Background and objectivesPsychiatric and clinical–psychological practice must be based on the finest scientific knowledge. In Spain, the corresponding disciplines are official specialisations in the health sciences. The present article aims documentally to scrutinise the involvement of science in the psychotherapeutic activity of both. MethodsA non-systematic study of quality scientific literature, mainly using the PubMed directory and Google Scholar, and examination of the applicable regulations. Results(1) Scientific method: Scientific knowledge is critical, well-founded, methodical, verifiable, and systematic. However, psychiatry and clinical psychology are hybrids of the natural and psychosocial sciences. (2) Psychotherapies and psychiatry: Psychiatry uses psychotherapies as well as various other authorised treatments. The Spanish Constitution and ministerial planning regulate the best training for health specialisations in Spain and guarantee the correct use of scientific knowledge. The US National Institute of Mental Health specifies that psychotherapies should be carried out by mental health professionals. (3) Psychotherapies and psychology: As specialised treatments, only psychiatry and clinical psychology have the optimal body of knowledge for practising psychotherapy. However, the plurality of psychological–psychotherapeutic schools is innumerable and not all of them are supported by science, although their efficacy seems to be similar. Other types of conversational interventions may accompany patients and, as they are not strictly speaking treatments, may be practised by people with a variety of qualifications or none at all. ConclusionsPsychotherapies are non-formal health interventions. Intrusiveness is common, to the detriment of the best scientific information.