Diet pill use is a significant problem in individuals with eating disorders in the clinic, yet few studies have investigated their use comprehensively. The objective of this study was to determine the prevalence of diet pill use and explore features associated with their use in a large, well-characterized sample of individuals with eating disorders.
We found the presence of diet pill use to be positively associated with other weight control behaviors (vomiting and other forms of purging), BMI, caffeine use, personality characteristics (trait anxiety, higher novelty seeking), and several Axis I and II disorders (any anxiety disorder, borderline personality disorder, alcohol abuse or dependence.)
Confirming our hypothesis, across eating disorder subtypes, significantly greater numbers of individuals in the PAN, BAN, PBN, and ANBN subtypes reported use of diet pills compared to individuals with RAN. Given that individuals with RAN are more likely to display high constraint characteristics than individuals with purging-type eating disorders (Casper, Hedeker, & McClough, 1992
) and by definition do not engage in binge eating or purging behaviors, a lower frequency of diet pill use in those with RAN was predicted.
Diet pill use was also associated positively with vomiting and other forms of purging. Although the relative rarity of use of diet pills as the sole weight control strategy in our sample was most likely an artifact of our inclusion and exclusion criteria, at least in this sample, diet pill use seems more typically to emerge as part of a constellation of weight control behaviors including purging behaviors rather than a solitary behavior. Moreover, as there was no significant relation between excessive exercise and diet pill use, diet pill use may best be conceptualized as clustered with other purging methods.
In terms of BMI, diet pill use was positively associated with current, highest and lowest lifetime BMI. However, odds ratios explain that the higher an individual’s BMI, the higher the odds of diet pill use, adjusting for age and eating disorder type. Given the strong association between diet pill use and highest maximum BMI, it is of note that diet pill use is more likely by individuals who are (or have been) normal weight or overweight than by those who are (or have been) underweight. This may suggest that diet pill use in not an effective weight loss strategy or means to keep weight down.
Diet pill use was also associated positively with increased novelty seeking, borderline personality disorder, and alcohol abuse or dependence. This association may support the existence of an eating disorder subgroup that exhibits a cluster of impulsive, problematic behaviors. Previously described as “multi-impulsive,” these individuals with BN have been found to display poor response to treatment (Fichter, Quadflieg, & Rief, 1994
) as well as other negative outcomes (Keel & Mitchell, 1997
; Myers et al., 2006
). The identification of diet pill use as another behavior that may characterize these individuals is important for further understanding the nature of eating pathology in this particularly severe subgroup of eating disorder patients.
Interestingly, the same pattern of findings did not hold for narcissistic personality disorder. Although not significant at our alpha level of 0.01, a trend-level difference emerged (p < 0.02) which was in the opposite direction of that observed for novelty seeking, borderline personality disorder, and alcohol abuse or dependence. Although this could be a chance finding, the fact that narcissistic personality disorder was associated with less diet pill use is intriguing and cautions against assuming that all cluster B personality disorders are similarly associated with diet pill usage.
Diet pill use was also associated with trait anxiety and anxiety disorders. Previous studies have shown that individuals with eating disorders who are impulsive also exhibit anxious traits (Cassin & von Ranson, 2005
; Fichter et al., 1994
). Within these populations, diet pill use together with the constellation of other substances and problematic behaviors may be impulsively driven responses to underlying anxiety about body weight and weight gain.
It is noteworthy that diet pill use was not associated with major depression. This finding was contrary to our hypothesis but may be due to the fact that of the 916 individuals in the sample with major depressive disorder, 22% had a RAN diagnosis, and 29% had an ANBN diagnosis. Thus, the lack of an association between diet pill use and depression may be due to the fact that the highest frequencies of depression were in those who gravitated towards other weight control behaviors (e.g., excessive exercise.)
This study has the following limitations of note. The cross-sectional design necessitated retrospective reports which are susceptible to recall bias. Moreover, it is possible that our assessment of diet pill use may underestimate frequency of use. Self-report assessment has been shown to underestimate laxative use as compared to urine screening in individuals with AN (Turner, Batik, Palmer, Forbes, & McDermott, 2000
). Further, in this study, diet pill use was assessed by interview and it is unknown whether structured interview reports are superior to self-report of diet pill use. Moreover, variability in our measurement of current and worst diet pill use, and diet pill brands, limited our focus to lifetime diet pill use. Finally, because part of the study sample (BN-ARP study) was collected for linkage analysis, targeting families with multiple affected individuals, ascertainment bias must be considered. Thusly, selection through multiple affected individuals may have led to over sampling of families containing multiple type-specific genes. In turn, affected individuals who come from high density families may differ systematically from sporadic cases in ways we are unable to ascertain.
In conclusion, diet pill use in individuals with eating disorders is associated with vomiting and other purging behavior, BMI, caffeine use, novelty seeking, trait anxiety, and other Axis I and II disorders (any anxiety disorder, borderline personality disorder, alcohol abuse or dependence,). Given the observed frequency of diet pill use in individuals with eating disorders, the unregulated nature of these substances, and the ease with which they can be obtained, assessment of diet pill use—including brand, source, and dosage, should be routine.