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The cost of tranquilizers
0277-9536/82!221955-04$03.OQKt Pergamon Press Ltd
Sot. Sci. Med. Vol. 16. pp. 1955 to 1958. 1982 Printed m Great Britain
THE
COST
OF TRANQUILIZERS PAUL WILLIAMS
General Practice Research Unit, Institute of Psychiatry, de Crespigny Park, London SE5. England
The last two decades have seen large increases in the number of psychotropic drugs that are prescribed and dispensed each year [l-3]. This phenomenon has given rise to much concern and criticism, on at least three grounds [4]. First, psychotropic prescribing is criticised on clinica/ groutids: it is said that many of the prescriptions are unnecessary [2,5]. although this view is not always substantiated [6], and attention is drawn to their dependence-producing properties [7.8] as well as to other undesirable consequences [9]. Second, psychotropic prescribing is criticised on moral grounds: in Parry et a/.‘~ view, if “man takes tranquilisers in order to withdraw from universal difficulties which man is born to cope with, this undermines social character” [lo]. Others see a political dimension. and regard psychotropic drug use as a form of exploitation [ 11. 121. Third, psychotropic use is criticised on jinancial grounds. Attention is drawn to the cost of such drugs [Z, 131, usually with the implication that the money at present spent on tranquilizers and other psychotropics would be better spent somehow else. In 1979, a joint statement by the Secretary of State for Social Services and the Secretary of the British Medical Association expressed anxiety on the part of the Department and the profession about the cost of drugs. especially those whose prescription was greatly affected by patient demand. They initiated a campaign aimed at persuading patients to “leave the doctor empty-handed” (i.e. without a prescription). This paper examines trends in the overall cost of tranquilizers in England during the years 1966-1977 [14]. and constructs a model to describe and explain these changes.
TRENDS
IN DRUG
COST
The Department of Health and Social Security publishes annual figures for the cost of various categories of drug [ 151. These are based on data collected by the Prescription Pricing Authority. and are from prescriptions dispensed in retail pharmacies. Hospital pharmacies are not included, so that the data are derived. in the main, from prescriptions written by G.P.s. The figures are given as toral rlet,ingredient cosr (TNICt-i.e. the total cost of the drugs themselves, excluding the cost of packaging and dispensing. Figure 1 shows the TNIC for tranquilizers dispensed in England during the years 1966-1977. It can be seen that for the years 19661972. there was a virtually linear increase (about LO.8 million per year). A sharp drop in TNIC occurred in 1973 and 1974. but there was a steep increase thereafter. The TNIC for 1977. f17.8 million. \vas more than three times the 1966 figure of 0.5 million. and the total ‘bill’ for tran-
quilizers lion.
across
the 12 year period
A MODEL
FOR
DRUG
was fl15.07
mil-
COST
The TNIC of any group of drugs is the product of the number of prescriptions dispensed and the mean cost of each prescription. The cost of each prescription is itself the product of the amount of drug dispensed, and the unit cost of the drug (e.g. in pence per mg.). Thus, TNIC can be modelled as follows: log TNIC
= m + h, log n +h~logu+bJlOgc+e(l)
where n is the number of prescriptions, a the average amount of drug per prescription and c the unit cost. m, ht, b, and h3 are constants and e is an error term, the amount by which log TNIC predicted by the model differs from the observed value. Information about the number of prescriptions is published annually by the DHSS. There is, however, no direct information about the unit cost of tranquilizers. Since there are a large number of such drugs, each with a different price, and prescribed in different quantities, an average unit cost of tranquilizers would be virtually impossible to calculate, so that it must be represented by an approximation. It will be represented by the Index of Wholesale Prices of Pharmaceutical Preparations (IWPP), published annually by the Department of Trade [16]. For the 1972-1977 data, a further term has to be entered into the model. The Monopolies Commission, in a report published in 1973 [17], ordered a substantial reduction in the cost of chlordiazepoxide and diazepam. Since these two