Phentermine

Weight Management

Phentermine is an appetite suppressant used to help adults lose weight. It is typically prescribed for individuals who have health risks because of their weight and have been unable to lose weight through diet and exercise alone.

Healthcare providers usually consider this medication for patients with:

• Obesity, often defined as a body mass index (BMI) of 30 or higher.
• Overweight status, often defined as a BMI of 27 or higher, when accompanied by weight-related risk factors such as high blood pressure, diabetes, or high cholesterol.

Short-Term Treatment

Phentermine is indicated for short-term use only, typically for a period of a few weeks. It is meant to be used as one part of a comprehensive weight-loss plan that includes:

• A reduced-calorie diet.
• Regular physical activity.
• Behavioral changes to support lifestyle goals.

The medication works by decreasing appetite, which helps patients consume fewer calories. It is not intended for long-term use or for individuals who want to lose a small amount of weight for cosmetic reasons.

Mechanism of Action

Phentermine belongs to a class of medications known as anorexiants or appetite suppressants. It is chemically similar to amphetamines and works by acting on the central nervous system.

The exact way phentermine helps with weight loss is not completely understood. However, it is believed to work by:

• Stimulating the hypothalamus, the part of the brain that controls appetite.
• Increasing the release of certain chemicals, such as norepinephrine, which signal the body to feel less hungry.
• Helping the body feel full or satisfied more quickly.

By reducing the urge to eat, phentermine makes it easier for individuals to stick to a low-calorie diet. It is intended for short-term use as an addition to exercise and healthy eating habits.

Common Side Effects

Many people experience mild side effects while taking phentermine. These commonly include:

• Dry mouth or an unpleasant taste
• Constipation, diarrhea, or vomiting
• Difficulty sleeping (insomnia)
• Nervousness, restlessness, or tremors
• Dizziness and headache
• Changes in sexual desire or impotence

Serious Side Effects

Some side effects can be severe. Seek medical attention immediately if you experience:

• Chest pain or heart palpitations
• Shortness of breath, especially during activity
• Swelling of the legs and ankles
• Fainting or extreme dizziness
• Blurred vision
• Severe headache
• Significant mood changes or irritability

In rare cases, phentermine has been associated with serious heart valve problems or high blood pressure in the lungs. Contact your doctor immediately if you have trouble breathing or experience a decreased ability to exercise.

Heart and Lung Risks

Serious heart and lung conditions have been associated with the use of phentermine. Primary pulmonary hypertension (PPH), a rare but potentially fatal lung disease, has been reported. Symptoms may include chest pain, shortness of breath during exertion, or fainting. Serious heart valve problems have also been reported, especially when phentermine is used in combination with other weight loss drugs.

Contraindications

Phentermine is not suitable for everyone. It is generally avoided in individuals with the following conditions:

• History of heart disease, including stroke, heart failure, or irregular heartbeat.
• Uncontrolled high blood pressure.
• Glaucoma.
• Hyperthyroidism (overactive thyroid).
• A history of drug or alcohol misuse.
• Agitated states or severe anxiety.

The medication should not be used during pregnancy or while breastfeeding. It is also contraindicated for use within 14 days of taking monoamine oxidase inhibitors (MAOIs).

Tolerance and Misuse

Phentermine is a controlled substance because it is chemically similar to amphetamines and carries a risk of dependency or misuse. Tolerance to the appetite-suppressing effects usually develops within a few weeks. If the medication stops working effectively for weight loss, the dosage is typically not increased; instead, the drug is usually discontinued.

Other Precautions

• Monitoring: Regular checks of blood pressure and heart rate are often recommended, as phentermine can cause these levels to rise.
• Impairment: The drug may cause dizziness or blurred vision, which can interfere with the ability to drive or operate machinery safely.
• Diabetes: Weight loss and the effects of phentermine may change blood sugar levels, potentially requiring adjustments to diabetes medications.
• Alcohol: Using alcohol while taking phentermine may increase the risk of adverse side effects.

