confused woman

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, but 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 explain everything you need to know in this step-by-step guide about how and when to take your phentermine, as well as what to avoid while taking it.

Before You Take Phentermine

It is important 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 and 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, as 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.

If you have an appointment with a doctor in order to be prescribed phentermine, you should tell him or her 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 history; even if you think it is unrelated, it is important for your safety that your doctor is properly informed of any potential there may be for a negative reaction to the medication.

When to Take Phentermine

If your doctor decides that you are suitable for a phentermine prescription, he or she should provide you with clear instructions for when to take it. 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, or within two hours of eating breakfast. These instructions will vary with different phentermine brands, but you should take phentermine exactly as prescribed by your doctor and follow all directions on your prescription label.

Phentermine is a stimulant and can cause insomnia, so you shouldn’t take this medication later than 6pm, otherwise you could experience problems sleeping. However, if you have a different waking schedule, such as if you work nights or shifts, you should explain this to your doctor 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. If it is almost time for your next dose, then it is better to skip the missed dose, and you should never take extra medicine to make up for the missed dose.

woman taking phentermine

How to Take Phentermine

Phentermine can be prescribed in tablet or capsule form and an adult dosage ranges from 15mg to 37.5mg. Your dosage will be prescribed by your doctor according to your specific needs and requirements, therefore it should not be taken in larger or smaller amounts, or for longer than recommended. You should always consult your doctor if you think that the medication isn’t working properly, as taking more than your recommended dosage of phentermine can cause serious life-threatening side effects.

Phentermine side effects can include a dry mouth or an unpleasant taste in your mouth, 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 are experiencing severe side effects, then you should let your doctor know 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 certain side effects, so it is best to cut down or exclude alcohol from your diet while you are taking phentermine. Phentermine may also impair your thinking or reactions, so be careful if you drive or do anything which requires you to be alert. During the first few days of phentermine it’s advisable to monitor how you feel in order to self-assess how the medication is affecting your body. If you feel uncertain about taking on certain tasks, seek advice from your doctor if you need further reassurance.

In your first consultation you should tell your doctor about any medications or supplements you are currently taking, even if they are non-prescription, as there is the possibility of these medications and supplements interacting with the phentermine and causing it to be less effective, or worsening side effects. Your doctor may recommend that you take additional vitamins or supplements with phentermine, but 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.

In order 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. It is also important that you are 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, both in order for you to be better informed and so that your doctor can improve their service for 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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38 Responses

  1. my dr prescribed phyermine to me in what seems like a high dose twice a day he also is currently my psycheds prescriber which include anti depressants, I tried taking them last week early during the day and was still up anxious at night all night! I’m on 37.5 twice a day and am confused on when I’m to eat especially the second dose when I’m not hungry at all and food isn’t an option. I recently took a medication that put a ton of weight on me in a short amount of time after the weight gain I got discouraged and ate every little Debbie in my state and probably yours. I have a leg injury so exercise isn’t an option I see that dr in two weeks after waiting months. I have other medical issues going on and my dr is informed of all of this and everything I didn’t post

  2. Is it okay to not take phentermine on the weekend and only take it during the week?

    • Hi Lana,
      Generally phentermine is taken every day but if your doctor thinks it’s ok and it works for you to just take it during the week then there’s no reason why you shouldn’t take it this way.
      Sally, phentermine.com

  3. I have underproducing thyroid- that is being corrected by taking synthroid.

    It is ok for me to take Phentrimine safely?

    • Hey Amber,
      We have an article about taking phentermine if you have thyroid problems which you might find interesting: http://www.phentermine.com/blog/need-know-thyroid-phentermine/ Lots of people take phentermine alongside thyroid medications but it’s always best to check with your doctor before combining medications. If you have different doctors for your thyroid and to prescribe the phentermine then they should both be made aware that you are taking these two medications.
      Sally, phentermine.com

  4. Hi! I just stsrted phentermine on the 14th of August. My first and second dose gave me a lot of energy. Now I am back to no energy and feeling blah. I have lost 14 lbs thou. I see my doctor next week. Should I see about uping my dosage or taking it twice a day?

    • Hi Sharon,
      If you’re taking the maximum 37.5mg then it’s very unlikely your doctor would increase your dosage but it is worth mentioning your decrease in energy to see if he or she can alter your prescription or give you any advice on ways to increase your energy naturally or through supplements such as B12 shots.
      Sally, phentermine.com

  5. Hi, I work midnights (11-7) and wanted to start this medicine, what is the best time to take it and what is a good eating schedule?

    • Hi Michele,
      We published an article which explains how to manage your lifestyle with phentermine which you might find useful: http://www.phentermine.com/blog/manage-lifestyle-phentermine/ In your case, as you work nights it’s best to take phentermine when you wake up, rather than at any particular time of day. You should then have your first meal about an hour or so later, which could be a breakfast-type meal if you want, or could be dinner if it’s easier to eat the same as whoever you live with. Then it would be best to have your ‘lunch’ during your shift, and then a light meal towards the end of your shift, around 4 hours or more before you go to bed.
      Hope that helps!
      Sally, phentermine.com

  6. Should i take phentermine on an empty stomach? Directions just say to take the pill once a day.

    • Hi Denise,
      Normally your doctor will advise when to take your phentermine, but if you’re not sure then the usual recommendation is to take phentermine on an empty stomach first thing when you wake up, and then eat around an hour later. It’s best to check with your doctor for confirmation if you can too.
      Sally, phentermine.com

  7. I have just been giving some of this medication to take and I have not took it in years . Do you recommended taking 1/2 of it first couple days?

