What is phentermine?
​
Phentermine is one of the most popular weight loss drugs in the world.
Phentermine is an FDA-approved drug intended for weight loss. Its chemical structure is similar to amphetamine,
Phentermine is used with a doctor-approved well-balanced, reduced-calorie diet and exercise to help you lose weight. It is used by certain overweight people, such as those who are obese or have weight-related medical problems. Losing weight and keeping it off can lessen the many health risks that come with obesity, including heart disease, diabetes, high blood pressure, and a shorter life.
It may also be prescribed if you’re overweight with a BMI greater than or equal to 27 and have at least one weight-related condition, such as high blood pressure, high cholesterol, or type 2 diabetes.
​
How Does It Work?
Phentermine belongs to a class of drugs called “anorectics,” also known as appetite suppressants.
Taking phentermine helps suppress your appetite, thereby limiting how many calories you eat. Over time, this can lead to weight loss. It also increases the amount of energy used by your body.
While the exact mechanisms behind the appetite-reducing effects of phentermine remain unclear, the drug is thought to act by increasing neurotransmitter levels in your brain.
Neurotransmitters are your body’s chemical messengers and include norepinephrine, serotonin, and dopamine.
When your levels of these three chemicals increase, your feeling of hunger decreases.
Effective for Weight Loss
Several clinical studies have proven that phentermine can boost fat loss.
The expected average weight loss with phentermine use is 5% of your initial body weight. Yet, over 12 weeks, it can be as high as 10%. This equates to a weight loss of 10–20 pounds (4.5–9 kg) for a 200 pound (90.7 kg) person.
In a meta-analysis of six studies, people who took the average dose of 27.5 mg of phentermine for 13 weeks lost an average of 13.9 pounds (6.3 kg) compared to 6.2 pounds (2.8 kg) in placebo groups.
In users, this weight loss has translated to a significant decrease in waist circumference, improved insulin sensitivity, and blood sugar control, as well as favorable effects on triglyceride and cholesterol levels.
Side Effects and Precautions
The most commonly reported side effects include:
-
Dry mouth
-
Sleeping problems
-
Dizziness
-
Heart palpitations
-
Flushing of the skin
-
Fatigue
-
Constipation
-
Irritability
You shouldn’t take phentermine if you have heart disease, hyperthyroidism, glaucoma, or if you’re pregnant or nursing.
Phentermine should also not be prescribed in combination with monoamine oxidase inhibitors (MAOIs), a class of medications used to treat depression.
While there are common side effects associated with the use of phentermine, it’s tolerated by most people. However, people with certain conditions and women who are pregnant or nursing should not use phentermine.
Healthy Ways to Promote and Maintain Weight Loss
While phentermine can be a powerful weight loss aid, the only proven way to shed weight — and to keep it off in the long term — is cultivating healthy lifestyle behaviors.
Without making the proper changes, it is likely that you’ll gain back the weight you lost — and possibly more — once you stop taking phentermine.
A comprehensive lifestyle change includes:
​
-
A reduced-calorie diet: If you have excess weight to lose, eat 300–500 fewer calories per day. A registered dietitian can help you tailor this range based on your preferences and goals.
-
Prioritize nutrient-dense foods: Nutrient-dense foods — such as fruits and vegetables — are relatively low in calories and high in nutrients, such as fiber, vitamins, and minerals.
-
Increase physical activity: Guidelines recommend a minimum of 150 minutes per week of moderate aerobic exercise, such as brisk walking or running.
-
Behavioral strategies: Behavior changes includes regular self-monitoring of food intake, physical activity, and your weight, plus making adjustments as needed.
Making these lifestyle changes can be difficult and shouldn’t happen all at once. It will take an investment of your time and energy — but the outcome will be long-term weight loss and overall better health.
Lifestyle and behavioral modification are the cornerstones of successful weight loss and maintenance.
​
​
​
​
​