Phentermine is the most commonly-prescribed weight loss pill in the United States . Most patients successfully undergo treatment and report only minor phentermine side effects, but some people experience very serious, potentially life-threatening reactions to the medication. For this reason, a doctor must thoroughly evaluate current health status and the utility of pharmacotherapy in each patient's specific case before prescribing phentermine. This mandatory process is in-place to ensure that the expected reward outweighs any potential risk of phentermine heart problems or other serious complications.
Yes, phentermine can cause heart problems.Two listed side effects of this medication are valvular heart disease and primary pulmonary hypertension: both critical cardiopulmonary problems. However, these serious side effects are rare in patients taking phentermine alone. The medication more frequently causes other cardiovascular problems, such as increased (or irregular) heart rate or high blood pressure.
Two of the most serious potential side effects of phentermine are cardiac valvular disease and primary pulmonary hypertension. These complications were first identified among patients taking the once-popular combination of phentermine and fenfluramine or dexfenfluramine.
Fen-Phen (or Phen-Fen) was an off-label combination of two weight loss medications: phentermine (“phen”) and fenfluramine (“fen”) that grew popular in the late 80s and early 90s. The duo gained renown for its ability to help patients shed weight quickly and easily.
However, fenfluramine (and its more potent cousin, dexfenfluramine) were withdrawn from the market in 1997 after a prominent Mayo Clinic study linked Phen-Fen use to an increased risk of pulmonary hypertension and heart valve disease .While phentermine alone was never implicated in these reports, causative involvement cannot be ruled-out. As a result, these potentially-fatal side effects are still considered possible adverse side effects of any pill containing phentermine.
Informal communications between doctors at the Mayo Clinic and other practices around the country led to the serendipitous discovery of a connection between Phen-Fen use and serious heart valve problems. Among a group of 24 female patients treated with Phen-Fen for an average of 12 months each, all presented with “unusual valvular morphology and regurgitation” on both sides of the heart. In patients who required surgical intervention, heart valves had a “glistening white appearance” .
In other words, patients presented with leaky, misshapen and discolored valves on both sides of their heart after using Phen-Fen for about one year. When a valve is leaky the heart has to work harder to pump the same amount of blood. Depending on the degree of damage, leaky heart valves may be either repaired or replaced .
This damage was eventually linked with activity of the 5-HT2b receptor on heart valves. Phentermine alone is not drawn to this receptor. More, among the 113 Phen-Fen heart valve cases reported to the FDA in 1997, none of the affected patients took phentermine alone. Notably, 16% of patients had taken fenfluramine or dexfenfluramine alone . As a result, fenfluramine and dexfenfluramine were withdrawn from the market, but phentermine remined available for pharmaceutical weight loss.
Below is the official warning about phentermine and heart valve problems as written on the Adipex-P drug label :
“Serious regurgitant cardiac valvular disease, primarily affecting the mitral, aortic and/or tricuspid valves, has been reported in otherwise healthy persons who had taken a combination of phentermine with fenfluramine or dexfenfluramine for weight loss. The possible role of phentermine in the etiology of these valvulopathies has not been established and their course in individuals after the drugs are stopped is not known. The possibility of an association between valvular heart disease and the use of phentermine alone cannot be ruled out; there have been rare cases of valvular heart disease in patients who reportedly have taken phentermine alone.”
Eight of the 24 women in the initial Mayo Clinic report also presented with primary pulmonary hypertension (PPH) after taking Phen-Fen .
PPH is a rare condition in which the small blood vessels in the lungs narrow and force blood pressure to increase precipitously in the pulmonary artery, which carries blood from the heart to the lungs. It can prove fatal if left untreated . A 2010 article suggested a link between phentermine monotherapy and the development of pulmonary hypertension, but these findings are not universally accepted [7,8].
