Prescription sequence analysis (PSA) uses pharmacy‐based prescription drug histories to detect a subset of drug effects: those that are themselves indications for changes in the prescribing of another drug. Dutch pharmacy practice ensures virtually complete drug histories. With a database of 25,000 patients, we used PSA to test an alleged link between the use of the anti‐vertigo drug flunarizine and mental depression. The temporal sequence of anti‐depressant use among flunarizine users shows no clustering that would suggest a causal link. PSA can be run within a few days, which may make it helpful in resolving certain of the periodic controversies about adverse drug reactions.