fda approved short-term prescription weight loss drugs

The gamut of weight loss drugs are either prescription or non-prescription medications. Prescription drugs are medications that the Food and Drug Administration has approved. Also called ethical drugs, their purchase is only through the approval of a registered physician.

The different FDA-approved prescription weight loss drugs are classified into two categories. This is based on their recommended duration of use – i.e. being either a short- or long-term weight loss drug.

This article will be looking at the FDA-approved short-term prescription weight loss drugs. A future article will discuss the long-term FDA-approved weight loss drugs.

Before proceeding, prescription weight loss drugs are only for two groups of individuals. The first group is individuals who are overweight with a BMI of between 27 and 30.

The second group is individuals who are obese with a BMI of 30 or above. However, they are also to have an obesity-related condition to qualify. Some of the obesity related conditions include:

  • High blood pressure
  • Type II Diabetes
  • Hyperlipidemia – an excessive level of fats and cholesterol in the blood.

What Are They?

The currently FDA-approved short-term prescription weight loss drugs are all appetite suppressant. Appetite suppressants aid weight loss by either decreasing appetite or increasing satiety.

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Therefore they work by making you feel less hungry. They do this by increasing one or more brain chemicals that influence your mood and appetite.

Appetite suppressants stimulate the central nervous system (CNS) to affect some neurotransmitters/hormones. The neurotransmitters include the catecholamines and serotonin. The catecholamines include epinephrine (also called adrenaline), dopamine, and norepinephrine.

How Do They Work?

The stimulation of the CNS signals a fight-or-flight response from the body. This therefore makes the brain to focus more on the immediate need for energy to meet its assumed emergency need. This process makes the brain not to receive the hunger signals that might be coming from the stomach.

These approved appetite suppressants belong to a group of drugs called phenethylamines. They are like amphetamines. Amphetamines are any of a group of powerful stimulants that act on the central nervous system. They increase heart rate and blood pressure while reducing fatigue.

However, the FDA banned amphetamine use in appetite suppressants due to their dangerous side effects.

Phenethylamines are chemically like amphetamines. They however have reduced incidence of the side effects associated with amphetamines.

These appetite suppressants affect the central nervous system through several mechanisms.

The short-term FDA-approved appetite suppressants can be further divided into three major groups. Their categorization is based on their generic names or major active ingredients.


Phentermine based appetite suppressants are the most used short-term prescription weight loss drugs. The FDA approved Phentermine in 1959. It is for short-term treatment of obesity, usually no longer than six months.

Phentermine hydrochloride is the main active ingredient in Phentermine. It stimulates a group of neurotransmitters known as catecholamines. They include epinephrine (aka adrenaline), dopamine, and norepinephrine.

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Phentermine hydrochloride stimulates the central nervous system signaling a fight-or-flight response. This causes a suppression of the appetite.

Thus, Phentermine based prescription appetite suppressants helps you not to feel hungry. They make the brain not to receive the hunger signal your stomach might be sending to the brain.

Phentermine also increases the level of leptin – the hunger suppressing hormone. Leptin usually signals the brain that it is full. Phentermine also inhibits the function of another neurotransmitter known as neuropeptide Y.

Nneuropeptide Y decrease physical activity levels. It generally signals the body to eat while encouraging increased fat storage.

Thus, Phentermines have combined weight loss effects. They make a person to feel full by inhibiting hunger. They also reduce the body’s fat storage ability while increasing physical activity levels.

Side Effects of Phentermine

Phentermine might be effective in weight loss but has some side effects. The side effects have varying degrees and include the followings:

  • Constipation
  • Dry mouth
  • Insomnia
  • Blurred vision
  • Symptoms of withdrawal and addiction
  • Irritability

The safety and efficacy of combination therapy of Phentermine is not fully established. Combination of fenfluramine (Fen-phen) and dexfenfluramine (Redux) with Phentermine had adverse effects. It resulted in the development of pulmonary hypertension (a rare lung disorder) and valvular heart disease. This occurred in otherwise healthy persons.

This led to the ban on both of the above mentioned products. But Phentermine remains approved by the FDA. This is because when used alone, Phentermine does not cause any of such adverse side effects.

So, Phentermine hydrochloride is still in use today. A large number of brand names now market Phentermine. The brands include names such as Adipex-P, Fastin, Ionamin, Pro-Fast, Teramine, and Oby-trim. Others are Anoxine-AM, Phentrol, Obestin-30, and Zantryl amongst others.


Phendimetrazine is a phenylalkylamine sympathomimetic amine. It belongs to the phenethylamine class of drugs. The FDA approved it in 1976 for short-term overweight- and obesity-related health conditions.

It is an appetite suppressing weight loss medication. Like Phentermine, it functions by stimulating the central nervous system. But it has a more significant effect than Phentermine has.

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Phendimetrazine comes in two types. It has an immediate release (regular) capsule and an extended/control release tablet. Usage is two or three capsules per day or a tablet once a day.

Phendimetrazine can provide users with sustained energy levels throughout the day. However, it does not have the appetite suppressing capability of Phentermine.

For best results, Phendimetrazine is only to be used for the first few weeks of a weight loss program. Phentermine or any other potent appetite suppressant should then be added.

Nonetheless, individuals with the following health conditions cannot use Phendimetrazine:

  • High blood pressure
  • Glaucoma
  • Heart ailment
  • Arteriosclerosis

Side Effects of Phendimetrazine

Some of the side effects of using Phendimetrazine include:

  • Constipation
  • Dizziness
  • Headaches
  • Insomnia
  • Dry mouth

However, like Phentermine, Phendimetrazine is addictive. Users can become both physically and psychologically dependent on it.

Phendimetrazine is available under different brands names. Some of them include Adipost, Bontril, Plegine, Prelu-2, and X-Trozine.


Diethylpropion hydrochloride is not a very popular weight loss drug although it was approved by the FDA in 1959. It is marketed under the brand name Tenuate by Watson.

Diethylpropion is usually prescribed for short-term use as part of a weight loss plan.

It is an appetite suppressing weight loss medication. Like the other phenethylamine-like weight loss drugs, it stimulates the central nervous system. This increases heart rate and blood pressure while also suppressing appetite.

Diethylpropion is available both immediate-release tablets (Tenuate) and controlled-release tablets (Tenuate Dospan).

Diethylpropion stimulates the central nervous system resulting in appetite suppression. However, the exact mechanism by which it does this is not yet fully understood.

Side Effects of Diethylpropion

Some of the side effects associated with using Diethylpropion include:

  • Irritability
  • Headaches
  • Dizziness
  • Insomnia
  • Dry mouth
  • Constipation

Thoughts and Considerations

These prescription weight loss drugs have been in use for many years considering their time of approval by the FDA. Yet the global obesity epidemic rate has continued to drastically rise.

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First, this might be attributed to the fact they are only prescription based. Then again, they are not meant for everyone. Therefore, any intending user must be either overweight or obese to qualify for using them.

Therefore, a question arises and begging for an answer. What are individuals who are not yet in the approved categories to do with their current excess body fat?

Do they wait around till they compound their body fat and get overweight or obese? Then at that point apply for these medications to assist them in their weight loss efforts?

Given the rate at which the obesity epidemic is growing, more needs to be done and quickly. Honestly, the government and other mega pharmaceutical companies need to be more proactive.

Researchers and policy makers should step up their game to salvage the situation. Except of course, there are ulterior vested interests.