Below is the warning about primary pulmonary hypertension, as printed on the same Adipex-P drug label :
“Primary Pulmonary Hypertension (PPH) – a rare, frequently fatal disease of the lungs – has been reported to occur in patients receiving a combination of phentermine with fenfluramine or dexfenfluramine. The possibility of an association between PPH and the use of phentermine alone cannot be ruled out; there have been rare cases of PPH in patients who reportedly have taken phentermine alone. The initial symptom of PPH is usually dyspnea. Other initial symptoms may include angina pectoris, syncope or lower extremity edema. Patients should be advised to report immediately any deterioration in exercise tolerance. Treatment should be discontinued in patients who develop new, unexplained symptoms of dyspnea, angina pectoris, syncope or lower extremity edema, and patients should be evaluated for the possible presence of pulmonary hypertension.”
The above side effects are always possible and very serious, but not as common other phentermine effects on the heart such as racing pulse, increased blood pressure and irregular heartbeat. In fact, 23% of recent phentermine users reported having some type of heart or blood pressure problem while undergoing treatment with this medication .
As a central nervous system stimulant, phentermine has the potential to increase heart rate and blood pressure. As such, increased blood pressure and tachycardia (fast heart rate) are listed as potential adverse reactions of this medication . User reports commonly corroborate this link between phentermine and increased heart rate and blood pressure. Understandably, then, phentermine use is contraindicated in the presence of cardiovascular disease or uncontrolled high blood pressure.
Interestingly, some recent research indicates that phentermine does not significantly increase heart rate or blood pressure when taken as prescribed .
Nonetheless, your prescribing physician should closely monitor all vital signs throughout the course of treatment to ensure that you are not experiencing an adverse reaction to phentermine. It may also prove beneficial for you to monitor heart rate and blood pressure at home, between appointments. A normal heart rate is 60-100 beats per minute, while optimal is blood pressure is around 120/80 mm Hg for the average adult . However, these numbers vary slightly between individuals, so it is important to work with your doctor to establish a healthy baseline for you.
Heart palpitations are another potential side effect of phentermine weight loss pills . A heart palpitation is when it feel like your heart is pounding, fluttering or skipping a beat. Phentermine heart palpitations occur because, as a stimulant, this drug makes your heart more sensitive to electrical signals and may cuase it to beat slightly outside of its normal rhythm. Still, phentermine heart palpitations may indicate a more serious problem and can prove dangerous if not corrected .
Call your doctor or seek medical attention right away if you feel like your heart is pounding, fluttering or beating irregularly while taking this medication.
The above reactions can indicate a serious phentermine side effect. Seek professional medical attention immediately if you notice these or any other unusual symptoms while taking phentermine.
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2. Connolly, H. M., Crary, J. L., McGoon, M. D., Hensrud, D. D., Edwards, B. S., Edwards, W. D., & Schraff, H. V. (1997). Valvular Heart Disease Associated with Fenfluramine–Phentermine. New England Journal of Medicine, 337(24), 1772-1776. doi:10.1056/nejm199712113372414
3. American Heart Association. (2016, May 31). Problem: Heart Valve Regurgitation.
4. Centers for Disease Control and Prevention. (1997). Cardiac Valvulopathy Associated With Exposure to Fenfluramine or Dexfenfluramine: US Department of Health and Human Services Interim Public Health Recommendations, November 1997. JAMA: The Journal of the American Medical Association, 278(21), 1729. doi:10.1001/jama.1997.03550210025016
5. U.S. Food and Drug Administration. (2012). Adipex-P (phentermine hydrochloride) capsules label [Brochure].
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10. Hendricks, E. J., Greenway, F. L., Westman, E. C., & Gupta, A. K. (2011). Blood Pressure and Heart Rate Effects, Weight Loss and Maintenance During Long-Term Phentermine Pharmacotherapy for Obesity. Obesity, 19(12), 2351-2360. doi:10.1038/oby.2011.94
11. Cleveland Clinic Heart & Vascular Team. (2018, December 13). True or False? 6 Common Beliefs About Blood Pressure, Heart Rate.
12. Nevins, P. (n.d.). Heart Problems Caused by Phentermine.
13. WebMD. (2019). Phentermine Oral : Uses, Side Effects, Interactions, Pictures, Warnings & Dosing.
14. CardioSmart: American College of Cardiology. (2011, November 21). Phentermine.