We have demonstrated that between 1993 and 2005, there was overall a small change in the incidence of new diagnoses of depression and a small increase in the mean duration of the antidepressant prescription for the first episode of depression. However, there were more marked trends within age and sex, including a large rise in the incidence of new diagnoses among young women and, to a lesser extent, among young men.
The majority of antidepressant prescriptions were given as long term treatment or to patients with multiple episodes of depression. Small increases both in the proportion of patients in these groups and in the duration of prescriptions made to such individuals accounted for a near doubling of the total volume of antidepressant prescribing between 1993 and 2005. Although the proportion of new cases initially treated with antidepressants did rise slightly over this period, changes in recognition, case definition, or duration of initial prescription are unlikely to account for the dramatic increase in antidepressant prescribing. A key question remains: if the changes in antidepressant prescribing are accounted for by changes in the proportions of those in receipt of long term prescriptions, does this represent appropriate prescribing for those with chronic and relapsing disease according to current guidance or does it arise from a failure to discontinue antidepressants in those with milder illness, or both?
The majority of new episodes of depression were associated with antidepressant prescribing in the year of diagnosis (79%), similar to other studies.9 16 17
This proportion remained remarkably stable over the period studied, falling only in the last two years.
Strengths and limitations of study
The data on both diagnosis and prescribing in the GPRD are very reliable given the stability of the lists of registered patients and the healthcare system. The GPRD has no formal control on diagnostic categories though, which are determined by individual general practitioners. We did include all possible depression diagnostic codes in our study, but cannot exclude the possibility that some prescribing took place without any appropriate depression code. Also, prescribing records reflect the issue of prescriptions and not the dispensing or taking of the medication. Although the majority of prescribing takes place in primary care in the UK, medication may also be prescribed in other settings—for example, to hospital outpatients—but this is likely to contribute little overall in the UK.
In this study we were principally interested in patterns of prescribing rather than absolute numbers. Although the data are observational and we were unable to control for patient level confounders, we believe that this large dataset does give valuable insights into prescribing patterns in the UK. We can be less confident regarding the generalisability of our findings to other healthcare systems where antidepressant prescribing may not be so dominated by primary care physicians.
We restricted the analysis to practices that contributed data to the GPRD throughout the whole study period. We thought that although patients can leave individual practices, the stability provided by using the 170 stable practices would allow greater confidence in interpretation of trends within the data. Including all practices—some of which joined or left the database over the study period—would make trends in prescribing more difficult to interpret. The question arises as to whether the stable practices are representative of the whole practice population. Various factors reassure us that this is the case. Firstly, being a stable practice has no implications regarding the nature of the practice itself; the label just indicates that the practice was consistently contributing data that were regarded as up to standard for the entire study period. Secondly, there was no age or sex difference between the patients in the stable practices and those in the whole cohort, nor any major difference in diagnostic codes. We did identify that the incidence of depression appeared higher in the whole cohort. This disparity possibly arose as a result of incomplete data from some practices such that some cases of prevalent depression were included because of the absence of previous history codes.
Data that were entered into the GPRD system by general practitioners in the participating clinics were transferred to the GPRD organisation in batches. However, the decision on when to proceed with these transfers was made entirely by the clinics themselves. Hence, data collected close to the date on which we extracted data for this study, February 2006, might not contain the entire set from each clinic. This anomaly should only affect data from the final months of 2005 and is less likely to be a problem in the stable practices. We elected to include these data because a large number of observations were still available, and the incompleteness of the data should only have minimal effects on rates or proportions.
Comparison with other studies
Our data suggest that a small increase each year in the numbers of patients receiving repeat prescriptions accounts for a large increase in overall antidepressant prescribing volumes. Some support for these findings is found elsewhere in the literature.
In a Canadian study, the prevalence of new antidepressant prescriptions (defined in terms of no prescribing in the previous two years) rose between 1998 and 1999 then fell in 2004, whereas prescribing for prevalent cases doubled over the eight year study.16
These results are in accord with our findings and suggest that changes in the duration of prescribing are more important in determining overall prescription numbers than changes in the number of cases treated.
A US study similarly reported increased new prescribing of antidepressants to outpatients between 1987 and 1997, although no data were available on long term prescriptions.9
In another study, a cross section of general practitioner case notes was examined for patients on antidepressant prescriptions. The average duration of prescription was five to seven years where the prescribing indication was for mental health problems, suggesting that longer term prescribing dominates.9 11
Other previous studies have concentrated on the initial prescribing decision.17 18 19
National policy in the UK has focused on targeting antidepressants to patients with more severe symptoms by incentivising the use of questionnaire measures of severity before treatment through the UK general practice quality and outcomes framework.20
A recent study of prescribing patterns following initiation of the framework showed appropriate targeting of antidepressants.21
The proportion of patients with a new diagnosis prescribed an antidepressant (79%) was very similar to that in our study. This raises the question of how much influence the use of questionnaires actually has on the prescribing decision. It has already been established that patients are anxious regarding discontinuation of antidepressants and require support from their family doctor to stop medication.22
Patients not reviewed and supported are unlikely to initiate discontinuation on their own.
Long term prescribing is indicated for patients with recurrent or relapsing depression.23
Long term prescribing may, therefore, be appropriate and in line with current guidelines.15
The observed changes in antidepressant prescribing may represent better adherence to such guidelines. However, in one recent study involving detailed case review of patients on longer term antidepressant prescriptions, more than half of those examined (56%) failed to meet criteria for a formal psychiatric diagnosis.24
Independent case review showed that there was no indication for continued receipt of an antidepressant in nearly a third (31%) of participants.24
In another study of long term antidepressant prescribing, there was no documented mental health review over a two year period in 21% of the case notes.11
Antidepressant prescribing is much higher compared with 10 years ago. This increase is not because of an increase in the incidence of new cases of depression, a lower threshold for treatment, an increase in the proportion of new cases of depression for whom antidepressants are prescribed, or an increase in the duration of the prescriptions written for new cases of depression. Rather, the dramatic changes in antidepressant prescribing volumes between 1993 and 2005 seem to be largely because more patients are on long term medication and this group consumes the most drugs. In order to better understand the rise in antidepressant prescribing, research needs to focus on chronic prescribing and policy needs to focus on encouraging appropriate high quality monitoring and review of those patients who become established on long term prescriptions.
What is already known on this topic
- The United Kingdom, along with other Western countries, has seen a substantial increase in antidepressant prescribing over the past 20 years
- The reasons behind this rise are not well understood but do not seem to include lower thresholds for diagnosis or treatment, or changes in illness behaviour
What this study adds
- The incidence of new cases of depression between 1993 and 2005 rose in young women but fell slightly in other groups such that overall incidence declined slightly
- Long term prescribing accounts for the majority of antidepressant prescriptions
- The rise in antidepressant prescribing seems to be largely explained by a small increase in long term prescribing