Abstract Rationale: In therapeutic use, amitriptyline, reboxetine and citalopram have all been associated with apparent anticholinergic-like side effects (dry mouth, constipation, etc.), despite the very low antimuscarinic activity of reboxetine and citalopram in vitro. Objec- tives: We hypothesised that the spectral analysis of heart rate variability (HRV) might detect differences between amitriptyline, citalopram and reboxetine in their anticho- linergic activities following a single peroral administra- tion. Methods: In this double-blind, cross-over study, amitriptyline (75 mg), citalopram (20 mg), reboxetine (4 mg) and placebo were randomly given at 1-week in- tervals to eight healthy male volunteers. Drug and cate- cholamine concentrations in plasma were determined re- peatedly. The drug effect was assessed with periodic re- cordings of electrocardiogram (ECG) and blood pres- sure, and with measurements of salivary secretion. The ECG recordings were subjected to spectral analysis of HRV, in which the high frequency (HF) power of R–R interval (RRI) variability was supposed to reflect cardiac parasympathetic tone. Results: Reboxetine increased heart rate and blood pressure and reduced the HF power of RRI and 3,4-dihydroxyphenylglycol (DHPG) plasma concentrations. Amitriptyline diminished salivary secre- tion and had a prominent sedative action. Measurements after citalopram did not differ significantly from placebo. Conclusions: Reboxetine, despite its low antimuscarinic activity in vitro, had distinct effects on the HF power of RRI, consistent with anticholinergic activity in vivo. Amitriptyline had a measurable anticholinergic effect in the salivary glands, but, surprisingly, not in the heart. W suggest that the sedative effect of amitriptyline could a ter cardiac sympathovagal balance and, therefore, coun teract the anticholinergic drug effect. Keywords Amitriptyline · Citalopram · Reboxetine · Autonomic nervous system Introduction The present study was designed to investigate the cholinergic activity of amitriptyline, citalopram and boxetine, as representatives of three different grou antidepressive agents. Amitriptyline is a traditional tric clic antidepressant known to have a strong anticholiner gic effect in vitro (Richelson and Nelson 1984) and in v vo (Warrington et al. 1989). Citalopram is a selective se rotonin reuptake inhibitor (SSRI) which has less an muscarinic activity in vitro (Richelson and Nelson 1984), but, nevertheless, anticholinergic-like adverse e fects (dry mouth, constipation etc.) have been repo (Muldoon 1996). Reboxetine is a recently introduced se lective noradrenaline reuptake inhibitor (NARI) whi also has shown low affinity towards the muscarinic cho linergic receptors (Riva et al. 1989; Dostert et al. 1997) However, in therapeutic use, anticholinergic-like side e fects (dry mouth, urinary hesitancy or retention, et have also been reported for reboxetine (Berzewski et al 1997). In clinical trials, an anticholinergic drug effect is of- ten assessed by weighing the secreted saliva or by esti- mating the subjective dryness of mouth using visua analogy scales (VASs). Power spectral analysis of heart rate variability (HRV) offers another non-invasive meth od to quantify drug effects on autonomic nervous system activity (Pomeranz et al. 1985; Task Force 1996). high frequency (HF) component of HRV in particul which reflects respiratory sinus arrhythmia mediated b J. Penttilä · E. Syvälahti ( ✉ ) · H. Scheinin Department of Pharmacology and Clinical Pharmacology, University of Turku, Kiinamyllynkatu 10, 20520 Turku, Finland e-mail: erkka.syvalahti@utu.fi Fax: +35-8-23337216 S. Hinkka Department of Biostatistics, University of Turku, Turku, Finland T. Kuusela Department of Applied Mathematics, University of Turku, Turku, Finland H. Scheinin Turku PET Centre, Turku University Hospital, Turku, Finland Psychopharmacology (2001) 154:343–349 DOI 10.1007/s002130000664 O R I G I N A L I N V E S T I G AT I O N Jani Penttilä · Erkka Syvälahti · Susanna Hinkka Tom Kuusela · Harry Scheinin The effects of amitriptyline, citalopram and reboxetine on autonomic nervous system A randomised placebo-controlled study on healthy volunteers Received: 21 June 2000 / Accepted: 27 November 2000 / Published online: 17 February 2001 © Springer-Verlag 2001