Long-term Effects of Phentermine on Metabolism (updated)

June 16, 2022 |

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Phentermine does not affect metabolism directly. Thus, it does not have any long-term effect on it. But it may leave some impact on your other body systems.

Who does not want to retain the weight loss progress they achieved with their diet pill? And it is only possible if the treatment they are taking leaves a lifelong or at least a long-term impact on their metabolism.

But unfortunately, phentermine promotes weight loss by stimulating your sympathetic nervous system, which at most can suppress appetite and give you an energy boost.

From this article, you will learn if and how phentermine affects your metabolism, its long-term side effects, and what are the better metabolism-boosting alternatives out there.

So, keep reading to find out all the details.

How does phentermine affect metabolism?

Phentermine formula

I hate to break it to you, but according to some high authority sources, it has been confirmed that phentermine does not directly affect your metabolism.

However, there are ways in which it may influence your metabolic rate indirectly. Here’s how it works;

Phentermine is a sympathomimetic amine, and it basically improves weight loss by messing with your neurotransmitters to suppress appetite and boost energy.

The effect of phentermine on your energy levels and neurotransmitters like leptin may help increase your metabolism.

Let me elaborate on these two aspects of phentermine.

Recent research has found that your lean muscle mass percentage determines your metabolic rate.

And interestingly, 20% of your total daily energy expenditure is contributed by lean muscle tissue compared to only 5% by fat tissue (these percentages are standardized for individuals with about 20% body fat).

Phentermine causes an increase in your energy levels which may not only motivate you to hit the gym but also allows you to do some extra reps there.

By aiding your workout routine with its energy-boosting effect, phentermine is helping you lose the excess fat and build lean muscle.

And since lean muscle tissue is more metabolically active than fat tissue, this may increase your metabolism rate and allow you to burn more calories in a resting state.

According to phenterminedoctors.com, phentermine is theorized to increase the leptin levels in the brain, which signals satiety.

Leptin is an adipocyte-derived hormone, and it acts on the neurons and certain areas of the brain to signal different mechanisms in the body that help keep obesity in check.

In addition to its benefit in regulating your eating behavior, a 2015 study on Turkish participants receiving leptin therapy reported that leptin prevents the reduction in metabolic rate in the subjects. Which is one of the many ways in which it contributes to decreasing your body weight, body mass index (BMI), and fat mass.

What are the long-term effects of using phentermine?

As I have explained above, phentermine is not primarily designed to target and boost your metabolism. Thus, it may show long-term effects on only the organs and organ systems that it primarily affects.

You now know that phentermine messes with your sympathetic nervous system and your brain’s neurotransmitters.

So, you may expect it to leave a long-term influence on your mental state, cardiovascular state, vision, etc.

Let us get into the details of these effects.

1. Psychological side effects

Phentermine stimulates the central nervous system, so it may be expected to trigger anxiety, depression, or psychosis in the users.

However, these effects start to disappear for most people after discontinuing the prescription.

But there are also reports that phentermine uncovered some underlying affective illness in certain people from which they had to suffer for many more years to come.

A 2011 article compiled 4 case reports that documented psychological side effects caused due to phentermine, and out of these, two case reports suggest long-term psychological side effects.

In one of these case reports, a 30-year-old woman who was never pre-diagnosed with any psychotic illness but had a family history of affective disorders started taking phentermine. She began to develop paranoid delusions within one week of starting treatment.

And since she continued taking the prescription, her condition worsened, and after 12 months, her family could discern a link between her diet pills and her worsening psychological condition.

She discontinued the prescription soon after and started to receive antipsychotic treatment, which made her better.

But, over the following five years, she was reported to receive treatment for her psychosis, which suggests that phentermine might have uncovered schizophrenia-like illness in her.

In another case report, a 52-year-old man with no history of affective illness started to self-medicate himself with phentermine.

He reported having developed auditory hallucinations and delusions within two weeks of its use.

Although his symptoms resolved after discontinuing phentermine, he continued to report depressive symptoms four years later.

2. Primary Pulmonary Hypertension (PPH)

Phentermine initiates a fight and flight response in your body which may influence your blood vessels.

It may constrict your blood vessels and increase your blood pressure.

Phentermine administration, either alone or in combination with other drugs, has been associated with the development of a rare and fatal lung disease known as Primary Pulmonary Hypertension.

Primary Pulmonary Hypertension refers to a condition in which the blood pressure in the lung increases due to the narrowing down of the blood vessels in the lung.

It may also lead to heart failure if not timely treated.

Most patients developing this condition are young women. And it is advised that you immediately report to the doctor if you start observing a decrease in your exercise tolerance due to your phentermine treatment.

The initial symptom of this disease could be shortness of breath, chest pain, loss of consciousness, or accumulation of fluid in the lower legs. Other symptoms may include fatigue, dry cough, dizziness, bluish lips and skin, racing pulse, or irregular heartbeat.