drugs account for a substantial proportion of tranquilizer prescriptions, this must be allowed for in the model. There are a variety of preparations of these two drugs, packaged in different quantities and sold at different prices. Thus, their unit cost must again be represented by an approximation. The price (in pence) of a 500 tablet pack of 5 mg Valium (Roche) was chosen, since this preparation is the most comfionly prescribed, and this package the most commonly sold to the NHS. Since this price changed rapidly in 1972 and 1973, a weighted average price for each year has been calculated. There is no information at all on trends in the average amount of drug per prescription, nor any way of approximating it. For the time being, therefore, this must be dropped from the model. So. for the 1966-1971 data. the model is
1955
log TNIC
= n1 + b, log II + b, log IWPP
+ el
(2)
PAUL WILLIAMS
1956
----
Observed Predicted
I
I
I
I
I
I
I
I
I
I
I
I
66
67
68
69
70
71
72
73
74
75
76
77
Years
Fig. I. The cost of tranquilizers dispensed at retail pharmacies in England. 1966-1977. and for the years 1972-1977 log TNIC
= m + b, log n + b3 log IWPP
+ b4 Val + e,
(3)
where Val is the weighted average annual price of Valium, as described above, and e, = (e + b2 log a), i.e. the effect of the average amount of drug per prescription has been (for the time being) relegated to the error term. These two models were then fitted to the data by the least squares method, and the goodness of fit assessed by analysis of variance. RESULTS
The data are shown in Table 1, and the results of the two analyses in Tables 2 and 3. The model fitted
to the 1966-1971 data accounted for nearly 99% of the variance, and yielded an F ratio of 116.42 (d.f. 2,3. P < O.OO@l).The residuals were uncorrelated (DurbinWatson d = 2.12, NS) and the standard error of estimate was 0.028 (0.32% of the mean log, TNIC value). The values of TNIC predicted by the model are shown in Fig. 1: the largest residual was f231,000, for 1968, an error amounting to 2.72% of the observed figure. It can be seen from Table 2 that compared with the effect of log,n, that log, IWPP was relatively unimportant. On its own, log,IWPP accounted only for 39% of the variance in log,TNIC (although this was statistically significant), compared with 98% accounted for by log,n on its own. Similarly, the stancoefficient for logcn was dardized regression
Table 1. Data for the models
Year 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977
Tranquilizers dispensed at retail pharmacies in England TNIC (fOO0) No. (000s) 5507 6615 7644 8482 9150 10.229 10.730 8741 8144 9494 13.558 17.773
.
11.687 13,605 14,863 15,370 16.039 17.062 18,143 19,149 20,083 20,540 21.190 20.836
*Scaled such that the 1966 value = 100.
Index oPL wholesale prices of pharmaceutical preparations
Weighted average annual cost of 500 x 5 mg Valium
loo.0 99.0 99.7 99.0 100.9 105.5
I1 I.1 114.4 129.2 163.6 196.0 226.9
391 181 123 I28 367 542
The cost of tranquilizers
1957
Table 2. Analysis of tranquilizer cost 1966-1971 Source log,n + log, IWPP 1 log, n only Addition of log, IWPP log, IWPP only { Addition of log, n Residual Total
hv log,IWPP Constant
SSq
o/0var
0.25146 0.24995 0.00151 0.09900 0.15246 0.00323 0.25469
98.73 98.14 0.59 38.87 59.86 1.27
(11 (11 (11 3 5
100
Regression coefficient
Standard error
1.57356 0.87478 - 10.17098
0.09450 0.52791 -
0.938 f 0.094, compared with 0.093 + 0.528 for log,IWPP. Table 3 shows the analysis for the second block of six years, 1972-1977. The model accounted for more than 99% of the variance, and yielded an F ratio of 233.66 (d.f. 3, 2, P < 0.0001). The residuals were again uncorrelated (Durbin-Watson d = 2.38 NS), and the standard error of estimate was 0.018 (0.18% of the mean log,TNIC value). The values of TNIC predicted by the model are shown in Fig. 1. The largest residual
was f304,000, for 1977, an error amounting to 1.71% of the observed value. It can be seen from Table 3 that the effect of log,n was relatively insignificant when compared with the joint effect of the two cost variables. Between them, log,TNIC and log,Val accounted for 99.25% of the variance in log,TNIC: on its own, log,n accounted for only 20.19%. DISCUSSION
Despite the small number of data points in each analysis, the models fitted well. The regression coefficients were. with one exception (that of IWPP in the
MSq
F
0.12573
116.42
0.00151 0.24995 0.09900 0.15246 0.00108
1.40> 231.44 91.67 141.17 -
d.f.
