When Should I Take My Phentermine

When Should I Take My Phentermine?

In order to maximize the weight loss potential of your phentermine prescription, you should always follow the instructions given to you by your phentermine doctor.

Still, sometimes it can be confusing if things weren’t made clear when you picked up your prescription, and you’re left thinking: When should I take my phentermine?

Here, we’ll explain everything you need to know in this step-by-step guide about how and when to take your phentermine and what to avoid while taking this medication.

Before You Take Phentermine

It is essential to clarify that phentermine is not suitable for everyone.

First and foremost, you must not take phentermine if you are pregnant, as it can harm an unborn baby.

You should also not take it if you are breastfeeding, as it can be passed into breast milk and may harm a nursing baby.

You should not take phentermine if you have a history of heart disease, severe or uncontrolled blood pressure, overactive thyroid, glaucoma, a history of pulmonary hypertension, or if you have a history of drug or alcohol abuse.

You should also not take phentermine if you have taken an MAO inhibitor (e.g., isocarboxazid, linezolid, or tranylcypromine) in the past 14 days, given that a dangerous drug interaction could occur.

Lastly, you should not take phentermine if you are allergic to it or if you have had an allergic reaction to other diet pills, amphetamines, stimulants, or cold medications.

Once you arrive at the appointment to be evaluated for phentermine, tell your doctor if you have any of the following: high blood pressure, diabetes, kidney disease, a thyroid disorder, or an aspirin allergy.

It is vital to disclose all of your medical histories, even if you think it is unrelated. It is crucial for your safety that your doctor is properly informed of any potential there may be for an adverse reaction to the medication.

When to Take Phentermine

If your doctor decides you are suitable for a phentermine prescription, he or she should provide clear instructions for when to take it.

In general, phentermine should be taken at the beginning of the day and normally on an empty stomach. Some brands of phentermine should be taken between half an hour and an hour before breakfast, while others are taken within two hours of eating your first meal.

These instructions will vary with different phentermine pills.

If you’re taking a smaller dose (or splitting tablets), you will take your phentermine up to three times per day. Just remember: never exceed the maximum dosage of 37.5mg per day.

Given the many possible variations in when and how to take phentermine, always take phentermine precisely as prescribed by your doctor and follow all directions listed on your prescription label.

Phentermine is a stimulant that can cause insomnia, so you shouldn’t take this medication until 6 pm.

If you take phentermine late at night, you could experience problems sleeping. That being said, if you have a different waking schedule (such as if you work nights or shifts), you may need to adjust when you take phentermine.

You should explain any relevant schedule concerns to your doctor a the initial appointment so that he or she can devise a suitable phentermine schedule for you.

If you miss a dose, you should take the dose as soon as you remember. However, if it is almost time for your next dose, then it is better to skip the missed dose. You should NEVER take extra medicine to make up for the missed dose.

How to Take Phentermine

How to Take Phentermine

Phentermine can be prescribed in tablet, capsule, or ODT (orally disintegrating/dissolving tablet) form. Available doses range from 8 to 37.5mg, taken 1-3 times daily.

To give you an idea of the possibilities: Adipex-P is a 37.5mg tablet or capsule taken once per day, while Lomaira is an 8mg tablet taken up to three times per day, and Suprenza is an ODT taken once per day.

Your individual phentermine dosage will be determined by your doctor according to your specific needs and requirements.

Phentermine should never be taken in larger or smaller amounts, more or less often, or for longer periods than prescribed.

Always consult your doctor if you think the medication isn’t working correctly and want to adjust your dose, as taking more than your recommended phentermine dosage can cause severe and life-threatening side effects.

Common phentermine side effects include dry mouth, changes in taste, hyperactivity or restlessness, insomnia, diarrhea, constipation, headaches, dizziness, and nausea, amongst others.

However, if you feel that the dosage is too strong for you or if you experience any symptoms of severe side effects, contact your doctor immediately.

