Phentermine and Your Heart

Phentermine is the most commonly-prescribed weight loss pill in the United States ( 1 ). While most patients report only minor phentermine side effects, some people experience serious, potentially life-threatening reactions to the medication – including phentermine heart problems.

Can Phentermine Cause Heart Problems?

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.

Thankfully, 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.

Recent evidence indicates that phentermine may also increase patients’ risk of coronary vasospasm.

For this reason, phentermine is only available under a doctor’s prescription & supervision, and each patient must be evaluated individually before receiving a script for this medication.

Serious Phentermine Heart Problems

Valvular heart disease and primary pulmonary hypertension are two serious, heart-related side effects of phentermine. These complications were first identified in patients who took phentermine plus fenfluramine.

Fen-Phen (or Phen-Fen) was an off-label combination of these two medications that grew popular in the late 80s and early 90s and gained renown for its ability to help patients shed weight quickly and easily.

However, fenfluramine (and its more potent cousin: dexfenfluramine) was withdrawn from the market in 1997 after a prominent Mayo Clinic study linked use of Phen-Fen to an increased risk of pulmonary hypertension and heart valve disease ( 2 ).

While phentermine alone was never implicated in these reports, causative involvement cannot be ruled out. As a result, these potentially-fatal conditions are still listed as side effects of any medication containing phentermine.

Phentermine Heart Valve Problems

The serendipitous discovery of a connection between Phen-Fen use and serious heart valve problems arose from informal communications between doctors at the Mayo Clinic and around the country in the mid-1990s.

The physicians noticed that 24 different female patients treated with Phen-Fen had developed leaky, misshapen, and discolored valves after using the two weight-loss medications for about one year.

This was problematic because 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. In patients who required surgical intervention, surgeons noted heart valves had an atypical “glistening white appearance” ( 2 , 3 ).

Among the 113 Phen-Fen heart valve cases reported to the FDA in 1997, none of the affected patients took phentermine alone. This makes sense, given that the damage was eventually linked with activity of the 5-HT2b receptor on heart valves. Phentermine alone is not drawn to this receptor.

Notably, 16% of the affected patients had taken fenfluramine or dexfenfluramine alone, without phentermine ( 4 ). As a result, fenfluramine and dexfenfluramine were withdrawn from the market, but phentermine remained available for pharmaceutical weight loss.

Below is the official warning about phentermine and heart valve problems as written on the Adipex-P drug label ( 5 ):

“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.”

Phentermine and Pulmonary Hypertension

Eight of the twenty-four women in the initial Mayo Clinic report also presented with primary pulmonary hypertension (PPH) after taking Phen-Fen ( 2 ).

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: the vessel that carries blood from the heart to the lungs. It can be fatal if left untreated ( 6 ).

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 ( 5 ):

“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.”

Phentermine and Coronary Vasospasm

Although not listed on the medication’s official label, a 2019 case report from the Mayo Clinic suggests a potential link between phentermine use and increased risk of coronary vasospasm, especially in patients with a history of nicotine use or arthrosclerosis ( 9 , 10 ).

Coronary vasospasm is the sudden narrowing of the blood vessels in the heart. It causes extreme chest pain that can feel like a heart attack and may lead to further complications if left untreated (including heart attack).

Vasospasm is already a documented as potential reaction to other legal and illegal stimulant drugs – including amphetamines, which are chemically-similar to phentermine ( 11 ). So, speak with your doctor about this possible risk before starting phentermine.

Other Effects of Phentermine on the Heart

Serious phentermine heart problems are always possible, and very serious, but not as common as other phentermine effects on the heart, such as racing pulse, increased blood pressure, and irregular heartbeat.

In fact, almost 1 in 4 phentermine users reported some type of heart or blood pressure problem while taking this medication ( 12 ).

Phentermine and Heart Rate

Increased blood pressure and tachycardia (fast heart rate) are listed side effects of phentermine ( 5 ).

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 ( 13 ).

However, stimulant medications like phentermine can raise heart rate and blood pressure well above normal ranges. The pills’ effect on the heart are part of the reason that phentermine is not suitable for patients with 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 ( 14 ).

Therefore, it is critical that the prescribing physician monitor heart rate and blood pressure throughout treatment. For some patients, it may also be beneficial to monitor heart rate and blood pressure at home between appointments.

Phentermine and Heart Palpitations

Heart palpitations are another potential side effect of phentermine weight loss pills ( 5 ). A heart palpitation is when it feels 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 cause it to beat slightly outside of its normal rhythm. However, these palpitations may also 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.

Signs of Phentermine Heart Problems

These symptoms can indicate a serious phentermine side effect. Seek professional medical attention immediately if you notice these or any other unusual reactions while taking phentermine.

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