There are multiple case reports in which patients developed Primary Pulmonary Hypertension (PPH) after getting phentermine-fenfluramine combination therapy.

One case report also serves as evidence that phentermine monotherapy may also lead to the development of this disease in the user.

In a 1997 case report, an apparently healthy 29-year-old woman with no family history of pulmonary hypertension started observing her phen-fen combination treatment.

Soon after, she reported symptoms like shortness of breath and increased heart rate after moderate exercise.

She discontinued this treatment after 23 days and observed recovery in her symptoms.

But after five months, she started getting the same symptoms and ultimately died due to cardiac arrest.

This is one of the many scientific evidence suggesting that pulmonary hypertension may occur as a long-term side effect of phentermine combination treatment.

In addition to this, a 2010 case report is the first and only evidence for phentermine-induced pulmonary hypertension.

According to it, a 29-year-old woman was admitted to the hospital due to shortness of breath. She was later diagnosed with Pulmonary Hypertension.

Although she recovered with treatment, it was later confirmed that she had undergone phentermine monotherapy three months ago for five weeks.

3. Valvular heart disease

A constant fight and flight mode induced in the body by phentermine may strain your heart because it is continuously beating faster.

Thus, it may lead to heart-related side effects.

There is significant evidence suggesting that taking phentermine alone or as a combination therapy with other drugs may cause defects in any of the four heart valves, a condition termed valvular heart disease.

Cardiac valvular disease may affect either one or multiple heart valves simultaneously. The most affected heart valves are the mitral, aortic, and tricuspid valves.

If you develop this condition, you may encounter shortness of breath, chest pain, fatigue, dizziness, irregular heartbeat, or fever.

According to CDC, there are multiple case reports in which patients had developed a valvular disease after being treated with different phentermine combination therapies.

It could be a combination of phentermine with fenfluramine and dexfenfluramine. It mentions 89 case reports in which patients developed the valvular disease after taking a combination of fenfluramine and phentermine.

There are 6 case reports that document patients developing this disease after using a combination of phentermine, fenfluramine, and dexfenfluramine.

According to the documented case reports, mostly women aged 22 to 68 with a median age of 44 years had developed phentermine-associated valvular heart disease.

It mainly affected the left side of the heart, involved multiple valves, and was of rapid onset.

Moreover, the duration of therapy for these patients varied between 1 to 39 months and was 9 months in most cases.

In all these case reports, fenfluramine and dexfenfluramine were found to have a more significant role in causing valvular diseases.

Thus, FDA called for their voluntary withdrawal from the market. But this does not rule out the possibility that phentermine might also contribute to this disease in the case reports.

Moreover, this 2006 case report is evidence of heart valve disease caused by phentermine monotherapy. In this case, a 28-year-old woman taking phentermine for the past eight months was diagnosed with an aortic heart valve rupture.

But scientists could not chalk out any conclusive and definitive link between the treatment and the disease because she was also suffering from co-morbidities.

4. Damage vision

Phentermine is sending your body into an alert phase, and this means that you need to keep your eyes open, which equates to pupil dilation.

This means that phentermine is affecting your eyes as well. Thus, it is not recommended for patients diagnosed with glaucoma because it increases the pressure on the eyes.

Blurred vision is also one of the commonly reported side effects of phentermine. But cases of permanent damage to the eyesight caused due to phentermine combination therapy have also been reported in otherwise healthy individuals.

According to a 2015 case report, a 39-year-old-women was taken to the hospital because she complained of vision loss and pain in both eyes one week after administering a treatment with Qsymia. (Qsymia is a combination of phentermine and topiramate extended-release tablets.)

The woman was reported to have been diagnosed with acute bilateral angle-closure that could have ended up causing blindness in case her treatment was delayed.

This shows that phentermine combination therapies may cause life-threatening adverse effects that may last long.

PhenQ – The Safer Phentermine

Since phentermine has multiple long-term side effects, it is better to opt for an all-natural weight loss supplement that has minimal and self-limiting side effects.

PhenQ is one such over-the-counter diet pill that works in five ways to help you lose weight. It suppresses appetite, initiates fat burning, prevents fat formation, boosts energy, and improves mood.

It also has thermogenic boosters like capsimax powder and caffeine, which may speed up your metabolism.

There are over 190,000 reviews that vouch for PhenQ. And it does not pose a risk of life-threatening and long-term side effects like phentermine.

The most complaints you might get are a mild headache, mild jitters, and mild gastrointestinal symptoms like constipation, nausea, or diarrhea. These, too, are very rarely reported.


All in all, phentermine does not affect metabolism directly. But one thing is for sure; it won’t slow down your metabolism.

Nonetheless, it may leave a long-term effect on your other organs and organ systems.

The long-term effects of phentermine could be on your central nervous system, cardiovascular system, or vision.

However, if you want something to increase your metabolism rate, then PhenQ would make a better option. The reason is that PhenQ has thermogenic properties that may speed up your metabolism.

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