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BackgroundSide effects play a key role in patients’ failure to take antidepressants. There is evidence that verbal suggestions and informed consent elicit expectations that can in turn trigger the occurrence of side effects. Prior experience or learning mechanisms are also assumed to contribute to the development of side effects, although their role has not been thoroughly investigated. In this study, we examined whether an antidepressant’s side effects can be learned via Pavlovian conditioning.MethodsParticipants (n = 39) were randomly allocated to one of two groups and were exposed to a classical conditioning procedure. During acquisition, 19 participants received amitriptyline and 20 participants received a placebo pill. Pills were taken for four nights together with a novel-tasting drink. After a washout phase, both groups received a placebo pill together with the novel-tasting drink (evocation). Side effects were assessed via the Generic Assessment of Side Effects Scale prior to acquisition (baseline), after acquisition, and after evocation. A score of antidepressant-specific side effects was calculated.ResultsParticipants taking amitriptyline reported significantly more antidepressant-specific side effects after acquisition compared to both baseline and the placebo group. After evocation, participants who underwent the conditioning procedure with amitriptyline reported significantly more antidepressant-specific side effects than those who never received amitriptyline, even though both groups received a placebo.ConclusionsOur results indicate that antidepressant side effects can be learned using a conditioning paradigm and evoked via a placebo pill when applied with the same contextual factors as the verum.

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Adverse events in clinical drug trials are often poorly assessed and reported. The absence of baseline assessment and structured symptom lists, as well as the fact that most drug trials are industry-sponsored are common sources of bias. In addition, adverse events are usually assessed in patient samples, which can bias results because of the misattribution of symptoms that are part of the illness to medication intake. We aimed to identify amitriptyline's placebo- and baseline-controlled side effects by examining a sample of healthy adults, using structured assessments via a symptom list. Forty healthy individuals were randomized equally to either a group taking 50 mg amitriptyline on four consecutive days or to a placebo control group. Complaints were assessed via the Generic Assessment of Side Effects Scale prior to and after four days of medication intake. Frequency of complaints and their intensity were compared after medication intake between the two groups while controlling for complaints at baseline. The amitriptyline group's participants reported having suffered from "dry mouth," "dizziness," "subjective blood circulation-associated problems," and "constipation" significantly more often. When taking into account the complaint's intensity, the amitriptyline group also reported higher intensities for "dry mouth," "dizziness," and "subjective blood circulation-associated problems." Our results emphasize the importance of a structured and well-controlled harm assessment. Future drug trials should report the placebo- and baseline-controlled side effects with a clear causal relationship to the intake of the drug under investigation, in addition to the frequency of complaints and their odds ratios. (PsycINFO Database Record