Original Article

International Journal of Obesity (2014) 38, 292–298; doi:10.1038/ijo.2013.74; published online 11 June 2013

Addiction potential of phentermine prescribed during long-term treatment of obesity

E J Hendricks1, M Srisurapanont2, S L Schmidt3, M Haggard1, S Souter1, C L Mitchell1, D G De Marco1, M J Hendricks1, Y Istratiy1 and F L Greenway4

  1. 1Center for Weight Management, Roseville, CA, USA
  2. 2Department of Psychiatry, Chiang Mai University, Chiang Mai, Thailand
  3. 3Department of Endocrinology, Metabolism & Diabetes, University of Colorado, Anschutz Medical Campus, Aurora, CO, USA
  4. 4Pennington Biomedical Research Center of the Louisiana State University System, Baton Rouge, LA, USA

Correspondence: Dr EJ Hendricks, Center for Weight Management, 2510 Douglas Boulevard, Suite 200, Roseville, CA 95661, USA. E-mail: edhendricks@surewest.net

Received 11 February 2013; Revised 7 April 2013; Accepted 10 April 2013
Accepted article preview online 17 May 2013; Advance online publication 11 June 2013

Editor's Note:

Phentermine was approved by the US FDA in 1959 for short term use for obesity. It is the most commonly used anti-obesity drug on the US market and many US bariatric physicians use phentermine long term, ignoring the FDA guidelines that it be used for three months or less. Phentermine is not approved for use in Europe and some other countries around the world because of the fear of addiction, tachycardia, and elevated blood pressure. Actual objective assessments of phentermine, as compared to administrative opinions, have been rare. The article by Hendricks et al in this issue is one of the few available in the literature. The study is not optimally designed, but suggests that fears of addiction to phentermine are exaggerated. None of the 269 subjects who had been on phentermine for up to 21 years demonstrated any addictive behavior as assessed by questionnaire and physical examination. Prior studies in the literature in monkeys did not demonstrate significant addictive potential. However, phentermine has a reputation as a “street drug” and is sold in Europe for high prices. Since the combination of phentermine and topiramate has just been approved for long term use in the US, government sponsored, well controlled research into the long term use of generic phentermine is needed. There is no possibility that any private company will do long term research on this generic drug. Should the fears regarding phentermine be shown to be groundless, the positions of governments to ban phentermine should be reconsidered.

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Abstract

Objective:

 

To investigate if phentermine treatment induces phentermine abuse, psychological dependence (addiction) or phentermine drug craving in overweight, obese and weight loss maintenance patients. To investigate whether amphetamine-like withdrawal occurs after abrupt cessation of long-term phentermine treatment.

Design:

 

Clinical intervention trial with interruption of phentermine treatment in long-term patients.

Subjects:

 

269 obese, overweight or formerly obese subjects (age: 20–88 years, BMI: 21–74 kgm−2) treated with phentermine long-term (LTP, N=117), 1.1–21.1 years, or short-term (ATP, N=152), 4–22 days, with phentermine doses of 18.75–112.5 (LTP) and 15–93.75 (ATP) mg per day.

Measurements:

 

Module K of the Mini International Neuropsychiatric Interview modified for phentermine (MINI-SUD), Severity of Dependence Scale (SDS), 45-item Cocaine Craving Questionnaire-NOW (CCQ-NOW) modified for phentermine (PCQ-NOW), and Amphetamine Withdrawal Questionnaire (AWQ) modified for phentermine (PWQ).

Results:

 

MINI-SUD interviews were negative for phentermine abuse or psychological dependence in all LTP patients. SDS examination scores were low for all LTP and ATP patients, indicating they were not psychologically dependent upon phentermine. PCQ-NOW scores were low for all LTP and ATP patients, indicating neither short-term nor long-term phentermine treatment had induced phentermine craving. Other than an increase in hunger or eating, amphetamine-like withdrawal symptoms did not occur upon abrupt phentermine cessation as measured by sequential PWQ scores.

Conclusions:

 

Phentermine abuse or psychological dependence (addiction) does not occur in patients treated with phentermine for obesity. Phentermine treatment does not induce phentermine drug craving, a hallmark sign of addiction. Amphetamine-like withdrawal does not occur upon abrupt treatment cessation even at doses much higher than commonly recommended and after treatment durations of up to 21 years.

Keywords:

phentermine; weight loss; addiction; abuse; dependence; withdrawal

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