Phentermine and high blood pressure

Phentermine and High Blood Pressure

Phentermine is a weight loss medication that boosts energy levels and reduces appetite to aid weight loss.

However, phentermine will not suit everyone, including some people with hypertension (high blood pressure). In this article, we will look at the link between phentermine and hypertension, and why you must only take this weight loss aid if your doctor has prescribed it.

How Does Phentermine Work?

Phentermine pills are a central nervous system stimulant that may be sold under the brand names Adipex-P and Lomaira in the United States.

The active ingredient is phentermine hydrochloride which stimulates the release of neurotransmitters such as epinephrine. This causes appetite suppression and an increase in energy levels and heart rate. In trials, taking phentermine for 12 weeks led to at least 10% of baseline weight loss in 50% of participants. (1), (2)

However, due to phentermine side effects, and a possible risk of adverse events, these appetite suppressant pills may not suit you if you have uncontrolled or untreated high blood pressure.

What Causes High Blood Pressure?

High blood pressure, or hypertension, is a condition characterized by persistently high pressure within the arteries of the cardiovascular system. In the USA, hypertension is very common, affecting almost half of all adults. (3)

Hypertension is defined as a blood pressure reading of 140/90 or greater. A complex range of environmental, genetic, and physiological factors can increase your risk of developing hypertension, including:

  • Being overweight or obese
  • Lack of physical activity
  • Having a high-salt diet
  • Smoking
  • Excessive alcohol intake
  • Increasing age
  • High-stress levels
  • Poor sleep or sleep apnea
  • Family history of hypertension
  • Specific genetic conditions.

High blood pressure may eventually cause health problems, such as heart disease.

The good news is that some lifestyle modifications are effective in lowering blood pressure. Losing weight, switching to a healthier diet, quitting smoking, becoming more active, and taking steps to mitigate stress and improve sleep could all bring your blood pressure down. (4)

Is There a Link Between Phentermine and High Blood Pressure?

Individuals who are overweight or obese are at greater risk of having high blood pressure.

High blood pressure is known to increase the risk of cardiovascular events such as heart attacks and strokes.

However, concerns have previously been raised that taking phentermine may also increase the risk of cardiovascular events and heart valve disease.

It was hypothesized that phentermine might, therefore, not be a suitable choice for individuals who already have hypertension, as it could theoretically further increase the risk of an adverse event.

However, when scientists tried to answer the question of whether phentermine increased blood pressure, they were surprised by the results.

Several studies have now demonstrated that phentermine treatment for obesity does not increase blood pressure or heart rate. Instead, the weight loss associated with phentermine treatment has been shown to reduce blood pressure. (5) (2)

The caveat to these findings is that to avoid an adverse cardiovascular event, an individual’s blood pressure must be well controlled before they start taking phentermine.

Can You Take Phentermine With High Blood Pressure?

Phentermine is a suitable pharmacological choice for individuals with a BMI of 27 or higher, who also have a weight-related medical condition. This includes those with high blood pressure, as long as it is well controlled.

Uncontrolled blood pressure (blood pressure that remains high or has not yet become consistently normal) is a contraindication for phentermine use. This is because there is a potential risk of adverse cardiovascular events associated with both excess weight and high blood pressure.

If you are wondering what is the highest blood pressure allowed to prescribe phentermine, the answer is that your blood pressure must be consistently lower than 140/90 before the weight loss pills can be prescribed and taken.

Hypertensive individuals who want to take phentermine should therefore take steps to reduce their blood pressure with lifestyle modifications and anti-hypertensive medications. Once their blood pressure is under control, a doctor can prescribe phentermine.


Phentermine is a suitable weight loss medication for individuals who are obese or have a BMI of over 27 with an associated medical condition. This includes those who have controlled hypertension.

Studies of phentermine and blood pressure have shown that by encouraging weight loss, phentermine can further lower an individual’s blood pressure.

However, due to the potential health risks, phentermine must not be prescribed to anyone whose blood pressure has not yet been normalized with medications or lifestyle modification.


Can individuals who have controlled high blood pressure use phentermine?

Many people ask if phentermine is safe for high blood pressure. The answer is that individuals with controlled high blood pressure can use phentermine to aid weight loss. However, your doctor should continue to monitor your blood pressure throughout your treatment with phentermine to check that it is not having an adverse effect.

Can you take phentermine with a high blood pressure medication?

Phentermine can be taken with most medications prescribed to treat high blood pressure. However, you must let your doctor know which medications you take so that they can ensure that phentermine is the right choice for you. Your doctor should also monitor your blood pressure during treatment, as it may become possible to reduce the dose of any antihypertensive medications you take.

