating depression (Dowd, 2004; Rosner, 2014). In recent decades, cognitive-behavioral therapies were further enhanced by “third-wave” approaches, which putting greater emphasis on cognitive processes instead of their particular content, and including mindfulness and acceptance-based techniques (Hayes & Hofmann, 2021).

There are also other traditions that influenced modern psychotherapy, even though their contribution may be less commonly known. In the United States, for example, “talk therapies” with a spiritual background were immensely popular at the turn of the 19th century (Wampold & Imel, 2015, p. 17). Introduced in 1906, the Emmanuel movement in Boston was a first attempt to combine medical practice with individual and group therapies aimed at improving patients' mental health, including those with less than severe mental disorders (e.g., depression, anxiety, or alcohol dependence; Caplan, 1998).

There is also a rich history of humanistic treatments, emphasizing the unique experience and self-determination of each patient, as well as the importance of universal positive regard. This includes logotherapy, the “Third Viennese school” of psychotherapy founded by Viktor Frankl (Pytell, 2001); Carl Rogers' person-centered therapy (Kirschenbaum & Jourdan, 2005); or Gestalt therapy (Wagner-Moore, 2004). Some techniques of these schools continue to be practiced today, even if under the umbrella of “eclectic” and modern cognitive-behavioral treatments (Fernández-Álvarez & Fernández-Álvarez, 2019).

The history of psychotherapy is often presented in the way I did in the preceding sections; i.e., as a line of competing theories and resulting techniques that a trained therapist should or should not implement in a specific, face-to-face setting. But there is also a “second” history, arguably less commonly told, revolving around psychotherapy’s connection with technology.

Starting from the 1940s, for example, Rogers' group already used audiotapes to generate and test hypotheses, and to train new counsellors (Rogers, 1942). The value of administering psychotherapy via telephone has already been underlined in the 1960s (Rosenblum, 1969), and there is now robust evidence supporting its efficacy (Castro et al., 2020). There is a long, albeit underrepresented tradition in which technological advances were used to provide psychotherapeutic contents outside the “classic” face-to-face setting, including bibliotherapy and other forms of self-guided treatment (Cuijpers, 1997; Jack & Ronan, 2008).

Lewinsohn’s “Coping with Depression” course (Lewinsohn & Clarke, 1984), for instance, has been publicly disseminated through technological means early on, including via personal computers, CD-ROMs, or television (Cuijpers et al., 2009). The efficacy of this approach in treating and preventing depression has been demonstrated in many studies (ibid.).

These technological advances have culminated in the proliferation of Internet-based interventions, arguably one of the more consequential developments in psychotherapy research within the last two decades. The effects of Internet and smartphone-based interventions has since been demonstrated in hundreds of clinical trials (Moshe et al., 2021), and digital therapies are now a part of routine care in many countries. In the future, recent advances in cloud computing and sensor technology may improve the scope and flexibility of these interventions even further. I will return to this topic later (see “Methodological Innovations” section).

In the beginning of the 20th century, the dominant format to examine psychotherapy effects was the case study (Strupp & Howard, 1992). Such examinations had a particular importance among psychoanalytic researchers, and include famous examples such as Breuer’s “Anna O.” (Reeves, 1982) or Freud’s “Little Hans” (Wolpe & Rachman, 1960). Clinical case descriptions continue to be an important method of inquiry in this field, but their merits are not uncontested, even among psychodynamic researchers (Fonagy, 2013). In modern psychotherapy research, case reports are recognized as providing weak evidence at best (Guyatt et al., 1995).

Historically, however, case reports can be viewed as attempts to align psychotherapy with the standards and practices of medicine (Wampold & Imel, 2015, p. 23). This tendency is also recognizable in early psychoanalytic theory, which provided a description of mental illness consistent with the medical model of disease: patients' symptoms are explicable by a common underlying cause (i.e., repressed trauma), which is targeted by specific therapeutic actions (e.g., free association; ibid., p. 18). Alignment with medicine thus secured an “ecological niche” for psychological therapy, turning it into a scientific, “civilized”, and generally trustworthy endeavor.

Psychotherapy research’s complex relationship with medicine is also reflected by its methodology. In the middle of the 20th century, researchers were increasingly involved in finding more objective ways to examine the effects of psychological treatment. A major development in this respect was the introduction of matched placebo controls, as suggested by Rosenthal & Frank (1956). The idea of comparing therapies to a “therapeutically inert” condition was adopted from medicine: implicitly, it conceptualizes psychotherapy as a medical treatment with a specific agent, the effect of which must be disentangled from unspecific or contextual factors.

“Psychological” and pill placebos are common comparators in psychotherapy studies until today, but their heuristic value remains contested (Kirsch et al., 2016).

