How to Lose Weight with Phentermine

Medically reviewed by Mark Ziats, MD, PhD

Last Updated: April 8, 2021 References Approved

Over 1.9 billion people are overweight, and of those 1.9 billion, at least 600 million people are obese.^{[1]
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Trustworthy Source
World Health Organization
Health information and news provided by the World Health Organization
Go to source} Even though obesity can be tied to a variety of health problems such as heart disease, cancer, and diabetes, it can be difficult for overweight and obese people to lose the extra weight. In these cases, an appetite suppressant such as phentermine can help with initial, short-term weight loss.^{[2]
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Research source} Phentermine should not be used by those who wish to shed a few pounds for cosmetic purposes: only those struggling with obesity should use this drug.^{[3]
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Mayo Clinic
Educational website from one of the world's leading hospitals
Go to source}

Part 1

Part 1 of 2:

Taking Phentermine Safely

1
Attempt diet and exercise first. Because of the risks of phentermine, this drug should be used only after dietary and exercise changes have been proven ineffective.^{[4]
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Trustworthy Source
Mayo Clinic
Educational website from one of the world's leading hospitals
Go to source} Before seeking a phentermine prescription, make lifestyle adjustments to try to lose extra weight. Be sure to consult a physician before making any major changes to your diet and exercise routine to ensure that you remain safe and healthy. Some changes you might make include:
- Take a 30-minute walk every morning
- Take the stairs instead of the elevator at work or at home
- Replace sugary drinks like soda or energy drinks with water
- Replace processed snacks (such as potato chips) with fresh fruits, vegetables, and nuts
- Drink a glass of water with every meal to help you feel full and satisfied
- Eat foods with lots of fiber such as whole grains
- Do 15 minutes of moderately aerobic exercise each day, such as jogging, biking, or swimming
2
Ask your physician if a phentermine prescription is right for you. If it is medically necessary for you to lose weight (and if diet and exercise aren't working), talk to your doctor about whether your weight loss might be assisted with the use of an appetite suppressant. Phentermine can help patients feel full for longer and resist eating unnecessary calories.^{[5]
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Mayo Clinic
Educational website from one of the world's leading hospitals
Go to source} Phentermine is not a magic weight loss drug: it does not work for all patients, and there are a number of risks associated with this medicine.
- Furthermore, phentermine by itself will not help you lose weight, it will only decrease the apatite. It will still require self discipline to eat healthy and not overeat and to exercise in order to lose weight.
- While many of the side effects are minor, others can be quite severe (such as increased blood pressure and chest pain).^{[6]
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  Research source} Never self-prescribe phentermine or try to obtain it illegally. Only take this medication under a doctor's care.
- Phentermine should not be used by patients with high blood pressure, cardiovascular disease, glaucoma, hyperthyroidism, substance abuse issues, or by women who are pregnant or might become pregnant or breastfeeding.^{[7]
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  Research source} Patients over the age of 65 also should not take phentermine.^{[8]
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- Phentermine can react negatively to other medications such as MAO inhibitors, SSRIs, and weight loss drugs. Talk to your doctor about all medications, supplements, and herbs you take to make sure that you don't experience harmful side effects.^{[9]
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3
Consider the risks carefully. In addition to potential side effects, phentermine can also be habit-forming in some patients.^{[10]
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Research source} If your health requires you to lose weight, these potential side effects might be worth the risk; however, talk to your doctor about the dangers of phentermine as well as the benefits you might experience.
- There have been reports of doctors prescribing phentermine unsafely and without proper monitoring. Be sure that your doctor is reputable and forthright about the risks of phentermine before you begin taking the drug.^{[11]
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  Research source} You can do some quick research on your doctor by looking on your state's medical licensing website to find the doctor's name and credentials.
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Take phentermine once every morning. Most phentermine prescriptions involve a capsule or tablet taken orally once a day.^{[12]
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Research source} Because phentermine is a stimulant, it is generally best to take it in the mornings so that it doesn't interfere with sleep.^{[13]
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Research source} Be sure that you follow your doctor's and pharmacist's instructions carefully. Never exceed the recommended dosage or "double-up" on your phentermine.^{[14]
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- Taking phentermine at the same time every morning can help you remember to take it. Try to maintain a consistent schedule.^{[15]
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- If you were prescribed time-release capsules, be sure to swallow them whole. Chewing a time-release capsule can lead to incorrect dosages and side effects.^{[16]
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Take phentermine for three to six weeks. Phentermine is designed for short-term use, not for permanent or long-term use. Most patients are on the drug for three to six weeks as a way to jump-start a weight-loss program.^{[17]
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Research source} Your doctor will be monitoring you throughout this time to ensure that you are responding appropriately to the drug and that you are not experiencing side effects.
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Be on the lookout for side effects. It is important that phentermine patients be aware of side effects. Pay attention to your body as you take the drug, and notify your doctor of any sudden changes that you notice. While some side effects are only minor and inconvenient, other side effects are dangerous and require immediate medical attention.^{[18]
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- Minor to moderate side effects include dry mouth, constipation, vomiting, and diarrhea. You should notify your physician if these side effects are severe and long-lasting.^{[19]
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- Serious side effects include heart palpitations, high blood pressure, insomnia, dizziness, tremors, chest pain, breathlessness, and swollen legs. Notify your doctor immediately at the first sign of these side effects.^{[20]
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- Sometimes phentermine can enhance the effects of alcohol. Do not drive or use heavy machinery until you know how phentermine affects you, and it is a good idea to stay away from alcoholic beverages while on the drug.^{[21]
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Store the medicine safely. Phentermine should be stored in a cool, dry, dark place. It is best not to store phentermine in the bathroom as it can become warm and moist when you bathe or shower. Make sure that phentermine is not in the reach of any children (such as in a childproofed drawer) in order to keep them safe.

