Is Phentermine FDA Approved? (For Weight Loss & Long-term Use)

January 9, 2024 |

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In this article, I will share the FDA guidelines for phentermine, its contradictions, and requirements for getting the prescription.

Phentermine was approved by FDA in 1959. This weight-loss drug works by triggering the release of neurotransmitters, leading to stress responses, including hunger suppression. It is FDA-approved only for short-term use, as prolonged consumption can cause serious cardiovascular and brain diseases.

Besides that, FDA recommends physicians not to prescribe phentermine to individuals with heart disease, overactive thyroid glands, and pregnant & breastfeeding mothers.

For the sections below, I have covered everything else you need to know about phentermine use (according to FDA), from prescription requirements to possible side effects and its classification as a controlled substance.

So, keep reading to find out whether you should be taking phentermine or not and if there’s an OTC pill equivalent to it.

What Are The FDA Guidelines For Phentermine?

FDA provides clear guidelines about phentermine usage, safety, and contradiction. That’s because this diet supplement has been widely famous for weight loss programs owing to its efficacy in hunger suppression.

Following are the recommendations provided by FDA for phen usage;

Who Can Use Phentermine According to FDA?

Due to its stimulatory properties and risk of side effects, not everyone who wants to lose weight can use phentermine. Instead, it is only approved for persons above the standard threshold of obesity.

In simple words, your BMI should be higher than 30 to use phentermine.

However, FDA allows doctors to prescribe phentermine to people above BMI 27 if they suffer from diabetes or hyperlipidemia (as these conditions can cause havoc with health when associated with excessive weight).

Phentermine can also be prescribed to hypertension patients above BMI 27, but only if their blood pressure is properly controlled within the optimum range.

Who Shouldn’t Use Phentermine According To FDA?

Phentermine is unsuitable for certain people due to specific health conditions. These include;

  • Individuals with a history of coronary artery disease, arrhythmias, stroke, congestive heart problems, or uncontrolled hypertension.
  • People who take MOI (monoamine oxidase inhibitors) drugs. Using phen within 14 days following an MOI medication should be avoided.

Besides MOI drugs, the FDA recommends not using phentermine with other diet supplements (whether prescription medicines, OTC tablets, or herbal products) and serotonin reuptake inhibitors. It’s because the safety of their co-administration with Phen is not established.

  • People suffering from hyperthyroidism, glaucoma, or kidney problems.
  • Pregnant women and breastfeeding mothers also should not use phentermine because it can cause severe health issues and abnormalities for the newborn.
  • The FDA also prohibits prescribing phentermine to individuals with a prior drug abuse record.
  • Persons who are hypersensitive to sympathomimetic amines because that’s what phentermine chemically is!

But how does an appetite suppressor medicine affect these people? The following section contains a brief catalog of its possible side effects;

Possible Side Effects Of Phentermine According to FDA

1. Increases The Risk Of Hypertension

As a psycho-stimulant, phentermine triggers stress responses in the body. Resultantly, your heart rate and blood pressure go up after taking this anorectic.

If you continue the dose for a long time, increased blood pressure can become permanent and potentially harmful, causing hypertension. This effect is especially prominent in pulmonary blood vessels.

A clinical report from Yonsei University confirms that phentermine use can cause pulmonary arterial hypertension due to its stimulatory effects.

2. Can Cause Heart And Brain Disorders

Case Studies have shown that phentermine use can lead to heart diseases like valvular disorder and ventricular fibrillation. Moreover, brain injuries like stroke, Tardive Dyskinesia, and Parkinsonism are also documented from this anorectic.

These injuries are usually associated with long-term usage, overdosing, or taking phentermine without proper medical supervision.

3. Affects Mental Health

Besides physical diseases, phentermine overdose can also negatively affect cognitive function and mental well-being.

The research catalogs contain case studies of patients who went to metal wards after taking heavy doses of phentermine. Anti-social behavior and extreme depression were the most common symptoms reported by these patients.