Standardized regression coefficient 0.93789 0.09333 -
first model) satisfactorily precise. However, before any model can be said to fit, it must be shown that successive pairs of residuals are independent. If they are not (a phenomenon *known as autocorrelation [IS]), then the presence of a non-random component in the residuals is implied. In the present context this is not merely an abstruse statistical consideration. Earlier, the effect of log,a (amount of drug per prescription) was put into the error term. If changes in log,a have exerted a significant effect on log TNIC, then successive error terms (i.e. residuals) will not be independent, and autocorrelation will be found to be present. Neither of the models displayed a significant autocorrelation effect, so such changes as these may have been in the amount of tranquilizer per prescription have not contributed significantly to changes in the total cost of tranquilizers. During 1966-1971, the price of tranquilizers was relatively stable, and changes in the total cost were found to be due almost entirely to increases in prescribing. During 1972-1977, the price of tranquilizers was subject to large changes, for two reasons. Firstly, inflation, represented here by the index of wholesale prices of pharmaceutical preparations, and secondly,
Table 3. Analysis of tranquilizer cost 1972-1977 Source log,n + log,IWPP + log,Val log,IWPP + log, Val { addition of log,rt log,r7 1 addition of log,IWPP + log, Val
Total
loge!7 log,IWPP log,Val Constant
SSq
y0 var
d.f.
Msq
F
0.438 13 0.43607 0.00205 0.08869 0.34944 0.29153 0.34129 0.00125 0.43938
99.72 99.25 0.47 20.19 79.53 66.35 77.67 0.28 100
t:, (1) (1) (2) (1) (1)
0.14604 0.21804 0.00205 0.08869 0.17472 0.29153 0.34129 O.ooO63 -
233.66 348.86 3.28 141.90 279.55 466.45 546.06
2 5
Regression coefficient
Standard error
Standardized regression coefficient
- 1.40490 0.82662 0.23989 17.74496
0.13515 0.02678 0.01250 -
-0.27728 0.82325 0.51 189 -
P.AL’L
1958
a reduction in the price of diazepam and chlordiazepoxide as a result of the Monopolies Commission enquiry. These changes had a dramatic effect on the total cost of tranquilizers. to the extent that the effect of variations in prescribing became negligible. Indeed. it can be calculated that if the same number of prescriptions had been dispensed each year between 1972 and 1977-i.e. no increase at all in prescribing--then the total tranquilizer bill for those six years (the sum of the TNICs) would have been f65.25 million, 950/, of the actual figure of E68.17 million. The findings suggest that any debate on drug cost should acknowledge the effect of pharmaceutical industry pricing policy and that of inflation. as well as considering the prescribing behaviour of doctors. It is likely. however, that as the inflation rate falls (and in the absence of large, externally imposed changes in the price of benzodiazepines) that the extent of prescribing will again become a more important determinant of total cost: i.e. the first model, rather than the second, will probably apply tb the data from the early 1980’s when they become available. Acknowledgements-Thanks are due to Professor Michael Shepherd. Dr Anthony Glare and Dr Graham Dunn, who advised and commented on earlier versions of this paper. The study was conducted while the author was funded by the Department of Health and Social Security, but the views expressed in this paper do not necessarily represent the views of the Department. Thanks are also due to Roche Products Ltd for supplying information about the cost of Valium.