Can I take Librax and a blood pressure pill with phentermine?

Taking phentermine and Librax together is not recommended. This is because the combination increases the risk and severity of an abnormally fast heart rate. Your doctor may be able to recommend alternative treatment options. (6)

How much does phentermine raise blood pressure?

In rare cases, phentermine may cause adverse events in which the blood pressure increases. However, numerous studies have shown that phentermine can often help to lower blood pressure due to its positive effect on weight loss. For safety reasons, phentermine should not be prescribed to anyone whose blood pressure has not yet fallen to less than 140/90 despite pharmacological management or lifestyle modification. (5)

How can I lower my blood pressure while taking phentermine?

As phentermine can aid weight loss, taking this pill may subsequently help to lower your blood pressure. Following a healthy diet and exercising regularly is likely to improve further both your blood pressure readings and your progress with weight loss. (4) (5)

What should I do if phentermine causes high blood pressure?

In rare cases, phentermine has been linked to adverse cardiovascular events, including high blood pressure. For this reason, your doctor should monitor your blood pressure and other health indicators while you are taking this medication. If your blood pressure is noted to be increasing, phentermine should be stopped immediately. (7)

Will my blood pressure be lower if I take furosemide with phentermine?

Furosemide is a diuretic anti-hypertensive medication that lowers blood pressure by removing excess fluid in the blood vessels. As weight loss associated with phentermine may also lower blood pressure, this treatment combination may cause a greater reduction in blood pressure than either medication alone. If your blood pressure decreases but remains in the normal range, your doctor may advise you to continue both treatments. However, if your blood pressure becomes abnormally low, they may advise stopping or reducing your dose of furosemide. (8)

Will eating help if my blood pressure feels low when taking phentermine?

If you have symptoms such as light-headedness, breathlessness, weakness, confusion, or irritability, you should not assume that this is due to hunger. Instead, this could be a sign of a severe reaction to phentermine. You must stop taking phentermine and consult a doctor straight away for an emergency assessment.

Can I minimize phentermine blood pressure side effects with CoQ10 or ubiquinone?

Coenzyme Q10, also known as CoQ10 or ubiquinone, is a dietary supplement that has shown some potential to lower blood pressure without side effects. It can be safely taken with phentermine by individuals who want to support healthy blood pressure. However, it should not be used to treat high blood pressure caused by phentermine use. In this situation, the increase in blood pressure should be treated as an adverse health event. You must stop phentermine and seek immediate medical advice. (9)

How long does it take for your blood pressure to go down after taking phentermine?

If phentermine causes an increase in blood pressure, this indicates that it is not a suitable weight loss medication for you. Phentermine concentrations peak within the blood in around 3 to 4 hours, so blood pressure rises are likely to take place within this time frame, too. If your blood pressure rises or you feel unwell when taking phentermine, you must stop taking it immediately and seek medical advice. (10)

Can phentermine cause low blood pressure?

Taking phentermine alone is unlikely to cause clinically low blood pressure. However, if you feel dizzy, tired, weak, nauseous, light-headed, or faint, you must stop taking phentermine and seek advice from your doctor straight away.

Can you take phentermine and topiramate while on blood pressure pills?

Using a combination of phentermine and topiramate (sometimes known by its brand name Qysmia) in addition to antihypertensive medications can increase the risk of low blood pressure. If you take Qysmia with medications for hypertension, your doctor should monitor your blood pressure before, during, and after treatment. If low blood pressure occurs, your doctor may advise reducing your dose of blood pressure pills. (11)


1. (Phentermine).
2. Kim, KK et al. Effects on weight reduction and safety of short-term phentermine administration in Korean obese people. Yonsei Medical Journal. 2006; 47: 614-625.
3. (Hypertension).
4. Oparil S et al. Hypertension. Nature Reviews Disease Primers. 2018; 4: 18014.
5. Hendricks EJ et al. Blood pressure and heart rate effects, weight loss and maintenance during long-term phentermine pharmacotherapy for obesity. Obesity (Silver Spring). 2011; 19(12): 2351-60.
6. (Interactions).
7. (Side Effects).
8. (Furosemide).
9. Rosenfeldt FL et al. Coenzyme Q10 in the treatment of hypertension: a meta-analysis of the clinical trials. Journal of Human Hypertension. 2007; 21: 297-306.
10. (Phentermine Elimination).
11. (Efficacy and Safety).