Phentermine and amphetamine have many similarities. It boosts your heart rate and blood pressure while decreasing your hunger by stimulating your central nervous system (nerves and brain).
People with risk factors including high blood pressure, high cholesterol, or diabetes may benefit from taking phentermine in conjunction with a healthy diet and regular exercise.
Other uses for phentermine are not included in this pharmaceutical guide.
Phentermine is most often used for weight loss but may also be used in combination with the medication topiramate to help with certain eating disorders, such as binge eating disorder (BED) 
FDA Pharmacology Summary
Phentermine is an FDA-approved weight loss drug that remains popular due to its effectiveness. A person who takes it alone or with other drugs may help boost their weight loss.
Phentermine is a Sympathomimetic Amine Anorectic. The physiologic effect of phentermine is by means of Appetite Suppression and Increased Sympathetic Activity.
Medicines that contain Phentermine
Phentermine ER (Juno), Phentermine (GH), Supremine ER, Alenami, Phentodur, Duromine, Metermine
You should avoid using phentermine when pregnant or nursing.
You should not take phentermine if you have glaucoma, overactive thyroid, severe heart problems, uncontrolled high blood pressure, advanced coronary artery disease, extreme agitation, or a history of drug abuse.
Do not use this medicine if you have used a MAO inhibitor in the past two weeks, such as isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, or tranylcypromine. There's a chance a harmful medication interaction may happen.
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Before taking this medicine
You should not use phentermine if you are allergic to it, or if you have:
a history of heart disease (coronary artery disease, heart rhythm problems, congestive heart failure, stroke);
severe or uncontrolled high blood pressure;
extreme agitation or nervousness;
a history of drug abuse; or
if you take other diet pills.
Do not take phentermine if you have taken an MAO inhibitor within the last 14 days. A harmful medication interaction is possible. Isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, tranylcypromine, and other MAO inhibitors are available.
Even if you are overweight, losing weight during pregnancy might harm your unborn child. If you are pregnant, do not take phentermine. If you get pregnant while undergoing treatment, notify your doctor immediately.
You should not breastfeed while using this medicine.
To make sure this medicine is safe for you, tell your doctor if you have:
heart disease or coronary artery disease;
a heart valve disorder;
high blood pressure;
diabetes (your diabetes medication dose may need to be adjusted); or
Phentermine is not approved for use by anyone younger than 16 years old.
The drug is contradicted for you if you have:
Known hypersensitivity or idiosyncratic reaction to sympathomimetic amines
History of cardiovascular disease (coronary artery disease, uncontrolled hypertension, arrhythmias, stroke, congestive heart failure)
History of drug abuse
Use of monoamine oxidase inhibitors (MAOIs) within the preceding 14 days
Concomitant administration of other CNS stimulants
Pregnancy and breastfeeding
Phentermine side effects
Hives, difficulty breathing, swelling of the cheeks, lips, tongue, or throat are all indicators that you may be allergic to phentermine and should call your doctor immediately.
Phentermine may cause serious side effects. Call your doctor at once if you have:
feeling short of breath, even with mild exertion;
chest pain, feeling like you might pass out;
swelling in your ankles or feet;
pounding heartbeats or fluttering in your chest;
tremors, feeling restless, trouble sleeping;
unusual changes in mood or behaviour; or
increased blood pressure – severe headache, blurred vision, pounding in your neck or ears, anxiety, nosebleed.
Common side effects of phentermine may include:
stomach pain; or
increased or decreased interest in sex.
Some of the adverse effects of phentermine may include:
Raised blood pressure
A feeling of restlessness
A higher or lower libido
This is not a complete list of side effects, and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
How does it work?
Anorectics, or “appetite suppressants,” are a family of medications that include Phentermine. By reducing your cravings and decreasing your hunger, phentermine may help you lose weight. This may eventually result in weight reduction.
While the exact way phentermine reduces appetite remains unclear, the drug is thought to act by increasing neurotransmitter levels in your brain , .
Neurotransmitters — the chemicals norepinephrine, serotonin, and dopamine — are your body’s chemical messengers.
You’ll feel less hungry as your levels of these three substances rise.
However, phentermine’s appetite-suppressing effects might wear off in a matter of weeks if you’re not careful. If this occurs, get in touch with the doctor or nurse who gave you the prescription.
How should I take Phentermine?
You should follow your doctor's instructions while using phentermine. Be sure to read and follow all instructions on the prescription label and any accompanying literature. A specialist may sometimes adjust the dosage.
In most cases, the doses are taken 1 to 2 hours before or after breakfast. Make sure you stick to your doctor's dosing recommendations.