REFERENCES 1. Parish P. A. The prescribing of psychotropic general practice. JI R. Co/l. Gen. Pratt. 21, l-77, 1971.
drugs SUPPI.
in 4,
WILLIAMS
1. Trethowan W. H. Pills for personal problems. Br. reed. J. 3. 749-751. 1975. of psycho3. Williams P. Recent trends in the prescribing tropic drugs. He&t/~ Trrr~ds 12. 6-7. 1980. 4. Williams P. and Glare A. W. Psychosocial Disorders if1 Gnlrral Practice. Academic Press. London. 1979. drugs. 5. Dunlop D. The use and abuse of psychotropic Proc. R. Sot. .Lled. 63. 1279-1X?. 1970. 6. Editorial: stress. distress and drug treatment. L~~crt 4. 1347-1348, 1978. 7. Lader M. H. Deper~dertcr 011 Prrscrihed Ps~chot,opi~ Drugs. Smith. Kline & French Publications. Welwyn Garden City, 1980. H. and Lader M. H. Benzodiazepine depen8. Petursson dence. Br. J. Addict. 76. 133-145. 1981. 9. Skegg D. C. G., Richards S. M. and Doll R. Minor tranquilizers and road accidents. Br. 4fed. J. I. 917-919. 1979. IO. Parry H. J.. Balter M. B.. Mellinger G. D.. Cisin I. H. and Manheimer D. I. National patterns of psychotherapeutic drug use. Arc/u yen. Ps.whiur. 28, 769-783. 1973. I I. Stoessel J. Psychopharrnika-dir rrrordurte .4r1passw~~. Piper. Munich. 1973. 12. Waldron I. Increased prescribing of Valium. Librium and other drugs. Itlt. J. H/t/t k-r. I. 37-62. 1977. 13. Tyrer P. Drug treatment of psychiatric patients in general practice. Br. Med. J. 2. 1008-1010. 1978. 14. 1977 is the latest year for which data have been published. 15. Published annually in Hrdth and Prrsorwl Sock/ Services Statistics. Her Majesty’s Stationery Office. London. 16. Published annually in Cerrtrcti Statistical Office ,4w1utr/ Abstract of Statistics. Her Majesty’s Stationary Office. London. 17. Monopolies Commission. A Report on the Supply of Chlordiazepolride and Dia-_eoam. Her Maiestv’s Stahonery Office, London. 18. Ostrom C. W. Time Series Analysis. Sage. Beverely Hills.
Sot. Sci. Med. Vol. 16. pp. 1955 to 1958. 1982 Printed m Great Britain
THE
COST
OF TRANQUILIZERS PAUL WILLIAMS
General Practice Research Unit, Institute of Psychiatry, de Crespigny Park, London SE5. England
The last two decades have seen large increases in the number of psychotropic drugs that are prescribed and dispensed each year [l-3]. This phenomenon has given rise to much concern and criticism, on at least three grounds [4]. First, psychotropic prescribing is criticised on clinica/ groutids: it is said that many of the prescriptions are unnecessary [2,5]. although this view is not always substantiated [6], and attention is drawn to their dependence-producing properties [7.8] as well as to other undesirable consequences [9]. Second, psychotropic prescribing is criticised on moral grounds: in Parry et a/.‘~ view, if “man takes tranquilisers in order to withdraw from universal difficulties which man is born to cope with, this undermines social character” [lo]. Others see a political dimension. and regard psychotropic drug use as a form of exploitation [ 11. 121. Third, psychotropic use is criticised on jinancial grounds. Attention is drawn to the cost of such drugs [Z, 131, usually with the implication that the money at present spent on tranquilizers and other psychotropics would be better spent somehow else. In 1979, a joint statement by the Secretary of State for Social Services and the Secretary of the British Medical Association expressed anxiety on the part of the Department and the profession about the cost of drugs. especially those whose prescription was greatly affected by patient demand. They initiated a campaign aimed at persuading patients to “leave the doctor empty-handed” (i.e. without a prescription). This paper examines trends in the overall cost of tranquilizers in England during the years 1966-1977 [14]. and constructs a model to describe and explain these changes.
