Phentermine and High Blood Pressure: Is It Safe?

by Marixie Ann Obsioma, MT, undergrad MD on July 12, 2024
Last updated on July 12, 2024

More and more people worldwide find themselves wrestling with a BMI over 30 kg/m2, plunging into the heavy territory. Such a hefty problem drags along serious health woes, including soaring blood pressure and heart-related hiccups.

Nurse measuring patient blood pressure

The primary and best approach for the management of obesity and related comorbidities is lifestyle modification that includes calorie restriction and increased physical activity.

This approach, however, is of modest efficacy because of poor long-term adherence. Additional interventions were introduced like bariatric surgery and pharmacotherapy.

Losing weight is really good for the heart, but drugs to achieve it might not have the same effect. For millions of overweight or obese people, popping a pill to get healthier quickly might seem appealing. But for some users, these medications can dangerously affect their heartbeat rhythms.

A wide variety of these drugs are available, both OTC and by prescription. One of the most popular brands is Phentermine. While it has been proven to be effective in helping people shed off extra fat, it does come with some side effects, especially when used excessively.
Is high blood pressure one of its downsides? Let’s find out by discussing Phentermine in details.

What is Phentermine?

Phentermine is a sympathomimetic amine drug used for the treatment of weight loss. It is generally prescribed for patients who have a body-mass index of more than 30.

It works by stimulating the secretion of noradrenaline in the CNS. It also curbs appetite by regulating the β-adrenergic receptors (1).

This is a controlled substance, and must only be taken with a prescription for not more than 3 weeks (2).

Phentermine was first approved as a diet pill in 1959. It has been on the market in different forms since then. However, in the late 1990s, the FDA removed a combination diet pill known as fen-phen, which stands for Fenfluramine and Phentermine, because of its damaging effects to heart valves (2).

What are the possible side effects of Phentermine?

The more common side effects of Phentermine include headache, vomiting, dry mouth, diarrhea, constipation, and insomnia. These effects are mild and usually go away within a few days (3). Insomnia can be prevented by taking the drug early in the morning.

When not taken properly and excessively, Phentermine can also cause serious side effects. These symptoms can be life-threatening and may require immediate medical attention:

  • Primary Pulmonary Hypertension (PPH). This type of high blood pressure affects the lung arteries and the right side of your heart. Common complaints include shortness of breath, palpitations, chest pain, cyanosis, dizziness, tiredness, and edema.
  • Valvular Heart Disease. Phentermine can harm your heart valves. They may not close properly and cause leakage. Patients with this condition usually complain of fatigue, weakness, shortness of breath, chest pain, lightheadedness, heart murmur, palpitations, and edema.
  • Hypertension
  • Tremors
  • Restlessness
  • Erectile Dysfunction in Men

Obviously, Phentermine can cause high blood pressure and other heart problems. But how?

How Does Phentermine Cause Heart Problems?

Phentermine causes narrowing and tightening of the blood vessels, which causes an increase in systemic blood pressure (4).

Blood pressure is made up of systolic and diastolic blood pressure. The former reflects the pressure in the body when the heart beats. The latter refers to the pressure when the heart is at rest.

According to the National Institutes of Health, Phentermine can increase both systolic and diastolic blood pressure. This greatly affects how the heart can fill with blood during rest. If there is less blood filling the heart chambers, there will be a decreased blood supply to different body areas (4).

Narrow and tight vessels and high blood pressure make the heart work harder to be able to pump out blood effectively. The lungs are likewise affected, and a condition known as pulmonary hypertension may occur. Patients will soon start to experience coughing, shortness of breath, and chest pain. If not treated immediately, it may cause heart failure (4).

Phentermine may also cause arrhythmias. As a stimulant, Phentermine makes the heart cells more susceptible to electrical impulses. There is increased excitability, hence the heart starts to have extra beats. Patients may sense these as palpitations.

One study also reported a case of supraventricular tachycardia, a heart rate of more than 100 beats per minute, in a healthy patient taking Phentermine (5). If left untreated, tachycardia can lower blood pressure, which will eventually lead to cardiovascular collapse if not treated.
An increased heart rate weakens your heart muscles and may cause congestive heart failure. A very fast heart rate can also cause your BP to drop low, causing blackouts (6).

A failing heart may occur at any time. Your underlying health status will determine how well your heart can tolerate the effects of Phentermine. High blood pressure, arrhythmias, and vasoconstriction can damage the heart. And if you have a history of coronary heart disease, you are also prone to heart attack.

Weigh the Risks and Benefits

Patients who are either overweight or obese are at risk for serious health problems like diabetes, heart diseases, and stroke. On top of all that, extra weight, as mentioned earlier, makes your heart work harder.

You have to know if you are at risk. Do you have a history of hypertension and heart diseases? How bad is it?

Taking Phentermine and other weight-loss medications can cause similar heart conditions. That’s because they often contain stimulants, which make patients more alert and less interested in food. While speeding up metabolism, these drugs may likewise increase your heart rate. In patients susceptible to arrhythmia, these drugs may act as triggers.

Still, weight-loss drugs may be appropriate for some patients. One study found that obese people who are having a hard time saying no to food cues found great help with weight-loss medications (7).

If you need to be on Phentermine treatment but is worried about increasing your blood pressure, you can take some natural preventive measures to lessen your risk.

Natural Ways to Lower Blood Pressure

There are several things that you can do to help lower your blood pressure naturally, even without drugs. Listed below are 5 of the most important tips:

1. Exercise Regularly

Exercise is among the best things one can do to lower blood pressure.

Regular exercise can help make your heart stronger and more efficient at pumping blood.

Based on studies, exercises like walking and running can help decrease BP and improve your overall health (8, 9).

Exercise for at least half an hour daily to help lower your blood pressure.

2. Take Less Sodium

Processed foods are everywhere and they contain high amounts of sodium.

Though genetic differences may still play a role, most studies would associate high salt intake with high blood pressure and heart problems such as stroke (10, 11).

It’s worth cutting back your sodium intake. Switch to fresh produce and season using herbs and spices instead of salt.

3. Eat Potassium-Rich Foods

Potassium can decrease sodium and ease pressure on your blood vessels (12).

One must focus on eating fresh, whole foods like leafy greens, potatoes, tomatoes, bananas, oranges, melons, avocados, apricots, yogurt, milk, salmon, tuna, nuts, and beans.

4. Avoid Caffeine

Caffeine can cause a spike in your blood pressure. Though it does not cause a lasting increase for some people, cutting back on coffee and tea can be helpful if you are on Phentermine treatment.

5. Limit Alcohol

Alcohol can increase blood pressure. One study revealed that 16% of high BP cases worldwide are linked to alcohol use (13).

It is best not to exceed one drink for women and two for men.

The Bottom Line

Before resorting to Phentermine use and the possible risks involved, consider safer options like the tips mentioned above. If you still choose to lose weight through medication, be sure to take it religiously as prescribed and work closely with a medical professional. Be sure to safeguard your heart health while embarking on your weight-loss journey.


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