Phentermine is a prescription medication commonly used to aid weight loss by suppressing appetite. It is often prescribed to individuals who are overweight or obese and have struggled to lose weight through diet and exercise alone. However, Phentermine is not suitable for everyone. This article outlines the groups of people who should avoid using Phentermine due to potential health risks and complications.

Individuals with a History of Cardiovascular Disease

Phentermine can significantly increase heart rate and blood pressure, posing serious risks to individuals with a history of cardiovascular disease. This includes:

  • Heart Disease: Individuals with any form of heart disease, such as coronary artery disease or heart rhythm disorders, should avoid Phentermine. The increased heart rate and blood pressure can worsen these conditions.

  • Heart Rhythm Disorders: Phentermine can cause irregular heartbeats (arrhythmias), which are particularly dangerous for those with existing heart rhythm issues.

  • Coronary Artery Disease: This condition involves narrowed or blocked arteries, and Phentermine’s increased demand on the heart can lead to severe complications.

  • Congestive Heart Failure: The medication can increase fluid retention and blood pressure, exacerbating heart failure symptoms.

  • Stroke History: For those who have had a stroke, the elevated blood pressure caused by Phentermine use can increase the risk of another stroke.

People with Uncontrolled High Blood Pressure

Phentermine can exacerbate high blood pressure (hypertension). For individuals with uncontrolled hypertension, using Phentermine is particularly risky. Even those with controlled hypertension need close monitoring, but those with uncontrolled hypertension should avoid it to prevent complications like stroke, heart attack, and kidney damage.

Those with Hyperthyroidism

Hyperthyroidism, a condition where the thyroid is overactive, can be worsened by Phentermine. The medication can further elevate thyroid hormone levels, leading to:

  • Increased Metabolic Rate: This can cause symptoms such as rapid heartbeat, sweating, nervousness, and weight loss.

  • Serious Health Issues: If unmanaged, hyperthyroidism can lead to severe health problems like heart issues and brittle bones.

Individuals with hyperthyroidism should avoid Phentermine to prevent worsening their condition.

Individuals with Glaucoma

Glaucoma is characterized by increased pressure in the eye, which can damage the optic nerve and lead to vision loss. Phentermine can raise intraocular pressure, posing a significant risk to individuals with glaucoma. The increased pressure can speed up the progression of glaucoma and heighten the risk of permanent vision loss.

Pregnant or Breastfeeding Women

The safety of Phentermine during pregnancy and breastfeeding is not well-established. Due to the potential risks to the fetus or infant, it is generally recommended that women avoid Phentermine during these periods. Potential risks include:

  • Birth Defects: There is concern that Phentermine could harm a developing fetus.

  • Breastfeeding Complications: The medication might pass to the infant through breast milk, potentially causing adverse effects.

Individuals with a History of Drug Abuse or Dependence

Phentermine is a stimulant with potential for abuse or dependence. It is chemically similar to amphetamines, known for their high addiction potential. Individuals with a history of substance abuse, including alcohol, nicotine, or other drugs, should avoid Phentermine due to the risk of developing a new addiction or triggering a relapse.

People with Certain Psychiatric Conditions

Phentermine can impact mood and mental health, making it unsuitable for individuals with certain psychiatric conditions, such as:

  • Anxiety Disorders: Phentermine can increase anxiety symptoms and cause agitation.

  • Bipolar Disorder: It can trigger manic or depressive episodes.

  • Schizophrenia: The stimulant effects can worsen symptoms like hallucinations or delusions.

  • Other Psychiatric Conditions: Any condition affecting mood or mental stability can be worsened by Phentermine.

Individuals Taking Certain Medications

Phentermine can interact with various medications, leading to potentially dangerous side effects. It is crucial to inform your healthcare provider about all medications you are taking to avoid potential interactions. Important medications to be aware of include:

  • Monoamine Oxidase Inhibitors (MAOIs): Used to treat depression, these can cause severe interactions with Phentermine.

  • Selective Serotonin Reuptake Inhibitors (SSRIs): Commonly prescribed for depression and anxiety, SSRIs can interact with Phentermine, increasing the risk of serotonin syndrome, a potentially life-threatening condition.

  • Other Appetite Suppressants: Combining Phentermine with other appetite suppressants can heighten the risk of cardiovascular side effects and other complications.

Additional Conditions to Consider

In addition to the major categories listed, other conditions and situations warrant avoiding Phentermine. These include:

  • Severe Headaches: Phentermine can worsen headache symptoms.

  • Chest Pain: Any history of chest pain can be exacerbated by the medication.

  • Liver Disease: Phentermine can affect liver function, potentially worsening liver conditions.

  • Extreme Agitation or Nervousness: The stimulant nature of Phentermine can increase these symptoms.

  • Allergies to Phentermine: Any known allergy to the medication or its components is a clear contraindication.


While Phentermine can be an effective weight loss aid for some, it is not suitable for everyone. Individuals with a history of cardiovascular disease, uncontrolled high blood pressure, hyperthyroidism, glaucoma, or psychiatric conditions should avoid Phentermine. Pregnant or breastfeeding women, those with a history of substance abuse, and individuals taking certain medications should also avoid this medication.

Before starting Phentermine, it is crucial to discuss your complete medical history with your healthcare provider, including any conditions, medications, and history of substance abuse. Your healthcare provider can help determine if Phentermine is a safe and appropriate option for you.

For those who cannot take Phentermine, alternative weight loss strategies are available, including lifestyle changes, other medications, and surgical options. Always consult with a healthcare professional to find the most suitable and safe weight loss plan for your individual needs.

Who Should Avoid Phentermine?