TRENDS
IN DRUG
COST
The Department of Health and Social Security publishes annual figures for the cost of various categories of drug [ 151. These are based on data collected by the Prescription Pricing Authority. and are from prescriptions dispensed in retail pharmacies. Hospital pharmacies are not included, so that the data are derived. in the main, from prescriptions written by G.P.s. The figures are given as toral rlet,ingredient cosr (TNICt-i.e. the total cost of the drugs themselves, excluding the cost of packaging and dispensing. Figure 1 shows the TNIC for tranquilizers dispensed in England during the years 1966-1977. It can be seen that for the years 19661972. there was a virtually linear increase (about LO.8 million per year). A sharp drop in TNIC occurred in 1973 and 1974. but there was a steep increase thereafter. The TNIC for 1977. f17.8 million. \vas more than three times the 1966 figure of 0.5 million. and the total ‘bill’ for tran-
quilizers lion.
across
the 12 year period
A MODEL
FOR
DRUG
was fl15.07
mil-
COST
The TNIC of any group of drugs is the product of the number of prescriptions dispensed and the mean cost of each prescription. The cost of each prescription is itself the product of the amount of drug dispensed, and the unit cost of the drug (e.g. in pence per mg.). Thus, TNIC can be modelled as follows: log TNIC
= m + h, log n +h~logu+bJlOgc+e(l)
where n is the number of prescriptions, a the average amount of drug per prescription and c the unit cost. m, ht, b, and h3 are constants and e is an error term, the amount by which log TNIC predicted by the model differs from the observed value. Information about the number of prescriptions is published annually by the DHSS. There is, however, no direct information about the unit cost of tranquilizers. Since there are a large number of such drugs, each with a different price, and prescribed in different quantities, an average unit cost of tranquilizers would be virtually impossible to calculate, so that it must be represented by an approximation. It will be represented by the Index of Wholesale Prices of Pharmaceutical Preparations (IWPP), published annually by the Department of Trade [16]. For the 1972-1977 data, a further term has to be entered into the model. The Monopolies Commission, in a report published in 1973 [17], ordered a substantial reduction in the cost of chlordiazepoxide and diazepam. Since these two drugs account for a substantial proportion of tranquilizer prescriptions, this must be allowed for in the model. There are a variety of preparations of these two drugs, packaged in different quantities and sold at different prices. Thus, their unit cost must again be represented by an approximation. The price (in pence) of a 500 tablet pack of 5 mg Valium (Roche) was chosen, since this preparation is the most comfionly prescribed, and this package the most commonly sold to the NHS. Since this price changed rapidly in 1972 and 1973, a weighted average price for each year has been calculated. There is no information at all on trends in the average amount of drug per prescription, nor any way of approximating it. For the time being, therefore, this must be dropped from the model. So. for the 1966-1971 data. the model is
1955
log TNIC
= n1 + b, log II + b, log IWPP
+ el
(2)
PAUL WILLIAMS
1956
----
Observed Predicted
I
I
I
I
I
I
I
I
I
I
I
I
66
67
68
69
70
71
72
73
74
75
76
77
Years
Fig. I. The cost of tranquilizers dispensed at retail pharmacies in England. 1966-1977. and for the years 1972-1977 log TNIC
= m + b, log n + b3 log IWPP
+ b4 Val + e,
(3)
where Val is the weighted average annual price of Valium, as described above, and e, = (e + b2 log a), i.e. the effect of the average amount of drug per prescription has been (for the time being) relegated to the error term. These two models were then fitted to the data by the least squares method, and the goodness of fit assessed by analysis of variance. RESULTS
The data are shown in Table 1, and the results of the two analyses in Tables 2 and 3. The model fitted
to the 1966-1971 data accounted for nearly 99% of the variance, and yielded an F ratio of 116.42 (d.f. 2,3. P < O.OO@l).The residuals were uncorrelated (DurbinWatson d = 2.12, NS) and the standard error of estimate was 0.028 (0.32% of the mean log, TNIC value). The values of TNIC predicted by the model are shown in Fig. 1: the largest residual was f231,000, for 1968, an error amounting to 2.72% of the observed figure. It can be seen from Table 2 that compared with the effect of log,n, that log, IWPP was relatively unimportant. On its own, log,IWPP accounted only for 39% of the variance in log,TNIC (although this was statistically significant), compared with 98% accounted for by log,n on its own. Similarly, the stancoefficient for logcn was dardized regression
Table 1. Data for the models
Year 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977
Tranquilizers dispensed at retail pharmacies in England TNIC (fOO0) No. (000s) 5507 6615 7644 8482 9150 10.229 10.730 8741 8144 9494 13.558 17.773
.