You should also not stop taking phentermine suddenly, or you could experience unpleasant withdrawal symptoms. Ask your doctor how to safely stop using this medicine if you do decide you want to stop taking it before the end of your prescription.

What to Avoid on Phentermine

Drinking alcohol can increase the incidence or severity of specific side effects, so you should avoid alcohol while taking phentermine.

Phentermine may also impair your thinking or reactions, so be careful if you drive, operate heavy machinery, or do anything which requires you to be alert.

During the first few days of phentermine, it’s advisable to monitor how you feel to self-assess how the medication affects your body. If you feel uncertain about taking on specific tasks, seek advice from your doctor.

In your first consultation, you should tell your doctor about any medications or supplements that you are currently taking, even if they are non-prescription.

Many medications or supplements interact with the phentermine and could cause the medication to be less effective or even prove dangerous.

Your doctor may recommend that you take additional vitamins or supplements with phentermine. Still, if not, you should check with your doctor before you decide to take any additional products yourself.

You should also tell your doctor about any medications you start or stop using during your treatment with phentermine, especially antidepressants.

To make sure your phentermine prescription is as effective as possible, it is also a good idea to cut down on foods and drinks which cause additional acidity in your urinary pH.

Experiments have shown that, when compared to an alkaline pH, an acidic urinary pH causes phentermine to be excreted twice as fast and, therefore, less effective. Unhealthy acidifying foods and drinks to avoid include alcohol, coffee, soda, butter, and ice cream.

The main issue to stress here is that you should always follow your doctor’s instructions.

Phentermine is a prescribed medication and should be treated accordingly. You must be completely honest with your doctor in your consultations so that he or she is well-informed about your medical history and can treat you effectively.

If you have any concerns or questions about phentermine, it is always a good idea to ask your doctor – both for you to be better informed and so that your doctor can improve their care for you and future patients.

We hope that you now feel confident about phentermine and how to take it, but if you have any feedback about this article, please get in touch with us by commenting below!

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  1. I recently, one week ago, started phentermine capsule 15mg. My doctor and pharmacist said to take it after breakfast. I’m not sure why, especially as everywhere online says it’s best absorbed on an empty stomach before breakfast. Can I try taking it before eating? Why would they say after breakfast? I don’t feel like my appetite is very suppressed taking it after eating and I’d like to get the full effect of this pill.

    1. Hi Tai,

      We suggest following your prescribing doctor’s recommendations. However, some phentermine users have found that taking phentermine first thing in the morning, half an hour before breakfast, helps them maximize the pill’s wanted effects of appetite control and extra energy. You could always ask other phentermine users for their experience by joining our official facebook group: https://www.facebook.com/groups/1069871763087734

      Best regards,

      Sarah, Phentermine.com

  2. I began taking phentermine four days ago and I’ve already lost five pounds! It does exactly what it’s supposed to do: suppresses my appetite and gives me a little boost. I’m still able to eat, but I’m not constantly hungry and craving sweets! I do notice myself clenching my jaws sometimes which I hate and am trying to stay cognizant of because that’s what druggies do and I don’t want to look like I’m on meth lol… but other than that, I’ve had no negative side effects. I still sleep well, I’m not overly angry (someone mentioned that above), I’m able to eat, and I have energy to get stuff done. I have hypothyroidism so I usually feel very tired and unmotivated. Phentermine has helped that tremendously! I set an alarm and take my thyroid pill at 4 am, go back to sleep, and then take the Phen when I wake up (either 5 or 6:30 depending on the day). I skip breakfast, drink a lot of water all day, and have lunch and dinner. I don’t crave snacks in between and I’m able to eat smaller portions. I could probably skip one of those meals, but I know my body needs the fuel and needs to make these new eating habits for when I stop the Phen. I also have vitamins and supplements that need to be taken with food. If you’re on the fence about taking it, just try it and stay in close communication with your doctor. Give it a week or two and if you don’t like it, have your doctor help you stop taking it. I just wanted to share my experience for what it’s worth. If things change, I will report back.

