How Long Does Phentermine Stay In Your Body? Understanding Anti Suppressants


Have you heard about the new drug that helps to treat obesity? Phentermine is a prescription drug. It is available in oral capsules, oral tablets, and disintegrating oral tablets. The name of the oral capsule comes from the brand that is Adipex-P. Well for many individuals it is a life-saver, and for some, it has side effects.

Since it is a drug that controls your appetite, the effects may stay longer than it needs to. It can be detected in any aspect of your body. In this blog, we are going to understand the mechanism of Phentermine, how long it stays in your body, and its side effects. So, if you have been prescribed Phentermine, or know someone who is then this blog is for you.

How Does Phentermine Work?


Phentermine works by activating your sympathetic nervous system’s fight-or-flight response. For this reason, it is called a “sympathomimetic” or “stimulant” drug. Stimulants help the body function. Phentermine seems to reduce your appetite. Thus, it helps you consume fewer calories. This can lead to an energy deficit, meaning you burn more calories than you consume.

People also report an increase in energy when taking phentermine, which helps them work harder. How much you lose while taking phentermine depends on two factors: how much you weigh and how well you adjust your diet and exercise while taking the drug. A decrease in weight of 3 to 5 percent is considered clinically significant. This means it can have a positive impact on your overall health and well-being.

Phentermine is also a component of the prescription drug Qsymia (phentermine/topiramate). One large study found that 75% of people who used Qsymia for more than a year lost at least 5% of their weight, while those who took a placebo lost only 23%.

How Long Does Phentermine Stay In Your System?

Phentermine causes the brain to release large amounts of certain active substances. This can be seen in the secretion of happy hormones. It contains dopamine, endorphins, serotonin, and oxytocin. These may help reduce appetite and aid weight loss. A 30 mg dose of phentermine can reduce your appetite for 12 to 14 hours. It takes about 4 days for your body to get rid of phentermine after your last dose.

This can be combined with exercise and a healthy diet to start rapid weight loss. Because the body reacts by secreting hormones through the blood, it can cause side effects when you do not take your medication. If you get too much of this drug into your body, it may cause addiction. 

This will lead to rapid weight gain when the drug is removed from the diet. This means it can take 24 to 72 hours for the drug to be analyzed and up to five days for the drug to leave your body. 

Side Effects Of Phentermine

Phentermine can cause some side effects, but most of the time they become uncomfortable and unpleasant. These may include:

  • Chest pain
  • Heart racing and palpitations in the chest
  • Rumbling in the ears
  • Trouble in sleeping
  • Mood swings changes
  • Blueing of the lips and skin
  • Swelling in the legs and ankles
  • Weakness and fatigue, especially when you increase your activities
  • Shortness of breath during exercise or sleep
  • Angina means chest pain or tightness around your chest
  • Dizziness or fainting
  • Arrhythmia or negative heartbeat
  • Hypertension (blood pressure)
  • Dry mouth
  • Bad taste in your mouth
  • Vomiting
  • Constipation
  • Diarrhea

Risk Factors While Taking Phentermine

Phentermine is not recommended for use by people under 17 years of age. This medication is not recommended if you have certain health problems, including:

  • Heart disease
  • Uncontrollable blood pressure
  • Hyperthyroidism (too much thyroid hormone)
  • Glaucoma (high intraocular pressure)
  • Anxiety or stress
  • History of drug use
  • Pregnancy
  • Breastfeeding
  • Allergy to other similar stimulant drugs 

Phentermine may not be suitable if you regularly use alcohol. This combination may increase your risk of alcoholism and affect your weight loss goals. It is also not recommended if you are taking monoamine oxidase inhibitors (MAOIs). This combination can cause dangerously high blood pressure.

How Should You Take Phentermine?

You should always stick to the recommended dose given by your doctor while taking medications. Since phentermine is an anti-suppressant it is best to take it in the morning after an hour or two after having your breakfast. And since it can interfere with your sleep cycle, it should definitely not be taken in the evening.

Depending on your condition, your doctor may prescribe you this drug in small doses or large doses. For both doses, the medication can be taken three times before the meals of your day. Keep a progress check with yourself when you are starting the medication as it can help to determine the effectiveness of the medicine.

Tips To Treat Obesity

If medications do not work on you, then you can try these tips to reduce your body weight and cure obesity:

  • Do not stress about your weight. Maintaining a healthy weight can also result in craving calories which can increase your body mass.
  • Go for a physical training program, which can help you workout and focus on the areas that you need to shed weight
  • Try eating low glycemic index foods that will keep the sugar levels in check
  • Eat more servings of fiber that includes fresh fruits and vegetables
  • Avoid processed and artificial sugar in foods and beverages


Phentermine is an effective oral medication. In studies, at least 80% of participants lost at least 5% of their body weight while taking phentermine. It works by reducing appetite. You may feel more energetic while taking it. However, phentermine works best when combined with regular exercise and a low-fat diet. Phentermine is considered safe, but it does have side effects to be aware of.

Phentermine is approved for short-term use only which is 12 weeks or less. But since new research shows it may be safe, your doctor will let you use it longer. If you have heart disease, a history of drug abuse, or use alcohol regularly, phentermine may not be the best weight loss drug for you.

Dr. Jun Ren is a dedicated and experienced registered dietitian and nutritionist who is committed to helping people achieve their health goals through personalized nutrition plans. With a passion for promoting healthy eating habits and preventing chronic diseases, Dr. Ren has been able to assist numerous clients in improving their overall quality of life.

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