11.687 13,605 14,863 15,370 16.039 17.062 18,143 19,149 20,083 20,540 21.190 20.836
*Scaled such that the 1966 value = 100.
Index oPL wholesale prices of pharmaceutical preparations
Weighted average annual cost of 500 x 5 mg Valium
loo.0 99.0 99.7 99.0 100.9 105.5
I1 I.1 114.4 129.2 163.6 196.0 226.9
391 181 123 I28 367 542
The cost of tranquilizers
1957
Table 2. Analysis of tranquilizer cost 1966-1971 Source log,n + log, IWPP 1 log, n only Addition of log, IWPP log, IWPP only { Addition of log, n Residual Total
hv log,IWPP Constant
SSq
o/0var
0.25146 0.24995 0.00151 0.09900 0.15246 0.00323 0.25469
98.73 98.14 0.59 38.87 59.86 1.27
(11 (11 (11 3 5
100
Regression coefficient
Standard error
1.57356 0.87478 - 10.17098
0.09450 0.52791 -
0.938 f 0.094, compared with 0.093 + 0.528 for log,IWPP. Table 3 shows the analysis for the second block of six years, 1972-1977. The model accounted for more than 99% of the variance, and yielded an F ratio of 233.66 (d.f. 3, 2, P < 0.0001). The residuals were again uncorrelated (Durbin-Watson d = 2.38 NS), and the standard error of estimate was 0.018 (0.18% of the mean log,TNIC value). The values of TNIC predicted by the model are shown in Fig. 1. The largest residual
was f304,000, for 1977, an error amounting to 1.71% of the observed value. It can be seen from Table 3 that the effect of log,n was relatively insignificant when compared with the joint effect of the two cost variables. Between them, log,TNIC and log,Val accounted for 99.25% of the variance in log,TNIC: on its own, log,n accounted for only 20.19%. DISCUSSION
Despite the small number of data points in each analysis, the models fitted well. The regression coefficients were. with one exception (that of IWPP in the
MSq
F
0.12573
116.42
0.00151 0.24995 0.09900 0.15246 0.00108
1.40> 231.44 91.67 141.17 -
d.f.
Standardized regression coefficient 0.93789 0.09333 -
first model) satisfactorily precise. However, before any model can be said to fit, it must be shown that successive pairs of residuals are independent. If they are not (a phenomenon *known as autocorrelation [IS]), then the presence of a non-random component in the residuals is implied. In the present context this is not merely an abstruse statistical consideration. Earlier, the effect of log,a (amount of drug per prescription) was put into the error term. If changes in log,a have exerted a significant effect on log TNIC, then successive error terms (i.e. residuals) will not be independent, and autocorrelation will be found to be present. Neither of the models displayed a significant autocorrelation effect, so such changes as these may have been in the amount of tranquilizer per prescription have not contributed significantly to changes in the total cost of tranquilizers. During 1966-1971, the price of tranquilizers was relatively stable, and changes in the total cost were found to be due almost entirely to increases in prescribing. During 1972-1977, the price of tranquilizers was subject to large changes, for two reasons. Firstly, inflation, represented here by the index of wholesale prices of pharmaceutical preparations, and secondly,
Table 3. Analysis of tranquilizer cost 1972-1977 Source log,n + log,IWPP + log,Val log,IWPP + log, Val { addition of log,rt log,r7 1 addition of log,IWPP + log, Val
Total
loge!7 log,IWPP log,Val Constant
SSq
y0 var
d.f.
