Phentermine And High Blood Pressure: Is It Safe?

by Dr. Ahmed Zayed
Published on June 12, 2024
blood pressure test

Just got started with Phentermine, or maybe it’s already part of your routine? Bet you’re wondering how it’ll affect your well-being. You know, like tons of meds out there, phentermine might stir up some side effects or clash with other stuff you’re on. It’s totally normal to ponder its safety, particularly if battling high blood pressure is on your to-do health list.

Throughout this post, we’re going to focus on phentermine and discuss whether you can take it if you have high blood pressure or not. Scroll down to learn more.

How does phentermine work?

Phentermine is one of the most frequently prescribed drugs for weight loss. Yes, the drug is available with a doctor’s prescription only due to its strength. This is not a dietary supplement or some other weight loss product you can buy in drugstore or order online. Phentermine is a generic form of drugs that are sold under brand names such as Adipex-P and Suprenza (1).

This is a psychostimulant medication that belongs to drugs called substituted amphetamine which is a chemical class of medications similar to amphetamine. Phentermine was specifically formulated to suppress appetite in order to reduce calorie intake and help kick-start weight loss in persons whose BMI is 30 (or 27 in the presence of cardiovascular risk factors and other problems associated with obesity).

Phentermine is used as an adjunct to doctor-approved exercise, calorie restriction, and lifestyle changes to help men and women lose weight (2). As a short-term solution (up to 12 weeks or three months), phentermine works when you make an effort. It’s a huge mistake to take the pill hoping it would magically work without exercising or making any changes in your diet.

The drug works by stimulating your brain to decrease appetite, but also it helps burn calories faster. Phentermine stimulates the release of certain neurotransmitters such as dopamine, epinephrine (adrenalin), and norepinephrine (noradrenaline) to boost energy levels, increase alertness, and minimize cravings. It’s a well-known fact that cravings (usually for unhealthy food) are one of the biggest enemies for successful weight loss and effective weight management. This way, phentermine allows users to slim down and maintain their results.

Approved since 1959, phentermine is thanks to its efficacy and reasonable price one of the drugs with the oldest seal of approval from FDA (3). Not only it promotes weight loss on its own, but the drug also works well in combination with other medications such as topiramate (4, 5).

High blood pressure causes and risk factors

Hypertension or high blood pressure occurs when the force of blood pushing against blood vessel walls is higher than normal (6). Millions of people have hypertension. More precisely, an estimated 103 million US adults have high blood pressure, according to the American Heart Association, which is nearly half of all adults in the country. The death rate caused by hypertension increased by 11% in a period between 2005 and 2015. On a global level, about a third of the adult population worldwide has high blood pressure, and with the aging population alongside increased life expectancy those numbers are bound to rise (7).

Most people with hypertension don’t have any symptoms which only depicts the severity of this problem. However, in some cases, a person can have a headache, nosebleeds, shortness of breath, but none of them are specific symptoms that affect everyone with high blood pressure. It’s highly important to monitor your blood pressure regularly in order to manage it effectively.

As far as the causes of hypertension are concerned, it’s important to differentiate between primary and secondary high blood pressure. Primary hypertension does not have a specific cause, and it tends to develop over many years. On the flip side, secondary hypertension involves some underlying cause such as obstructive sleep apnea, adrenal gland tumors, kidney problems, thyroid-related problems, and certain medications (8). In most instances, hypertension is a result of some health problem or a consequence of some unhealthy lifestyle habit.

Everyone can develop high blood pressure, but some people are at a higher risk than others. Some risk factors are out of your control, such as:

  • The family history of hypertension
  • Ethnicity and race
  • Aging
  • Gender (being a man)
  • Having a disease (sleep apnea, kidney problems, etc.)

On the other hand, some risk factors associated with hypertension are modifiable. These include:

  • Sedentary lifestyle
  • Smoking and exposure to secondhand smoke
  • Diabetes
  • Overweight and obesity
  • Alcohol consumption
  • High cholesterol
  • Unhealthy diet
  • Eating too much salt
  • Some medications

Phentermine and hypertension

Overweight and obese individuals are at a higher risk of hypertension, so it’s natural to wonder whether weight loss drug could make their blood pressure even worse. Some weight loss medications do increase the risk of hypertension, but when it comes to phentermine that may not be the case. Kim et al. found in their study that while phentermine promoted weight loss and induced adverse reactions in some participants, there were no significant differences in systolic and diastolic blood pressure between control and placebo group (4).