Another major innovation was the adoption of randomized controlled trials (RCTs) in the field. This design had been introduced into medicine in the 1940s, based on a landmark double-blind study on streptomycin in pulmonary tuberculosis conceived by Austin Bradford Hill (1897-1991; Crofton, 2006), who himself drew on previous works by R. A. Fisher (Armitage, 2003). In his “Design of Experiments” (1935), Fisher had laid the foundations for modern experimental design, and explicated the statistical tools to draw inferences from them (Lehman, 2011). In the second half of the 20th century, RCTs also became popular in psychotherapy research (Basterfield & Lilienfeld, 2020).

RCTs are now the dominant design in psychotherapy research. The concept of “evidence-based medicine” (EBM) has contributed strongly to this development from the 1990s onwards, emphasizing the role of randomized trials to establish “evidence-supported treatments” (ESTs; Chambless & Hollon, 1998). Hundreds of RCTs have shown the efficacy of psychotherapies for various mental disorders since that time. This evidence was crucial in dispelling beliefs that psychological treatments were largely ineffective (Cuijpers, Karyotaki, et al., 2019), and in securing their place in various treatment guidelines.

Cognitive-behavioral treatments were among the first to be subjected to rigorous quantitative examination; for disorders like depression, their evidence-base now surpasses most other formats by orders of magnitude (Cuijpers, Miguel, Harrer, et al., 2023). Some see the development of ESTs as a more recent attempt to legitimize “psychological” therapies by treating them as a medical treatment, and by applying equivalent methods to study their effects (Wampold & Imel, 2015, p. 27). This innovation cycle reverted with the introduction of meta-analyses in medicine. We will return to this point later (see Article 1).

Randomized controlled evidence has been crucial to show that psychological treatment can be effective. However, other longstanding debates remain unsettled, the most notorious of which surrounds the “Dodo-Bird” verdict (“all have won, and all must have prizes”). Initially coined by Rosenzweig (1936) almost 90 years ago, this dictum refers to the fact that all bona fide therapies result in equivalent benefits, regardless of their therapeutic rationale.

This observation has often (but not always) been corroborated by modern effectiveness research, spawning recurrent discussions among scholars (Beutler, 2002; Budd & Hughes, 2009; Duncan, 2002; Luborsky et al., 2002; Stiles et al., 1986; Wampold et al., 1997). The Dodo-Bird retains its relevance due to the historic emphasis on specific, theory-driven “techniques” in most psychotherapeutic schools. Equivalent therapy outcomes could mean that therapeutic techniques do not target the underlying mechanism purported by their inventors: the developed rationale is in fact a “fiction”, and effects across all therapies emerge due to purely contextual factors (e.g., positive regard, expectations, remoralization). Following the medical model, these factors would be regarded as placebo effects.

While rejecting the term “placebo”, some theorists conceptualize psychotherapy along these lines. An early example is Frank & Frank’s (1993) “Persuasion & Healing”, originally published in 1961. This work develops the argument that psychotherapies work by providing patients with a coherent explanation for their symptoms (which need not be true), based on which salubrious activities are motivated.

More recently, Wampold (2001) drew on this tradition, developing of a “contextual model” of psychotherapy. This theory rejects “medical model”-type explanations of psychotherapy effects, emphasizing the social context in which psychotherapy occurs. All effective therapies are thought to operate through a common set of pathways: relationship and social belonging; creation of treatment expectations; and goal-oriented actions (Wampold & Imel, 2015, p. 53). This model is intuitively appealing, but cannot accommodate all empirical findings (Cuijpers, Reijnders, et al., 2019).

More recently, component network meta-analyses have unearthed several specific treatment components that may drive treatment effects, e.g. for affective disorders (Furukawa, Suganuma, et al., 2021; Furukawa et al., 2024; Miklowitz et al., 2021; Pompoli et al., 2018). Lastly, Wampold’s and others rejection of “the medical model” may also build up a straw man. In modern psychiatry, the biopsychosocial model of mental illness is almost universally accepted, as is the need for multimodal treatments. The latter are based on the understanding that there are multiple ways to conceptualize mental health problems (Huda, 2022).

Cuijpers, Reijnders & Huibers (2019) argue that current evidence is simply insufficient to conclude that psychotherapies work through specific techniques, common factors, or a combination of both. Cuijpers (2023) also argues that the “Dodo-Bird” debate itself may be misguided: given the dramatic treatment gap for mental disorders worldwide, it may be more relevant to determine what is “at least” needed to make psychological treatment effective, to ensure that interventions can be more efficiently disseminated.

This concludes our brief historical review. Tracing back the history of the field, we see that applications of “psychological” treatment were already firmly established by the turn of the 20th century, with precursors that reach back even further. What has changed, at times drastically, is how these cures where motivated, how individuals explained that their treatments work, and the methods to verify their effects.

Many of these redefinitions were shaped by broader scientific and societal trends at the time, and by developments in other disciplines (e.g., neurology, physiology, cognitive science). A guiding theme is psychotherapy’s connection with medicine, which continues to have a profound impact on the research methodology practiced in the field. Across these twists and turns, it remains open if psychotherapy research has indeed “progressed” as a science. This question will be examined in the following chapter.