HomeWeight Loss BlogWhen Should I Take My Phentermine?When Should I Take My Phentermine?By Sally Cohen / 66 Comments / Phentermine / April 18, 2018 December 19, 2019In 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, as well as what to avoid while taking this medication. Before You Take PhentermineIt 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. 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 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 PhentermineIf 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. 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, or 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 may 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 exactly as prescribed by your doctor and follow all directions listed on your prescription label.Phentermine is a stimulant and can cause insomnia, so you shouldn’t take this medication later than 6pm. 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 PhenterminePhentermine can be prescribed in tablet, capsule or ODT (orally disintegrating/dissolving tablet) form. Available doses range from 8mg to 37.5mg, taken 1-3 times per day. 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 that the medication isn’t working properly and want to adjust your dose, as taking more than your recommended dosage of phentermine can cause serious, 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 PhentermineDrinking alcohol can increase the incidence or severity of certain 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 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.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 of 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, 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 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! Editor’s Note: This post was originally published January 2014, but was expanded and updated for accuracy in April 2018.