Drugs with anticholinergic properties are widely used. However, they may evoke a variety of adverse reactions (such as dry mouth and constipation, but also drowsiness and confusion), and therefore unnecessary use of drugs with anticholinergic properties should be avoided. In particular, older people are particularly vulnerable to the central anticholinergic effects of drugs. However, monitoring of drug-induced anticholinergic effects and drug concentrations in serum is challenging. In addition to the 'pure' anticholinergics such as atropine and oxybutynin, several other drugs whose principal mode of action is not anticholinergic, possess anticholinergic properties, thus increasing the risk of anticholinergic adverse effects. In this paper, we focus on the central anticholinergic effects of drugs, and on the usefulness of the serum anticholinergic assay (SAA) in the prediction of anticholinergic effects. Results on the anticholinergic effects of drugs on cognition are mixed. This may be because of differences in the populations as well as in the drugs used. In addition, the clinical conditions of the patients may affect the results. The SAA has been used in an attempt to measure anticholinergic burden. However, the results are variable and the SAA levels do not necessarily reflect the medication used by the patient. Therefore, its usefulness in determining anticholinergic adverse reactions is questionable.