4. Phentermine Side Effects On Females

Usually, phentermine affects both sexes alike, but the scenario is different when it comes to pregnancy and breastfeeding.

Phen usage adversely affects pregnant women and their unborn babies. It can make the conceiving mother ill with gestational diabetes, insomnia, headaches, and nausea. These conditions make pregnancy and delivery a lot more laborious.

Besides that, its stimulatory effects can cause developmental abnormalities in unborn babies and may also make them prone to many health issues in the future.

Like pregnant ladies, phentermine is unsuitable for breastfeeding mothers because it is excreted in breast milk.

Although no side effects of phentermine use by feeding mothers are reported in newborns, health officials and FDA suspect its safety. Hence, it is better to avoid this drug for the safety of your young one.

Related: Guide on Phentermine Side Effects in Females

5. May Result In Malnutrition

Phentermine is an effective appetite suppressant. On one side, it helps to restrict calorie consumption, but on the other side, you may be tempted to eat even less than your body’s basic needs.

And if you continue using it for a long time, you will starve yourself of essential nutrients and energy.

This method is entirely counterproductive and unhealthy;

  • Your body loses strength and stamina when deprived of energy and nutrients for a long time.
  • Your metabolism slows down due to a lack of nutrition, making fat-burning more difficult.
  • Muscle mass is gradually consumed if your body is constantly deprived of proteinaceous meals.

Things To Consider Before Using Phentermine

Phentermine is not a magical solution for weight loss struggles, and neither is it a “one size fits all” drug. So, you and your physician need to consider a few things before starting this anorectic therapy;

  • Firstly, it is not a long-term solution. You can use phentermine without safety concerns for a maximum of three months. And it also does not guarantee lifelong weight management because its hunger-curbing effects disappear as soon as you stop the dosage.

Instead, you must incorporate enough physical activity and a balanced diet into your lifestyle. Otherwise, phen therapy is of little benefit.

  • As it interacts with other drugs and alcohol, you need to consider your medications and recreational intake before opting for this diet pill.
  • The risk of abuse or dependence is also a key point to remember when choosing phentermine. And if you go for phen treatment, always stick to the recommended dose.

Why Do Doctors Not Prescribe Phentermine?

Your physician may not give you a phentermine prescription even if your BMI is above 30.

Here are 8 reasons why doctors do not prescribe phentermine in compliance with FDA regulations;

Due to heart problems

Your health consultant won’t allow you to use phentermine if you suffer from a cardiovascular problem like coronary artery disease or arrhythmias.

And as discussed above, this is due to the hypertensive effects of phentermine and case studies showing the onset of heart diseases after taking phentermine.

Due to hyperthyroidism

Phentermine is also contraindicated for people suffering from hyperthyroidism (a condition in which your thyroid gland is hyperactive).

This precaution is because phentermine is known to increase thyroid activity. Thus, using the drug in hyperthyroidism can aggravate the disease and adversely affect your body’s metabolic processes.

Due to glaucoma

Hypertensive effects of phentermine can adversely affect your eyes if you are a Glaucoma patient. High blood pressure disturbs normal dilation and constriction of the pupil (the circular area through which light enters your eyes).

Due to this, your doctor will not give you phentermine because your glaucoma may worsen by taking the anorectic. This condition can cause long-term damage to your vision.

To prevent drug interactions.

If you use MOI drugs, Serotonin reuptake inhibitors, or similar drugs, your doctor will not give you phentermine to prevent dangerous drug interactions.

For the child’s and mother’s safety

As I mentioned above, phentermine usage in pregnancy can harm the mother and child. Moreover, its release in breast milk poses a risk to the health of the feeding child.

Hence, conceiving and lactating mothers would not get a phentermine prescription for losing weight.