A separate study, published in the Obesity journal, confirmed that phentermine treatment for obesity doesn’t result in increased systolic blood pressure, diastolic blood pressure, and heart rate. Phentermine-assisted weight loss is linked with favorable shifts in blood pressure as well as slowed progression to hypertension in obese individuals (9).

In 2017 one study found that phentermine treatment for weight loss can lower blood pressure, thus making the drug actually helpful for persons with hypertension. Obese adults who were treated with phentermine for six months experienced weight loss and decrease in both diastolic and systolic blood pressure. That being said, blood pressure numbers didn’t improve in persons who had diabetes (10).

While the above-mentioned studies found that phentermine doesn’t aggravate blood pressure, it’s still important to carry out further research on this topic. After all, it’s important to elucidate all the mechanisms of action associated with phentermine in order to uncover whether it could affect blood pressure, particularly in persons with hypertension, in the long run.

So, I can take phentermine with hypertension?

Despite the fact that evidence points out phentermine could be safe for persons with high blood pressure, you should still be cautious. In fact, the best thing to do is to consult your doctor about the problem. Your physician will inform you about the safety of the drug and potential risks that may occur. The doctor may want to monitor you closely if you have high blood pressure and are taking phentermine, but also if you have problems affecting heart valves and reduced kidney function.

Various sources include hypertension or high blood pressure on the list of serious side effects of phentermine (11, 12). Phentermine could lead to pulmonary hypertension, high blood pressure in the arteries of your lungs. Patients who have hypertension or some other cardiovascular problem that could be aggravated by higher blood pressure or accelerated heart rate should take the drug with caution (13).

Always trust your doctor as he or she can evaluate your cardiovascular health and determine whether phentermine is safe for you. If you’ve changed your doctor recently, then make sure you inform them about high blood pressure or some cardiovascular disease you may have before they hand the phentermine prescription.

You should never, under any circumstances, seek for a doctor who will prescribe phentermine if your physician doesn’t do so due to assessment that it could have a negative impact on your blood pressure or some other aspect of health. In other words, while generally, you should be okay when using phentermine with hypertension it doesn’t mean you should avoid consulting doctor and following their instructions or recommendations on the matter.

Phentermine tips you may need to know

Phentermine is not the most frequently prescribed weight loss drug just because of its convenient price, it also works. Getting the most out of phentermine requires following dosage instructions and other orders issued by your doctor. There’s a lot you can do to get the most out of phentermine while minimizing the risk of side effects. Here are a few suggestions you may need to know if you’re considering using phentermine (or you’re already are):

  • Avoid increasing or decreasing dosage on your own. The doctor usually prescribes the lowest dosage first and adjusts it if or when necessary. Taking more than necessary could increase the risk of side effects, overdose, dependence, and other negative effects
  • Take the drug before breakfast or one to two hours after it. Ideally, you should avoid taking phentermine in the late evening because it could make it difficult for you to fall asleep. Remember, phentermine is a stimulant, and it keeps you aware and alert.
  • Exercise regularly and increase physical activity levels in addition to eating a healthier diet and reducing calorie intake. As mentioned above, phentermine is prescribed as a conjunction to lifestyle changes. It works only when you make some modifications in your lifestyle too. That way, you’re equipped to achieve a healthy weight loss and are more likely to maintain weight in healthy range effectively .
  • If the drug impairs your judgment avoid operating heavy machinery or drive when taking it
  • Avoid drinking alcohol when taking phentermine. Alcohol could increase the risk of side effects associated with this drug
  • Never, under any circumstances, should you use phentermine together with other weight loss drugs
  • Your meals should consist of controlled portions of protein, whole grains, and vegetables

Tips to control high blood pressure

Hypertension is a serious problem due to the fact it can contribute to the higher risk of other cardiovascular issues. Fortunately, this is a modifiable problem that you can control with a few wise decisions, such as the following:

  • Lose weight – since being overweight or obese puts you at a higher risk of hypertension the first and the most important thing you can do is to slim down. Start by making some changes in your diet and physical activity levels, stay motivated, and stick to your schedule, and you’ll get there
  • Try to exercise about 150 minutes a week which is about 30 minutes on most days during the week
  • Avoid trans fats and other unhealthy foods and ingredients in favor of fruits, vegetables, whole grains, and other healthy alternatives
  • Decrease salt intake
  • Quit smoking and drinking
  • Reduce caffeine intake
  • Manage stress
  • Get enough sleep


Phentermine is a common weight loss drug that doctors prescribe to their patients whose BMI is 30. Studies show that the drug doesn’t cause high blood pressure, but you should still be cautious and consult your doctor about the subject.