Phentermine hydrochloride affects the cardiovascular system in much the same way that fear, excitement and anger do. Essentially an amphetamine, phentermine stimulates the part of the central nervous system that regulates the heart and blood pressure. Physicians prescribe phentermine hydrochloride as part of a weight-loss program because of its ability to increase metabolism and suppress the appetite. The cardiovascular effects of phentermine can cause serious heart problems.
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Phentermine causes the blood vessels of the body to tighten and narrow. Called vasoconstriction, this process increases systemic blood pressure. Blood pressure is made up of a systolic blood pressure--the top and higher number--in a reading that reflects the pressure in the body when the heart beats. The bottom number, called the diastolic pressure, reflects the pressure when the heart is resting between beats. The National Institutes of Health reports phentermine increases systolic and diastolic blood pressure. The higher pressure affects how well the heart can fill with blood during its resting phase. Less blood filling the heart chambers means less blood available to be pumped out to the body. Tight and narrow blood vessels and the consequential high blood pressure force the heart to work harder to pump blood to the body. The lungs are affected by high blood pressure, and a condition called pulmonary hypertension occurs. Patients develop cough, shortness of breath and chest pain. If not corrected, pulmonary hypertension can lead to heart failure.
Irregular Heart Rhythms
Irregular heart rhythms called arrhythmias decrease the effectiveness of the pumping heart. The stimulation effects of phentermine make the cells in the heart more susceptible to electrical impulses. This is referred to as increased excitability, in which the heart begins to have extra heartbeats. You may sense these extra heartbeats or palpitations. Billie Ann Wilson, Ph.D., Margaret Shannon, Ph.D., and Kelly Shields, Pharm.D., authors of “Pearson Nurse’s Drug Guide 2010,” report a common heart problem caused by phentermine is tachycardia. Characterized by a heart rate greater than 100 beats per minute, tachycardia can make you feel short of breath, dizzy and faint. Prolonged tachycardia lowers blood pressure. It can lead to cardiovascular collapse if not corrected.
High blood pressure and vasoconstriction, also known as narrowing of blood vessels, make conditions right for a heart attack. If you have a history of coronary heart disease, you have an increased risk of a heart attack. If taking phentermine, immediately report chest pain, shortness of breath or dizziness to a doctor.
Congestive Heart Failure
A failing heart can occur at any time during use because your underlying health status determines how well the heart can tolerate the effects of phentermine. High blood pressure, vasoconstriction and arrhythmias damage the heart. Report fluid retention, chest pain and shortness of breath to a doctor.
- National Institute of Health Daily Med Sheet: Phentermine Hydrochloride
- “Pearson Nurse’s Drug Guide 2010”; Wilson, B. A., Shannon, T. M., & Shields, K. M.; 2010