Pregnancy

Phentermine should not be used during pregnancy. Weight loss offers no potential benefit to a pregnant person and may result in fetal harm. Medical guidelines typically recommend a minimum weight gain for all pregnant individuals, including those who are already overweight or obese, to support the development of the fetus.

If you are pregnant or planning to become pregnant, discuss weight management and nutrition with a healthcare professional. If you discover you are pregnant while taking this medication, it is important to notify your doctor immediately.

Breastfeeding

It is not known if phentermine passes into human breast milk. Because many drugs are excreted in milk and there is a potential for serious adverse reactions in nursing infants, healthcare providers generally recommend either stopping the medication or avoiding breastfeeding while using phentermine.

Consult with a healthcare provider to discuss the risks and benefits of using this medication if you are planning to breastfeed or are currently nursing.

Oral Formulations

Phentermine is available in several oral dosage forms to accommodate different patient needs. These include:

• Tablets: Conventional tablets intended to be swallowed.
• Capsules: Standard capsules and extended-release capsules.
• Orally Disintegrating Tablets: These tablets are placed on the tongue until they dissolve and can be swallowed with or without water.

FDA Approval and Indications

Phentermine was first approved by the U.S. Food and Drug Administration (FDA) in 1959. It is currently approved for short-term use, typically defined as up to 12 weeks, as an adjunct to a regimen of weight reduction based on exercise, behavioral modification, and caloric restriction.

The medication is indicated for patients with an initial body mass index (BMI) of:

• 30 kg/m2 or greater (obese)
• 27 kg/m2 or greater (overweight) in the presence of other risk factors, such as controlled hypertension, diabetes, or hyperlipidemia.

Controlled Substance Status

Phentermine is classified by the Drug Enforcement Administration (DEA) as a Schedule IV controlled substance. This classification is due to its chemical similarity to amphetamines, which carries a risk for misuse, abuse, and physical or psychological dependence. Because of these risks, its use is strictly regulated and limited to short durations.

Regulatory History and Safety

In the late 1990s, phentermine was frequently prescribed in combination with fenfluramine or dexfenfluramine, a combination commonly known as Fen-Phen. While the FDA requested the withdrawal of fenfluramine and dexfenfluramine from the market in 1997 due to reports of heart valve disease, phentermine remained FDA-approved and available for use as a standalone treatment.

Current regulatory labeling includes warnings regarding the risk of primary pulmonary hypertension and valvular heart disease, although these were more strongly associated with the combination therapies. The FDA requires that phentermine be used only for short-term management and not in combination with other weight-loss drugs unless specifically approved for such use.

Role in Weight Management

Phentermine is an appetite suppressant that belongs to a class of medications called anorexiants. It works by stimulating the central nervous system to decrease appetite. Because it is chemically related to amphetamines, it is classified as a controlled substance.

Who It Is For

Healthcare providers typically prescribe phentermine for adults who have significant health risks due to their weight. This includes:

• People with a body mass index (BMI) of 30 or higher (obesity).
• People with a BMI of 27 or higher (overweight) who also have weight-related medical conditions such as high blood pressure, diabetes, or high cholesterol.

Short-Term Use

Phentermine is approved only for short-term use, usually up to 12 weeks. It is not intended for long-term weight maintenance because its effects may wear off after several weeks as the body builds a tolerance. Additionally, because of the potential for misuse or dependency, long-term use is generally avoided.

Maximizing Effectiveness

Weight loss results are most effective when phentermine is combined with lifestyle modifications. These include:

• Following a low-calorie or reduced-calorie diet.
• Engaging in regular physical activity.
• Implementing behavioral changes to support healthy habits.

If significant weight loss is not achieved within the first few weeks of treatment, a healthcare provider may decide to discontinue the medication, as increasing the dose does not usually improve results and may increase the risk of side effects.