Part 2

Part 2 of 2:

Supplementing Phentermine with Diet and Exercise

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Recognize that phentermine requires diet and exercise to work. Phentermine's effects tend to plateau over time, and many patients develop a resistance to the drug. This is why it is essential that you get on a stable, sustainable diet and exercise plan, even while taking the drug. A healthy diet and regular exercise can allow you to maintain your weight loss or perhaps even continue to lose weight. Phentermine will help you lose weight in those crucial first few weeks, but only diet and exercise will give you long-term success in your weight-loss journey.
2
Consult a dietitian about a safe diet plan. A licensed dietitian can help you adjust your diet in a way that is both safe and effective for weight loss. Ideally, your dietitian will also be able to monitor your progress to ensure that you are responding well to your new weight-loss regime.^{[22]
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Research source} Every patient will require a different plan; however, some common weight-loss strategies include:
- Meal replacements (especially for patients who struggle with portion control)^{[23]
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- A very-low-calorie diet, often taken in liquid form, under close supervision^{[24]
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- Lifestyle modification. This can include rather simple changes such as avoiding processed snack foods, eating lots of low-fat proteins and fresh fruits and veggies, and steering clear of alcohol, simple carbohydrates, and sugars.
3
Measure your calorie intake carefully. Make sure that you are sticking to your diet plan by keeping track of the calories you consume. Make a list of all the food you eat throughout the day. Using a simple online tool or phone app, you can calculate your daily calories intake. Confirm that your daily calories fit within the diet plan worked out by your dietitian and physician.
- A food journal (using an app, a website, or just pen and paper) might also be useful. By recording everything you eat, you can learn to resist temptations more readily.
4
Create an exercise plan with your physician. Depending on your current weight and health, there are some exercises that might be safer for you to perform than others. Talk with your doctor about some of the best ways for you to integrate exercise into your life in a healthy way. Ideally your exercise plan will allow you to continue losing weight even after you discontinue your use of phentermine.
- If you cannot exercise strenuously right away, consider low-impact exercise such as swimming, or even walking. You can always work your way up to more strenuous exercises such as running, jogging, or lifting weights.
5
Talk to a behavioral specialist. Behavioral therapy is an integral part of medical weight-loss programs.^{[25]
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Research source} A behavioral specialist can help you stick to your diet and exercise goals. Perhaps you get tempted to eat because of television commercials, or perhaps you overeat when you are stressed out. A behavioral specialist will use cognitive behavioral therapy to retrain your mind to respond to stress and temptation in healthier, more positive ways. This will help you lose weight while on phentermine as well as after you stop taking the appetite suppressant.

Health and Safety Information

Questions to Ask Your Doctor about Taking Phentermine

Phentermine Side Effects

Phentermine Precautions and Interactions

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Warnings

Avoid alcohol while taking phentermine, as it may make side effects worse. Those with substance abuse issues should avoid phentermine since it can be an addictive substance.

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Do not use phentermine during pregnancy as it may hurt your unborn baby. You should also avoid it when breastfeeding or if you think you might become pregnant.

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Phentermine should be used for only a few weeks to avoid addiction. Do not take this medication for long periods of time — usually three to six weeks is the proper timeline.

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Be aware of side effects and negative drug interactions. Phentermine may have multiple side effects. These are exacerbated if you take an incorrect dose or combine it with other medications. Drug interaction is very dangerous and may cause life-threatening conditions such as high blood pressure and tremors.

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Multiple companies offer generic forms of phentermine without prescription. Prices may be lower, but those pills may be ineffective and even dangerous. Please make sure you are buying a certified medicine from an FDA-approved manufacturer to reduce the risk of side effects.^{[26]
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