Taking Phentermine Safely
Supplementing Phentermine with Diet and Exercise
Health and Safety Information
Article Summary
Questions & Answers
Related Articles

This article was co-authored by

Mark Ziats, MD, PhD

. Dr. Ziats is an Internal Medicine Physician, Researcher, and Entrepreneur in biotechnology. He received his PhD in Genetics from the University of Cambridge in 2014, and completed his MD shortly thereafter, at Baylor College of Medicine in 2015.

There are 28 references cited in this article, which can be found at the bottom of the page.

Over 1.9 billion people are overweight, and of those 1.9 billion, at least 600 million people are obese.[1] 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] 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]

Part 1

Taking Phentermine Safely

  1. Image titled Lose Weight with Phentermine Step 1


    Attempt diet and exercise first.

    Because of the risks of phentermine, this drug should be used only after




    changes have been proven ineffective.


    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. Image titled Lose Weight with Phentermine Step 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.


    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] 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] Patients over the age of 65 also should not take phentermine.[8]
    • 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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    Consider the risks carefully.

    In addition to potential side effects, phentermine can also be habit-forming in some patients.


    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] 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.


    Because phentermine is a stimulant, it is generally best to take it in the mornings so that it doesn’t interfere with sleep.


    Be sure that you follow your doctor’s and pharmacist’s instructions carefully. Never exceed the recommended dosage or “double-up” on your phentermine.


    • Taking phentermine at the same time every morning can help you remember to take it. Try to maintain a consistent schedule.[15]
    • 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.


    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.

  6. Image titled Lose Weight with Phentermine Step 6


    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.


    • 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]
    • 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]
    • 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

Supplementing Phentermine with Diet and Exercise

  1. Image titled Lose Weight with Phentermine Step 8


    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. Image titled Lose Weight with Phentermine Step 9


    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.


    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]
    • A very-low-calorie diet, often taken in liquid form, under close supervision[24]
    • 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. Image titled Lose Weight with Phentermine Step 10


    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. Image titled Lose Weight with Phentermine Step 11


    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.[25]

  5. Image titled Lose Weight with Phentermine Step 12


    Talk to a behavioral specialist.

    Behavioral therapy is an integral part of medical weight-loss programs.


    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

Community Q&A

Add New Question

  • Question

    I take phentermine at 7 AM, but by 2 PM I start to feel hungry. What can I do?

    Eat a small amount of protein (like turkey lunchmeat) as a snack and drink lots of water.

  • Question

    How do I lose weight using phentermine correctly?

    First, always consult with your physician. Take phentermine in the morning – no later than 9 a.m.. And, you need to dedicate time every day to exercising and keeping a record of what you are eating, making note of your calories, sodium, sugar. Sodium and sugar are not good when you are trying to loose weight. Additionally, take a good complete vitamin.

  • Question

    Why should I not eat at the same time I take phentermine?

    It is best to allow the medication to reach the gut before food is introduced. Breakfast foods that are high in fiber slow digestion, which interferes with the absorption of the timed release tablets. Also, if you consume soy products (as an alternative protein), the soy has enzyme inhibitors and other substances that can block the uptake of certain essential minerals and possibly medications.

  • Question

    It controls my appetite until almost bed time, but then I feel my appetite to come back at bed time. What can I do to not want to eat all through the night?

    Have a high protein snack a couple hours before bed and drink a glass of water.

  • Question

    Why is this not recommended for over age 65?

    Most likely because of increased risk of blood pressure and heart problems. Any preexisting issues can interact adversely with the drug as well. Examples are diabetes, high blood pressure heart pain.

  • Question

    When I first took Phentermine I noticed that it did help with cravings, but three days in, the cravings are back! Why?

    You must drink plenty of water with this medication. Also, take it at the same time every day. Eat plenty of protein and fiber rich foods and get plenty of exercise. Also, make sure you’re getting 8 hours of sleep nightly. Sometimes thirst or lack of sleep can cause food cravings.

  • Question

    Can I eat oatmeal with Phentermine?

    Yes! The fiber in oatmeal will help fill you up for hours, which will help you with your weight loss goals.

  • Question

    I have some phentermine that has an expired date, can I still take them?

    No, you should not take any medication that has an expired date.

  • Question

    When can I eat after taking phentermine in the morning?

    Angel Davis

    Community Answer

    I take Phentermine every morning at 6:30 before I start work. I’ll normally eat right before or right after I take the medicine. If you wait to eat a few hours after you take your medicine, you may not even want to eat anything because you possibly won’t be hungry by the time you eat. And another thing is that you’ll have to force yourself to eat sometimes. An example is like yesterday, I took my medicine at 6:30 before work and right after taking it I ate a hand full of gummies that I bought out of the vending machine. I didn’t eat anything else until I got home at 6:00 in the afternoon and all I ate was 2 corn-dogs. So literally all I ate yesterday was a pack of gummies and 2 corn-dogs.

  • Question

    Can I take the medicine at night?

    No, it is not a good idea to take this medication at night because it will cause insomnia.

Show more answers

Unanswered Questions

  • How many calories, and how much sodium and sugar can a 54 year old woman who weighs 180 pounds have each day while taking Phentermine?

  • How long will the headaches and diarrhea last when losing weight with Phentermine?

  • Is phentermine safe to take with other medications?

  • When should I use Phentermine?

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  • Surround yourself with supportive people who will inspire you to continue your medical weight-loss program in a safe, healthy, and happy way.
  • Do not expect to lose all the weight right away. Effective weight loss tends to be slow and steady. Crash diets and fads often cause the weight to bounce right back. Focus on long-term health, not short-term weight loss.
  • The average patient on phentermine loses about 5% of his body weight. While this seems small, this amount of weight loss can have huge health benefits, such as reduced risk for diabetes and heart disease.[27]
  • To achieve success you should eat right, less, exercise more and change your lifestyle. An appetite suppressant will not work by itself to allow you to lose weight.


  • 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.
  • 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.
  • 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.
  • 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.
  • 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.[28]

Article SummaryX

Before trying to lose weight with the appetite suppressant Phentermine, talk to your doctor about the associated risks, including increased blood pressure and chest pain. If you and your doctor agree that Phentermine is right for you, begin taking it in the morning since it’s a stimulant that can interfere with sleep. Plan to take Phentermine for no more than 6 weeks, since it can be habit-forming in some patients. During those weeks, be on the lookout for side-effects, like vomiting, diarrhea, dizziness, tremors, or swollen legs. If you notice any of these symptoms, stop using Phentermine immediately and notify your doctor. For more tips from our Medical co-author, including how to supplement Phentermine with diet and exercise, keep reading!

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Article Info

This article was co-authored by Mark Ziats, MD, PhD. Dr. Ziats is an Internal Medicine Physician, Researcher, and Entrepreneur in biotechnology. He received his PhD in Genetics from the University of Cambridge in 2014, and completed his MD shortly thereafter, at Baylor College of Medicine in 2015.

Categories: Losing Weight

In other languages:

Español: bajar de peso con fentermina, Italiano: Perdere Peso con la Fentermina, Deutsch: Mit Phentermine abnehmen, Русский: похудеть с помощью Фентермина, Français: perdre du poids avec de la phentermine, Bahasa Indonesia: Menurunkan Berat Badan dengan Phentermine, Nederlands: Gewicht verliezen met phentermine, العربية: خسارة الوزن باستخدام الفينتيرمين, 中文: 使用芬特明减肥

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