    1. Hi April! It sounds like you’re doing AWESOME so far 😀 You give great advice. Thanks so much for sharing, and keep up the great work!
      Rachel, phentermine.com

  3. wondering if i can take this with bupropion and losartan, and if im planning on consuming alcohol since my birthdays coming up, how many days before and after should i avoid this medication.? please advise

    1. Hi Samira!

      We have a great article on the subject; you can read it here! If you continue having problems, we suggest you consult with your prescribing doctor before self-medicating with any additional supplements or medicines.



    1. Hi Tammy, thanks for your question! We’d suggest talking to your prescribing doctor about the best schedule for taking phentermine and synthroid together. These two medications can interact in some people, so it’s important that your doctor is fully aware that you’re taking both medications and helping you figure-out how to best do so. In the meantime, you may be interested in our blog post on your thyroid and phentermine.
      Rachel, phentermine.com

  4. I started phen 37.5 and I have no appetite at all. None. Is that bad to just not eat much at all? I’m simply not hungry.

    1. Hi Mary, thanks for your comment! Yes, the appetite suppressing effects of phentermine can be very strong – especially at the start. Still, you should aim to eat a minimum of about 1200 calories each day so that your body has the fuel it needs to go about your daily activities. It can actually slow your weight loss (and make the loss harder to keep off in the long-run) if you eat too little because your body thinks it’s in starvation mode. If you’re interested in reading more on this, check out our articles about eating enough on phentermine and calorie counting.
      Rachel, phentermine.com

  5. I’ve been taking phentermine for 5 days now and I’m so sad and disappointed. I don’t feel any different. No burst of energy to help me stay focused on my workouts and no change in appetite. This is supposed to be an antidepressant and help control hunger. Wht isn’t it doing that for me? Where is my emergy? I take it in the morning on an empty stomach as prescribed. Is anyone else having this problem? Does this mean it’s not working? I though it worked because it helped you not be hungry. Of course also boosting your metabolism by giving you energy. Someone please give me hope. Thank you

    1. Hi Kim! Thanks for your comment. We’d recommend checking with your prescribing doctor if you feel like your phentermine isn’t working. It may be a relatively simple fix, but your doctor is the best person to investigate why you’re not feeling the desired effects right now.

      You may also be interested in our Facebook support group to find other phentermine users who can offer support and advice on various, phentermine-related topics. Best wishes!
      Rachel, phentermine.com

    2. I took phentermine a few years ago , lost 14 pounds , Now I started taking it again and lost 3 pounds , very disappointed on the my 3 bottle now .

    1. Hi Phyllis! The recommendation is to avoid alcohol entirely while using phentermine. The problem with combining alcohol and phentermine is that phentermine is a stimulant while alcohol is a depressant. The combination can increase the risk of cardiovascular side effects, such as increased heart rate, chest pain or changes to blood pressure. You may also be more likely to experience symptoms such as dizziness, drowsiness, depression and difficulty concentrating. Your doctor can give you more information on phentermine and alcohol, so you may want to speak to him or her about this if you’re still curious. In the meantime, check out our blog post on this topic: https://www.phentermine.com/phentermine-contraindications/phentermine-and-alcohol/
      Rachel, phentermine.com

  6. My doctor prescribed Adipex-P 37.5 tablet. My pharmacy filled my prescription with generic phentermine 37.5 with the imprint k25 manufactured by kvk-tech. On the prescription insert it says to allow the tablet to dissolve on my tongue but reading the blog it looks like the only pill made to dissolve is the supremes tablet. Could you please explain how I should be taking this pill. Thanks

  7. This is my 2nd day taking the 37.5 tablet. I take it in the morning on a empty stomach. By lunchtime I’m hungry. Does it take phentermine a while to start working?

    1. Hi Kim,
      You should still get hungry on phentermine, so it’s normal to be hungry at lunchtime. Make sure to eat regular meals to stop you from getting overly hungry though.
      Sally, phentermine.com

  8. Does decaf-coffee make it less effective?
    The article mentioned avoiding coffee and soda – wondering if caffeine is the reason. Thank you!