Phentermine should never be taken in excess or for a longer period of time than prescribed. You should not change the prescribed dosage to get the most out of this medication. This medication should only be used for a limited time. Appetite suppressants may have a short half-life of a few weeks.
Phentermine has the potential to become habit-forming. Addiction, overdose, or death may all result from misuse. It is illegal to sell or give away this drug.
Contact your doctor immediately if you have not lost at least 4 pounds in the first four weeks of taking this medication.
If you abruptly stop taking this medication, you risk experiencing unpleasant side effects. Consult your physician about the safest way to quit phentermine.
Moisture and heat might damage the product, so keep it in a cool, dry place. In between uses, be sure to store the box safely and securely. Avoid taking the final dosage of the day too late if you want to avoid insomnia or difficulties sleeping or staying asleep.
Usual Adult Dose for Obesity:
8 mg orally 3 times a day 30 minutes before meals, OR
15 to 37.5 mg orally once a day before breakfast or 1 to 2 hours after breakfast.
Use: Short-term (a few weeks) adjunct in a regimen of weight reduction based on exercise, behavioural modification, and caloric restriction in the management of exogenous obesity in patients with an initial body mass index (BMI) of 30 kg/m2 or greater, or BMI of 27 kg/m2 or greater in the presence of other risk factors (e.g., controlled hypertension, diabetes, hyperlipidemia).
What happens if I miss a dose?
Make sure you don’t forget to take your medication, but if it’s already late in the day, don’t worry about missing the dosage. Take just one dosage at a time.
What happens if I overdose?
Constipation, diarrhoea, and vomiting are common side effects of an overdose. Other signs and symptoms to watch out for include shakiness, tremors, slurred speech, slowed breathing or irregular heartbeats.
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phentermine can be fatal.
What to avoid
Until you know how phentermine affects you, do not drive or engage in other potentially dangerous activities. The speed at which you’re reacting may have been slowed. Side effects may occur if you take this medication alongside alcoholic beverages.
Phentermine forms and appearance
Before 2016, the only available doses of phentermine were 15, 30, and 37.5 mg , .
PHENTERMINE 30 MG
PHENTERMINE 37.5 MG
However, the FDA authorized an 8-mg formulation (Lomaira) in 2016, which may be taken up to three times a day at least 30 minutes before meals, as a best practice.
To get the most out of your medication, you may take it once daily, either in the morning or 1–2 hours after breakfast, if the dosage is larger (15, 30, or 37.5 mg).
What other drugs will affect phentermine?
Pulmonary hypertension, an uncommon but deadly lung condition, may be induced using phentermine and other diet pills like fenfluramine (Phen-Fen) or dexfenfluramine (Redux). Do not combine phentermine with any other diet medication without consulting your doctor.
Drug interactions with phentermine are many. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any medicine you start or stop using.
What other information should I know?
Be on time for all of your doctor’s and lab visits. Phentermine and Topiramate may have various side effects, and your doctor will request testing to see how your body responds.
Do not allow anybody else to take your medicine. It’s illegal to provide or sell phentermine or topiramate to someone else. If you’re unsure about how many times you can have a prescription renewed, go to your pharmacist.
You must keep a written list of all the prescription and nonprescription (over-the-counter) medicines you are taking and any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.
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Phentermine may produce drowsiness, exhaustion, and low energy, as well as restless nights and overstimulation. Consult your physician if you experience fatigue or sluggishness while taking phentermine. You may be suffering from an undiagnosed health problem.
Phentermine is often used in conjunction with other weight-loss methods such as exercise, behavioural change, and a decrease in caloric intake. The typical course of phentermine medication is 12 weeks. Several additional factors might influence the weight-loss effects of phentermine.
Phentermine affects the brain’s neurotransmitters. It is thought to cause weight loss by suppressing appetite. The precise mechanism through which phentermine causes weight reduction is unknown. Phentermine belongs to the class of drugs known as sympathomimetic amines. Stimulant medications are the most popular term for these substances.
Phentermine is a drug approved for weight loss as part of a regimen of exercise, calorie restriction and behaviour modification. Phentermine may be prescribed for short-term treatment in people with a body mass index (BMI) of 30 kg/m2 or greater. A BMI of 27 kg/m2 or more and additional risk factors, such as high blood pressure, diabetes or high cholesterol may also warrant a prescription for this medication.
Dr. Susan Jameson is a registered chiropractor and also a qualified osteopath and homeopath. She has many years' experience in helping people regain and maintain their health. Susan uses traditional spinal and cranial adjusting techniques, massage, dry needling and therapeutic stretches and exercises to relieve pain and restore normal function. Nutritional and homeopathic medicines may be recommended to promote health and recovery.