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What is Phentermine for Weight Loss?

Phentermine is a prescription medicine used for weight loss in overweight or obese people. It is used along with diet and exercise, especially in individuals with risk factors such as diabetes and high cholesterol. Phentermine belongs to a class of medications called anorectics or sympathomimetic amines. These are more commonly known as stimulant drugs and is an appetite suppressant. It works by decreasing your appetite or making you feel fuller, resulting in lower food consumption, and leading to weight loss.

Phentermine is similar to an amphetamine (a stimulant medication). It stimulates the central nervous system (brain and nerves) to increase neurotransmitter levels in your brain. Neurotransmitters - the chemicals serotonin, dopamine, and norepinephrine - are your body’s chemical messengers. When the levels of these 3 chemicals increase, your feeling of hunger decreases. Phentermine is one of several medications that are FDA-approved to help treat obesity.

Indications for Phentermine

Phentermine is usually recommended as a short-term (less than 12 weeks at a time) treatment for weight loss in individuals who are overweight or obese and who have not been able to lose enough weight with exercise and diet alone to improve their health. You are a good candidate for phentermine if you have a body mass index (BMI) of 30 kg/m2 or higher (obese) or 27 kg/m2 or higher (overweight) with other risk factors, such as diabetes or high cholesterol.

Contraindications for Phentermine

Phentermine is one of the most commonly prescribed weight-loss medications. However, it is not a good choice for individuals with:

  • Heart disease
  • High blood pressure
  • Overactive thyroid gland
  • Glaucoma
  • Hyperthyroidism
  • Those who are pregnant, may become pregnant, or are breast-feeding

How is Phentermine for Weight Loss Taken?

The typical dose of phentermine is 37.5 mg (one tablet) by mouth daily. This can be given in one dose or divided into two doses (one in the morning and one at night).  Phentermine is typically taken prior to breakfast, or an hour or two after breakfast. It should be taken precisely as prescribed by your physician. You should follow all directions on your prescription label and read all medication guides or instruction sheets. Your physician may occasionally change your dose. Follow your physician’s dosing instructions very carefully. You should never use phentermine for longer than prescribed or in larger amounts. Taking more of this medication will not make it more effective and can cause serious, life-threatening side effects. Phentermine is for short-term use only. Misuse can cause addiction, overdose, or even death. Store this medicine at room temperature away from heat and moisture. Keep the bottle firmly closed when not in use.

How Effective is Phentermine in Weight Loss Management?

The success of phentermine in helping you lose weight depends upon how well you are able to adjust your diet and how much excess weight you have while taking phentermine. There are 2 studies that directly address this question:

  • One small study from South Korea showed that almost 86 percent of individuals who were obese or overweight taking phentermine for 14 weeks lost more than 5 percent of their body weight.
  • Another South Korean study looked specifically at individuals who were obese (not overweight) and used phentermine for a 12-week course. It was noted that almost 96 percent of them lost more than 5 percent of their body weight, and 62 percent of the same group lost more than 10 percent of their body weight.

Recently, a new formulation of phentermine (Lomaira) became available in smaller 8 mg doses, which can be given up to 3 times per day. Due to potential side effects and risks, you should try to be on the lowest dose of phentermine that is effective for you for the shortest amount of time possible.

What are the Side Effects of Phentermine for Weight Loss?

As with any medicine, phentermine may cause some side effects. These include:

Common Side Effects

  • Headache
  • Dry mouth
  • Constipation
  • Tremor
  • High blood pressure
  • Diarrhea
  • Difficulty sleeping
  • Fast heart rate

Other Side Effects

  • Changes in sex drive
  • Erectile dysfunction
  • Behavioral changes
  • Dizziness
  • Restlessness

The above side effects may get better over time as your body adjusts to the medication. However, you should inform your physician immediately if these symptoms worsen over time or if you continue to experience these symptoms.

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