Due to anxiety or agitation

A healthcare official is less likely to prescribe phentermine for weight loss if you are dealing with anxiety or agitation. It’s because long-term phentermine use is associated with psychosis, and when you’re predisposed to it, the results could be dangerous.

To Avoid hypersensitive reactions.

Another reason doctors do not prescribe phentermine is that it increases blood pressure and heart rate, ranking as a potential risk factor for hypertension.

Moreover, its interactions with other drugs can make your blood shoot above the limit.

So, if you have BP issues, a cardiovascular problem, or use a medication that interacts with phentermine, your doctor would justifiably advise you against this diet pill.

Otherwise, you may end up with chest pain or severe heart problems.

Due to the previous record of drug abuse

Phentermine has some potential for drug abuse and dependence. Chemically, it is a sympathomimetic amine that resembles amphetamine compounds.

As amphetamine is notorious for its drug abuse capabilities, phentermine is placed among Schedule IV drugs due to its similarity to these compounds. (These are the drugs with a low potential for abuse).

That is why your physician will not recommend using phentermine if you have a history of drug abuse.

Phentermine Alternative (Safer & Effective!)

PhenQ is manufactured by Wolfson Brands- a trusted name in the production of fitness supplements. These tablets contain a blend of L-carnitine fumarate, α-Lacys reset, Nopal, Capsimax powder, caffeine, and chromium picolinate.

All of these ingredients are obtained from natural, plant-based sources.

Hence, you can use these pills concern-free if you are vegan.

PhenQ bottle tablet

Plus, no side effects are reported from these ingredients, which makes PhenQ eligible for sale over the counter. FDA has also approved its OTC status after testing its safety level.

With these assurances of safety, let’s now move to its efficacy for weight management.

As I said before, I love PhenQ because it is a comprehensive weight loss solution, not just a drug that curbs your hunger. You get five significant benefits from these pills.

The first is obviously appetite suppression which is accredited to α-Lacys reset (a blend of ALA and cysteine). Both these ingredients reduce hunger naturally by affecting hunger hormones.

In contrast, stimulatory diet pills trigger stress hormones, causing hunger suppression as an emergency response. Such stimulatory responses are harmful, as described in the above section.

The best thing about this medicine is that it also acts as a fat burner and prevents future fat accumulation in the body. Its ingredients, L-carnitine fumarate, Capsimax powder, and Nopal cactus extracts, offer these fat-cutting characteristics.

Moreover, the addition of caffeine boosts energy, focus, and motivation level, making dieting and weight loss a lot easier and fun.

It is available from the PhenQ official website in 60-pill packing, and the pricing starts from $69.99.


When was phentermine approved by the FDA?

FDA approved phentermine usage in weight management regimens as an appetite suppressant in 1959.

Is phentermine FDA approved for long-term use?

No, FDA does not approve the long-term use of phentermine. Its recommended dosage is only up to 12 weeks.

What are the dangers of phentermine?

Phentermine use is associated with many mild and severe side effects like insomnia, headaches, nausea, high blood pressure, cerebral stroke, heart arrhythmias, and psychosis.

Is Phentermine still being prescribed?

Yes, phentermine is prescribed to overweight individuals (having a BMI of more than 30) who find it hard to restrict their calorie consumption.

What is similar to phentermine over the counter?

PhenQ is the best OTC alternative for phentermine. It is not only a safer but also a more effective weight loss drug.


The Food and Drug Administration (FDA) has approved phentermine as a prescription drug for short-term use (12 weeks) in clinical weight loss therapies. But the authority also provides clear instructions about its safety and prescription.

Firstly, phentermine is not approved for people with BMI under 30. Also, it cannot be prescribed to heart patients, individuals suffering from hyperthyroidism, glaucoma, uncontrolled hypertension, and pregnant or nursing women.

Likewise, it is unsuitable for people who use certain drugs or are hypersensitive to amines.

These individuals are recommended to consult their physicians and opt for an OTC diet pill like PhenQ for safer weight loss.

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