Phentermine is a prescription diet pill that's used for weight loss, and is mainly used as an appetite suppressant. Since receiving FDA approval in 1959, Phentermine has been used worldwide as a prescription diet pill to help people lose weight.
Various studies have been done on Phentermine to study its effectiveness for weight loss, and to determine possible side effects of using Phentermine. In this article, we highlight several Phentermine studies done in the past that evaluate the effectiveness of the Phentermine prescription diet pill.
Phentermine Study I (Phen Fen vs. Phen Flu)
Study origin: Department of Medicine and Nutritional Sciences, University of Wisconsin, Madison, WI, USA.
Title: Comparison of combinations of drugs for treatment of obesity: body weight and echocardiographic status (International Journal of Obesity advance online publication, 5 December 2006;)
Phentermine Background: Obesity treatment with single drugs produces weight losses of about 8-10% of initial body weight. Few studies of combinations of drugs for treating obesity have been published. The combination of phentermine, an adrenergic agent, and fenfluramine, a serotonergic agent, (phen-fen) produced weight losses of about 15% of initial body weight. Fenfluramine is no longer available because it was associated with cardiac valve lesions. Phentermine-fluoxetine (phen-flu) has been proposed as an alternative for phen-fen.
Objective: To compare the efficacy of treatment and prevalence of cardiac valve abnormalities on phen-flu vs phen-fen.
Design: Retrospective chart review of all patients treated for at least 3 months with phen-flu (N=97) to a random sample of patients treated with phen-fen (N=98) in the Clinical Nutrition Clinic at the University of Wisconsin. Comparison of echocardiograms in all patients treated solely with phen-flu (N=21) to a random sample of patients treated with phen-fen (N=47), and to a group of subjects never treated with obesity drugs (N=26).
Results: With last observation carried forward analysis (LOCF), at 6 months of treatment the phen-fen patients lost 12.6+/-0.6% of baseline weight and phen-flu patients lost 9.0+/-0.6% (P<0.001). With completers analysis, there were no significant differences in weight loss as a percent of baseline weight at 6 months (14.4+/-0.6 vs 13.3+/-0.9%). LOCF decreases in body mass index (BMI) at 6 months were -5.3 and -3.6 kg/m(2) for phen-fen and phen-flu, respectively (P<0.001), and 6.2+/-0.3 vs 5.4+/-0.4 kg/m(2), respectively, for the completers analysis (P - NS).
Dropout rate at 6 months was higher in phen-flu subjects (44 vs 28%). In subjects without atherosclerosis of valves (presumably pre-existing), cardiac valve lesions occurred in eight of 38 phen-fen subjects and in none of 15 phen-flu subjects or 25 control subjects who had not been treated with drugs.
Conclusions: The combination of phentermine and fluoxetine was not as effective as phen-fen, but was not associated with cardiac valve lesions. Longer term, larger scale studies of phen-flu are warranted.
Phentermine Study II (Phentermine 37.5)
Study Origin: Department of Family Medicine, Yonsei University College of Medicine, 134 Shinchon-dong, Seodaemun-gu, Seoul 120-752, Korea.
Title: Effects on weight reduction and safety of short-term phentermine administration in Korean obese people.
Researchers: Kim KK, Cho HJ, Kang HC, Youn BB, Lee KR.
Objective: Phentermine, an appetite suppressant, has been widely applied in Korea since 2004. However, there have been relatively few reports about the efficacy and the safety of phentermine in Korea. The aim of this study is to verify the effect of phentermine on weight reduction and the safety in Korean patients.
Design: This randomized, double-blind, placebo- controlled study had been performed between February and July, 2005, in Seoul on 68 relatively healthy obese adults whose body mass index was 25 kg/m2 or greater. They received phentermine-HCl 37.5 mg or placebo once daily with behavioral therapy for obesity.
Results: The primary endpoints were the changes of body weight and waist circumference from the baseline in the intention-to-treat population. Mean decrease of both body weight and waist circumference in phentermine-treated subjects were significantly greater than that of placebo group (weight: -6.7 +/- 2.5 kg, p < 0.001; waist circumference: -6.2 +/- 3.5 cm, p < 0.001). Significant number of subjects in phentermine group accomplished weight reduction of 5% or greater from the baseline and 10% or more (p < 0.001).
There were no significant differences in systolic and diastolic blood pressure between the groups (p = 0.122 for systolic BP; p = 0.219 for diastolic BP). Dry mouth and insomnia were the only statistically significant adverse events that occurred more frequently in phentermine group. Most side effects of phentermine were mild to moderate in intensity.
Conclusion: Short-term phentermine administration induced significant weight reduction and reduction of waist circumference without clinically problematic adverse events on relatively healthy Korean obese people.
Phentermine Study III (Phen-Fen)
Study Origin: Department of Psychiatry, University of Pennsylvania School of Medicine, Philadelphia, 19104, USA.
Title: The fen-phen finale: a study of weight loss and valvular heart disease.
Researchers: Wadden TA, Berkowitz RI, Silvestry F, Vogt RA, St John Sutton MG, Stunkard AJ, Foster GD, Aber JL.
Objective: To assess weight loss, as well as the prevalence of valvular heart disease, in 21 obese women who completed 2 years of treatment by fenfluramine and phentermine (fen-phen) in June 1997.
Design: Patients were 21 of 22 women who had completed a 1-year, open-label trial of fen-phen combined with lifestyle modification. This study describes the results of a second year of treatment. The presence of valvular heart disease, defined as aortic regurgitation of mild or greater severity and/or mitral regurgitation of moderate or greater severity, was assessed using two-dimensional, color Doppler and pulsed- and continuous-wave Doppler examinations.
Results: At 2 years, the 21 patients had a mean reduction in initial weight of 13.9 + 10.0%, which was significantly (p<0.001) smaller than their 1-year loss of 17.1 +/- 8.7%. Nine of 21 patients reported that they took fen-phen irregularly during the last 4 months of the study because of fears of developing health complications. These nine patients had a 2-year weight loss of 8.7 +/- 7.5%, compared with a significantly (p<0.04) larger loss of 17.6 +/- 10.5% for participants who reported taking medication regularly. Six of 20 (30%) patients met criteria for valvular heart disease. None of the six had signs or symptoms of this condition.
Discussion: Fenfluramine was withdrawn from the market on September 15, 1997 because of concerns that it was associated with valvular heart disease. The present findings are discussed in terms of the potentially favorable long-term benefits of combining lifestyle modification with weight loss medications that are both safe and effective.