    1. Hello Charisma. Thank you for reaching out. It is best to avoid caffeine while on phentermine. Here, we explain just how phentermine works to give you more energy, how the expectations don’t always live up to the reality, and how you can get more energy from phentermine if you’re not experiencing the increase in your energy levels that you had hoped for: Increase your energy levels with Phentermine.

      You are welcome to join our brand new support group so you can connect with other phentermine users, share your experience and get some valuable advice. https://www.facebook.com/groups/1069871763087734/

      Have a nice day!

      Rebeca, Phentermine.com

  9. Hi i am a thyroid cancer survivor and have been on a few thyroid medications..
    We had a winter storm and my car stalled out and my thyroid medication was at my parents and with the roads so bad I was without my medicine for 4 days..
    So with that back story I instantly put on 15 lbs then I got my medicine and was to see my endocrinologist and by that time another 10 lbs in less then a month ” I call it my fake weight ” as. Most is water weight but it still sucks and hurts..
    My thyroid blood work levels surprisingly were fine..
    But I was concerned Since the 4 day miss I stopped sweating ( sounds great right) no I’m a avid sweater so it was alarming..
    So my enderconolgist just prescribed phentermine after saying though my levels are good my metabolism has shut down completely and that’s why the double whammy rapid weight gain ..
    I have to take my thyroid medicine in the am on a empty stomach when I wake up, and I was just told to take pill once a day but no other information..
    Other then on a empty stomach as well..
    So I’m not sure when it’s best for me to do so I don’t think taking all three at the same time is right..
    Or if I drink coffee and then take is better after 30 mins or later I saw where it said coffee could effect the medicine acidity, but I have insomnia so I’m confused..
    Sorry so long but I oddly just want to sweat and restart my metabolism so far I take it after I drop my son off at preschool which is 3 hours after I take my thyroid medicine but I’m on day 5 and not sweating even at the gym and in sauna, I just pee a lot so I fear I’m taking it all wrong please help..
    Thanks in advance

  10. Hello I am tring to get all info on these pills before I take them. I have my bottle already but I hear a lot of negative stuff so can someone please share if you’ve had any mood changes or sress or even sight changing someone said it changes ur vision and makea you angry

  11. I just starting taking phentermine. I’m on the 15 dosage. I take it at 07.00 and eat breakfast between 08.00-08.30. I don’t see a difference in my appetite or an energy increase. Is it to early to see a change?

    1. Hi Youlanda,
      You should be feeling a difference in energy and appetite if the phentermine is working for you. It might be that the 15mg dosage is too low for you, so perhaps you could speak to your doctor about increasing your dosage.
      Sally, phentermine.com

  12. Hello,
    I just began taking Phentermine again. I took it about 6 years ago and had TREMENDOUS success. I must tell you that I have hypothyroidism and also took 400 mg of Synthroid, along with Victoza Pen,Toprimate, Super B – Complex vitamins and of course the beloved Phentermine 37.5 Capsule. I prefer the capsule over the tablet. My Endocrinologist prescribed the meds for me. I took these medications and I began to lose wight rapidly, I joined the gym for the first time in my life. It was hard, I hurt and I was in pain for about a month but it was worth it. I lost 100 pounds in 9 months. I know this may not be typical but It worked for me. I had tried EVERYTHING under the sun except surgery so I was really skeptical about this, but it worked. I unfortunately had an injury & could no longer work out, stopped the medications and put the weight back on. Today is day 2 of taking Phentermine and I am excited to see my results this time. ** FYI I am not affiliated with any company and I am not being compensated for my remarks**. I just wanted people out there who really want to lose weight to know that Phentermine 37.5 mg really works

  13. I have being eating great and I lost over 50 lb on my own thank God without this pill if I stop taking it would I gain my weight back I hope not I have being doing so good with out it and I look great too thank God but I don’t want to take it if it make it come back

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