Because the age, sex and treatment continuation distributions of the alprazolam and lorazepam patients are similar, differences observed in rates of events are unlikely to be due to these characteristics. However, it should be remembered that the reasons for the benzodiazepines being prescribed were not identified and may be differently distributed among the two groups. The possibility that any medical event recorded after starting treatment is also a pre-existing condition should be borne in mind when considering the results of this study, as should the fact that an ‘event’ is not necessarily an ADR.

The most common adverse effect of benzodiazepines is central nervous system depression, although the specific manifestations depend on the particular drug and on the sensitivity of the individual patient . The most frequently reported symptoms are drowsiness, depression, impaired intellectual function and memory, lethargy and impaired coordination. Other common adverse effects are dizziness or lightheadedness, headache, nausea or vomiting and other gastrointestinal symptoms, skin rash, and respiratory disturbances and infections. In our study, sleep , depressive disorder, dizziness or vertigo, respiratory symptoms, esophagus and stomach disorders, and inflammatory skin conditions occurred significantly more often in the first period after starting both drugs (Tables 1,2). Sleep disorders and dizziness or vertigo occurred more often after starting treatment with either drug in both sexes and dizziness or vertigo occurred more often at all ages in the lorazepam patients and in elderly alprazolam patients.