Phentermine, an amphetamine congener, is the most widely used anti-obesity drug in the U.S. Although phentermine is the agent-of-choice among physicians specializing in obesity treatment, the use of this drug for obesity treatment by other physicians has long been curtailed because misapprehensions regarding phentermine safety. Concerns of phentermine-induced adverse cardiovascular reactions and of phentermine-induced addiction are two fears that have had a profound negative impact on phentermine prescribing. Although warnings of high incidence rates of adverse cardiovascular and psychiatric effects are included in FDA labeling and are often repeated in published reviews, the few clinical reports in the peer-reviewed medical literature of such adverse effects are anecdotal. Fear of phentermine adverse effects does not inhibit the use of phentermine by obesity treatment specialists. A 2008 survey of prescribing practices found that 98% of bariatric medicine specialists used pharmacotherapy in treating obesity and that 97% of those prescribed phentermine as their first choice. Show
The fear that phentermine has addiction potential appears to be a factor influencing curtailment of use. At the time that phentermine was approved in 1959 the expectations were that it would prove to be addicting, although perhaps less so than amphetamine. These expectations were based on the chemical structural similarities between phentermine and amphetamine and on evidence in rats that phentermine stimulated spontaneous activity. No evidence suggesting the drug had human addiction potential appeared in clinical trials conducted prior to approval. After 52 years of use there is no evidence in the peer-reviewed medical literature to support the hypothesis that phentermine has significant human addiction potential. Research in addiction medicine has undergone significant development in the last 50 years. Concepts of addiction have shifted from an early focus on tolerance and withdrawal to a current emphasis on the psychological components of dependence. Drug addiction has been redefined as drug dependence and standardized diagnostic criteria have been adopted for drug abuse, dependence and withdrawal. Psychometric testing methods have been developed, validated, and applied clinically for measurements of dependence, drug craving, and withdrawal for a wide variety of substances of abuse including cocaine, heroin, and amphetamine. Until recently, none of these addiction medicine metrics had been used to study the addiction potential of phentermine. Presumably, since phentermine is an amphetamine congener, any clinical characteristics of dependence or withdrawal should mimic those of amphetamine dependence or withdrawal. One recent retrospective study investigated symptoms occurring when patients treated with long-term phentermine in a weight management program abruptly ceased taking phentermine. The study found that patients on long-term phentermine who ceased phentermine abruptly by their choice did not have an amphetamine-like withdrawal symptom complex. Significantly there was no evidence of phentermine cravings. Further investigation is warranted. The addiction potential of a drug may be investigated by measuring the drug's propensity to induce dependence, to induce cravings for the drug, and for cessation of the drug to induce characteristic withdrawal symptoms. In the case of amphetamine withdrawal symptoms appear very quickly reaching a maximum at 48 hours after drug cessation. In this prospective study the addiction potential of phentermine will be assessed with validated psychometric scales to examine patients who have taken phentermine long-term for two years or more. Patients who have taken phentermine for 7 to 14 days will also be assessed. Participating patients who have taken phentermine long-term in this study will be asked to interrupt phentermine therapy for 48 hours to participate in the study. Scale examinations will be conducted at 24 and at 48 hours after drug cessation. Hypotheses
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. 2019 Apr;27(4):591-602. doi: 10.1002/oby.22430. Heidi Fischer 3 , Jamy Ard 1 , Lee Barton 3 , Daniel H Bessesen 4 , Matthew F Daley 5 , Jay Desai 6 , Stephanie L Fitzpatrick 7 , Michael Horberg 8 , Corinna Koebnick 3 , Caryn Oshiro 9 , Ayae Yamamoto 3 , Deborah R Young 3 , David E Arterburn 10 Affiliations
Safety and Effectiveness of Longer-Term Phentermine Use: Clinical Outcomes from an Electronic Health Record CohortKristina H Lewis et al. Obesity (Silver Spring). 2019 Apr. AbstractObjective: The aim of this work was to study weight loss and risk of cardiovascular disease (CVD) or death associated with longer-term phentermine use. Methods: Using electronic health record data, 13,972 adults were identified with a first phentermine fill in 2010 to 2015, creating exposure categories according to a patient's duration of use (referent: ≤ 3 months). Multivariable linear models were used to compare percent weight loss across categories at 6, 12, and 24 months, and Cox proportional hazards models were used to compare risk of composite CVD or death, up to 3 years after starting phentermine. Results: The cohort was 84% female and 45% white, with a mean (SD) baseline age 43.5 (10.7) years and BMI of 37.8 (7.2) kg/m2 . In multivariable models, longer-term users of phentermine experienced more weight loss; patients using continuously for > 12 months lost 7.4% more than the referent group at 24 months (P < 0.001). The composite CVD or death outcome was rare (0.3%, 41 events), with no significant difference in hazard ratios between groups. Conclusions: Greater weight loss without increased risk of incident CVD or death was observed in patients using phentermine monotherapy for longer than 3 months. Despite the limitations of the observational design, this study supports the effectiveness and safety of longer-term phentermine use for low-risk individuals. © 2019 The Obesity Society. Comment in
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Can phentermine cause permanent damage?Phentermine may increase your thyroid activity. This may raise your thyroid levels even further. For people with glaucoma: This drug may increase your eye pressure even more. This may cause permanent damage to your vision.
How long can you safely stay on phentermine?Phentermine should only be used for short-term use (less than 12 weeks at a time) to help with weight loss.
Can you be on phentermine longThe authors concluded that phentermine is safe and effective for longer-term use—that is, >3 months—for weight loss in low-risk individuals.
What are the dangers of phentermine?This medicine may cause some people to become dizzy, lightheaded, or less alert than they are normally. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or not alert. This medicine may affect blood sugar levels.
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