Phentermine 30mg

Phentermine: Usages, Dosing, Side Effects

, reviewed by
 – Updated April 20, 2023
, reviewed by
 – Updated April 20, 2023
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Table of Contents


Generic name: Phentermine  [ˈntəmɪ:n]
Brand names: Adipex-P, Lomaira, Suprenza
Drug class: S6 – Stimulants
Schedule: S4
Manufacturer: iNova Pharmaceuticals
Molecular Formula: C10H15N
Create Date: 2005-03-25
Modify Date: 2022-07-23

What is Phentermine? What is it used for?

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) [1]

TGA Pharmacology Summary

Phentermine is a TGA-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


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BMI is calculated by dividing your weight in kilograms by your height in metres squared.

Enter your measurements and click ‘calculate’ for your body mass index.

If your BMI is above or below the normal range but you consider yourself to be of normal and healthy weight for your height, chat with your doctor about any potential health concerns.

This calculator has been reviewed by NeverGiveUpTeam experts and is based on reputable sources of medical research. It is not a diagnostic tool and should not be relied on as a substitute for professional medical or other professional health advice.

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;
  • overactive thyroid;
  • glaucoma;
  • 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
  • kidney disease.

Phentermine is not approved for use by anyone younger than 16 years old.


The drug is contradicted for you if you have:

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:

  • itching;
  • dizziness headache;
  • dry mouth;
  • unpleasant taste;
  • diarrhoea;
  • constipation;
  • stomach pain; or
  • increased or decreased interest in sex.

Some of the adverse effects of phentermine may include:

  • Heart palpitations
  • Raised blood pressure
  • A feeling of restlessness
  • Headaches
  • Dry mouth
  • Diarrhoea
  • Constipation
  • Hives
  • 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 TGA at 1300 134 237.

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 [2], [3].

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?

Dosing information

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 [4], [5].

what is phentermine
phentermine australia

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.


  1. Is phentermine a good option for weight loss? By Meera Shah, M.D. Mayo Clinic. [Cited Sept. 11, 2020]. Available from: [URL Link]
  2. Phentermine HCL – Uses, Side Effects, and More. WebMD. Available from: [URL Link]
  3. Phentermine. May 24, 2022. Available from: [URL Link]
  4. Side effects and precautions. Healthline. Updated on December 7, 2021. Available from: [URL Link]
  5. Phentermine and Topiramate. MedilinePlus. January 15, 2017. Available from: [URL Link]
  6. Phentermine. Related Records. National Library Of Medicine. PubChem. Available from: [URL Link]
  7. Phentermine. When and how to use. Medical News Today. January 17, 2018. Available from: [URL Link]
  8. Active ingredient: phentermine. Healthdirect. Available from: [URL Link]
  9. Phentermine Hydrochloride. PeaceHealth. Available from: [URL Link]

Popular FAQ

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.

When prescribed, phentermine is safe. Make sure your doctor knows about all your medications and health issues. It shouldn’t be used with other diet pills. Rarely people have high blood pressure.

Phentermine should not be taken if:

  • You have cardiovascular disease
  • You are taking or recently stopped taking drugs known as monoamine oxidase inhibitors
  • You have hyperthyroidism
  • You have glaucoma
  • You have a history of drug abuse or agitation
  • You are pregnant or nursing
  • You are sensitive to or had a reaction to other stimulant drugs

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 stays 4 days in your system. Half the medicine is gone after 20 hours. Drug elimination depends on several factors. Age, diet, renal and liver health are all contributors.

Doctor-prescribed phentermine use is the best one. It is usually taken first thing in the morning, 1 to 2 hours after breakfast. Phentermine might induce sleeplessness if used at night.

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.

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1 year ago
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Why should so many people know I’m taking phentermine? I’d like to keep things more private.

1 year ago
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Thanks for the answers. I really needed to read smth like that.

1 year ago
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Prepare yourself for a significant amount of pain throughout the first several weeks. I made it through the adverse effects, but it was really hard. Anyway, I have no regrets at this point. I’ve managed to lose 25 pounds!

1 year ago
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I liked the effect and the form of the drug. Capsules are so much better than injections.

1 year ago
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Wow! So many side effects; good to know before taking the drug. Thanks

1 year ago
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This is an old-school diet pill I come back to once in a while. Appetite suppressor number one for me.

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