Msq
F
0.438 13 0.43607 0.00205 0.08869 0.34944 0.29153 0.34129 0.00125 0.43938
99.72 99.25 0.47 20.19 79.53 66.35 77.67 0.28 100
t:, (1) (1) (2) (1) (1)
0.14604 0.21804 0.00205 0.08869 0.17472 0.29153 0.34129 O.ooO63 -
233.66 348.86 3.28 141.90 279.55 466.45 546.06
2 5
Regression coefficient
Standard error
Standardized regression coefficient
- 1.40490 0.82662 0.23989 17.74496
0.13515 0.02678 0.01250 -
-0.27728 0.82325 0.51 189 -
P.AL’L
1958
a reduction in the price of diazepam and chlordiazepoxide as a result of the Monopolies Commission enquiry. These changes had a dramatic effect on the total cost of tranquilizers. to the extent that the effect of variations in prescribing became negligible. Indeed. it can be calculated that if the same number of prescriptions had been dispensed each year between 1972 and 1977-i.e. no increase at all in prescribing--then the total tranquilizer bill for those six years (the sum of the TNICs) would have been f65.25 million, 950/, of the actual figure of E68.17 million. The findings suggest that any debate on drug cost should acknowledge the effect of pharmaceutical industry pricing policy and that of inflation. as well as considering the prescribing behaviour of doctors. It is likely. however, that as the inflation rate falls (and in the absence of large, externally imposed changes in the price of benzodiazepines) that the extent of prescribing will again become a more important determinant of total cost: i.e. the first model, rather than the second, will probably apply tb the data from the early 1980’s when they become available. Acknowledgements-Thanks are due to Professor Michael Shepherd. Dr Anthony Glare and Dr Graham Dunn, who advised and commented on earlier versions of this paper. The study was conducted while the author was funded by the Department of Health and Social Security, but the views expressed in this paper do not necessarily represent the views of the Department. Thanks are also due to Roche Products Ltd for supplying information about the cost of Valium.
REFERENCES 1. Parish P. A. The prescribing of psychotropic general practice. JI R. Co/l. Gen. Pratt. 21, l-77, 1971.
drugs SUPPI.
in 4,
WILLIAMS
1. Trethowan W. H. Pills for personal problems. Br. reed. J. 3. 749-751. 1975. of psycho3. Williams P. Recent trends in the prescribing tropic drugs. He&t/~ Trrr~ds 12. 6-7. 1980. 4. Williams P. and Glare A. W. Psychosocial Disorders if1 Gnlrral Practice. Academic Press. London. 1979. drugs. 5. Dunlop D. The use and abuse of psychotropic Proc. R. Sot. .Lled. 63. 1279-1X?. 1970. 6. Editorial: stress. distress and drug treatment. L~~crt 4. 1347-1348, 1978. 7. Lader M. H. Deper~dertcr 011 Prrscrihed Ps~chot,opi~ Drugs. Smith. Kline & French Publications. Welwyn Garden City, 1980. H. and Lader M. H. Benzodiazepine depen8. Petursson dence. Br. J. Addict. 76. 133-145. 1981. 9. Skegg D. C. G., Richards S. M. and Doll R. Minor tranquilizers and road accidents. Br. 4fed. J. I. 917-919. 1979. IO. Parry H. J.. Balter M. B.. Mellinger G. D.. Cisin I. H. and Manheimer D. I. National patterns of psychotherapeutic drug use. Arc/u yen. Ps.whiur. 28, 769-783. 1973. I I. Stoessel J. Psychopharrnika-dir rrrordurte .4r1passw~~. Piper. Munich. 1973. 12. Waldron I. Increased prescribing of Valium. Librium and other drugs. Itlt. J. H/t/t k-r. I. 37-62. 1977. 13. Tyrer P. Drug treatment of psychiatric patients in general practice. Br. Med. J. 2. 1008-1010. 1978. 14. 1977 is the latest year for which data have been published. 15. Published annually in Hrdth and Prrsorwl Sock/ Services Statistics. Her Majesty’s Stationery Office. London. 16. Published annually in Cerrtrcti Statistical Office ,4w1utr/ Abstract of Statistics. Her Majesty’s Stationary Office. London. 17. Monopolies Commission. A Report on the Supply of Chlordiazepolride and Dia-_eoam. Her Maiestv’s Stahonery Office, London. 18. Ostrom C. W. Time Series Analysis. Sage. Beverely Hills.