    • Hi Erica,
      Yes, that is usually a good idea as it is an aggressive drug so people find that taking just half to start with minimizes the side effects. If you find that you’re ok then you can increase it to a whole one after a few days.
      Sally, phentermine.com

  8. Hello I am starting phentramine and need ideas on foods exercise and the best time to take it what has worked for you let me know please

    • Hi Veronica,
      Thanks for your message! There are tons of articles on this blog with info on all these subjects – just type something you’d like to know about in the search bar and you’ll see all the related articles. If you want to chat to other users then it’s best to connect on the forum as then you can ask these questions to more experienced phentermine users. Here is the link to sign up: http://www.phentermine.com/forum/register.php
      Sally, phentermine.com

  9. Is it safe to take dayquil while taking phentermine. I have a cold/flu

    • Hi Sylvia,
      It should be fine but it’s best to ask your doctor about combining anything with phentermine – he or she will be in a better position to know your medical history and other factors which would indicate whether it is safe or not.
      Sally, phentermine.com

  10. I started taking phentermine 8 days ago. My dose is 37.5 and it is prescribed to be taken once a day. I’ve been taking it first thing in the morning and then had breakfast 15-20 minutes later. In my first week I lost 1lb (yeah, o-n-e). I read that it can also be taken 1-2 hrs after breakfast – will this change the dynamics of weight loss?

    • Hi Helen,
      It’s best to take your phentermine when you are told to take it, but this is almost always before eating and on an empty stomach. It should also be taken as early as possible in the day so as not to interfere with sleep, which is very important for weight loss. Lastly, a 1lb loss is still good, especially if you are working out like you should be, as this can increase muscle tone and make it look like you’ve lost less weight when in fact you’ve shed a few pounds of fat and built up your lean muscle – the overall loss doesn’t always show the full story. Keep at it!!
      Sally, phentermine.com

  11. Will my medical marijuana cause any life threatening side effects while using this medication?

    • Hi Chris,
      We would advise that you ask your doctor to see if there is the possibility of an interaction between phentermine and medical marijuana. Since both are prescription only then you would be able to ask when being prescribed.
      Sally, phentermine.com

  12. Hi, my ANRP has prescribed the 37.5 pill 1/2 pill twice a day. I take it 1/2 hr before I eat breakfast and lunch (my pharmacist suggestion). Will I have successfull weight loss with this dosage? Any suggestions?

  13. Hi. Can regular ibuprofen and acemptemin be taken with this? For like a headache?

    • Hi Judy,
      Yes, these are fine if you want to relieve a headache whilst taking phentermine.
      Sally, phentermine.com

  14. Ive been reading up on these pills I recently gained 30 pounds with a new bc and wanted to try these how can I get them prescribed?

  15. I am starting this tomorrow but was told by my doctor to take 1/2 hour after breakfast and 1/2 hour after lunch. I keep reading everyone is taking this before these meals. Which is right?

    • Hi Brenda,
      Usually phentermine is taken before meals but sometimes doctors advise taking it after, which may be related to your personal medical history. It is best to follow what your doctor has told you but if you can it could be useful to check why your were advised to take the phentermine after meals so you know what to watch out for when it comes to side effects and reactions.
      Hope that helps!
      Sally, phentermine.com

      • Thank you. He actually said to take 1/2 pill an hour after eating breakfast then again after lunch. After a week switch to one full pill an hour after breakfast. I will check with him and find out why 🙂 thanks again

  16. How do you actually take the pill? My doctor didn’t say anything about the method of taking it. I’ve read on some sites that you should allow it to dissolve on the tongue but your site doesn’t say anything about that. Which way is correct? Again, my doctor didn’t give me any guidance so I’ve just been swallowing it whole.

    • Hi Jen,
      The only phentermine brand which dissolves on the tongue is Suprenza, which you can read about on our site here: http://www.phentermine.com/suprenza.htm. If you have normal phentermine pills then swallowing them whole is the most effective way to take them so you are taking them correctly.
      Sally, phentermine.com

  17. Hey i have not been able to sleep at night since starting the medication 2 days ago. Any recommendations?

    • Hi Danielle,
      We have an article on insomnia which has some useful advice for you: http://www.phentermine.com/blog/insomnia-from-phentermine/ Many people who experience stronger side effects when they first start taking phentermine find it helpful to split their dosage in half if it’s in pill form. Taking a lower dosage helps users to get used to the effects of phentermine and then when they feel ready they can start to take the full dosage and should not experience such severe side effects as before. You should also make sure to take it as early as possible in the morning so that it has a chance to wear off before you go to bed.
      Sally, phentermine.com

  18. Hi I want to know what can u eat wile your taking the phentermine 37.5

  19. Should I take excedrin to help with these mild headaches. I’m afraid the caffeine wont mix right with the Phentermine 37.5 but it’s all I have on hand aside from Aleve PM which I wouldn’t want to take during the day.

    • Hi Ashley,
      A small amount of caffeine is fine in conjunction with phentermine, so it depends how much caffeine the Excedrin contains. Anything up to around 100mg of caffeine up to twice a day is fine. When you get the chance to go to a pharmacy we recommend ibuprofen as this reduces swelling and acts quickly. However, this will only treat the pain not the cause, so be sure to drink plenty of water throughout the day to avoid getting more headaches on phentermine.
      Sally, phentermine.com

  20. I feel like if I take it in the morning I will pee it out with in a hour or two then im hungry

  21. 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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