10 Reasons Your Doctor Won’t Give You Phentermine

by Ahmed Zayed, MD on June 12, 2024
Last updated on June 12, 2024

Phentermine pops up under cool tags like Adipex-P, Duromine, Metermine, and Suprenza. It’s not some run-of-the-mill diet pill you snag off a shelf or snag with a quick click online; it’s a potent med not designed for just anyone. Sometimes, your doc might just give a hard pass on dishing out Phentermine for you. Dive into these ten biggie reasons your doc might stash that Phentermine script out of reach.

doctor showing image on a laptop to a patient

Your BMI isn’t high enough

Body mass index (BMI) is a measure of body fat in a person’s body based on their height and weight. We calculate BMI to determine whether we’re in healthy weight range or not, and even doctors perform these calculations when assessing their patients. The ideal BMI for most adults is within 18.5 to 24.9 range. Persons whose BMI is lower than 18.5 are considered underweight while individuals with BMI of 25 to 29.9 are classified as overweight. When BMI value is 30 or greater a person is considered obese (1).

Phentermine is mainly prescribed to obese patients in order to allow them to kick-start their weight loss regimen. The drug is suitable for patients with an initial BMI ≥30kg/m2 or ≥27kg/m2 in the presence of other weight-related condition (2). Therefore, if your BMI is lower, the doctor may refuse to prescribe Phentermine.

You have glaucoma

Glaucoma is a term that refers to eye conditions which damage the optic nerve, a crucial factor for good vision. Damage to the optic nerve is caused by abnormally high pressure in the eye. Figures show that glaucoma is the second leading cause of blindness in the world and about three million Americans have it. Many people don’t even realize they have glaucoma (3).

Although it can occur at any age, glaucoma is more common among older adults. Symptoms of glaucoma vary depending on the type, but they usually include patchy blind spots in the side and central vision, tunnel vision in the advanced stages, headache, eye pain, blurred vision, eye redness, and others.

If you have glaucoma, your doctor may refuse to prescribe Phentermine. Why? You see, Phentermine is a central nervous system (CNS) stimulant meaning it exhibits sympathomimetic activity and may induce mydriasis or dilation of the pupil.

As a result, this can increase intraocular pressure and aggravate glaucoma. Patients with glaucoma should consult their doctor and see whether it would be safe for them to take Phentermine. In addition, if you changed doctor make sure your new healthcare provider knows you have glaucoma before you ask for a prescription.

You have hyperthyroidism

Thyroid, butterfly-shaped gland, is vital for the proper function of your body as it participates in many processes. The gland is prone to various problems and diseases of which hypothyroidism and hyperthyroidism are the most common. Hypothyroidism is an underactive thyroid gland marked by the lower production of hormones while the latter is overactive thyroid characterized by an excessive concentration of thyroid hormones.

Estimates show that hyperthyroidism affects 2% to 5% of all women, primarily between the ages of 20 and 40. The incidence of hyperthyroidism could be one to two cases/1000 per year, and the condition is ten times more common in women than in men (4).
Different causes can cause hyperthyroidism including the autoimmune condition Graves’ disease, family history of thyroid problems, among others. Symptoms of hyperthyroidism are numerous, and they have the potential to affect a person’s quality of life.

Hyperthyroid patients need to be careful when it comes to management of thyroid hormone levels. For example, you may need to avoid using some medications and Phentermine is one of them. Your doctor may not want to prescribe this weight loss drug to hyperthyroid patients.
If you’re wondering why it’s due to the fact that Phentermine increases the activity of thyroid gland. This can lead to higher level of thyroid hormones. Now if you bear in mind that hyperthyroidism is already indicated by the higher concentration of thyroid hormones, adding Phentermine into the mix could make it difficult for persons with this condition to regulate thyroid hormone levels and manage symptoms they experience.

You were already taking Phentermine for a while

Phentermine is one of the most widely used weight loss pills in the United States, and it’s obvious why most overweight or obese people see the drug as a sort of much-needed help for their efforts to slim down. Doctors prescribe them to patients who really need the pill to kick-start their weight loss journey, and if you’ve already used it for a while, you probably think the doctor will gladly prescribe it again, but that may not happen. How’s that possible? Bear in mind that Phentermine is a drug created to aid weight loss, but is only meant for short-term use. In fact, it is well known that phentermine can even stop working after a few months, so doctors typically prescribe for 1 to 3 months, then have patients take a break and get rechecked sometime in the future to decide whether it would be safe and productive to start phentermine again.

Healthcare providers don’t recommend the long-term use of Phentermine. Therefore, if you have been using the drug already for a certain period of time, your physician might not prescribe it in order to help you avoid complications that could arise with the long-term use of the medication. All is not lost, you have the opportunity to build on the weight loss you’ve already achieved by continuing with your diet regimen and regular physical activity.

You have a history of drug abuse

Phentermine is a stimulant, and it is a habit-forming drug. In fact, doctors only recommend their patients to take the drug for about 12 weeks or three months. That’s why your doctor may not prescribe it if you’ve already been taking the drug. When consumed for prolonged periods, Phentermine can cause habit-forming effects. More precisely, taking Phentermine for six months or longer can lead to psychological dependence and effects such as insomnia, restlessness, rapid heart rate (5) and others.

Stimulant and habit-forming effects may be particularly harmful to persons who have a history of drug abuse. For that reason, the healthcare provider might not prescribe the drug if you also had a history of drug abuse; it would bring more harm than good in the long run.

You’re using MAO inhibitors

Monoamine oxidase (MAO) inhibitors were the first class of antidepressant medications ever formulated. These drugs work by acting on neurotransmitters, i.e. they change brain chemistry to help ease symptoms of depression. An enzyme called monoamine oxidase removes neurotransmitters such as serotonin, dopamine, and norepinephrine from the brain, but the role of MAO inhibitors is to prevent that from happening (6).

If you have been using MAO inhibitors in the last 14 days, your doctor may not want to prescribe Phentermine. Basically, you shouldn’t take Phentermine within 14 days of starting or stopping taking MAO inhibitors.

Both MAO inhibitors and Phentermine are CNS stimulants. Phentermine like these antidepressants also has the potential to inhibit the activity of monoamine oxidase (7). This significantly increases the therapeutic effects of antidepressant and leads to serious complications such as damage to the heart valves, pulmonary arterial hypertension, a major increase in blood pressure (8), among others.

You have high blood pressure

High blood pressure, or hypertension, is a common problem today. The CDC reports that 75 million adults in the US or 32% of the said population has hypertension. This means that one in three adult Americans (9) have this problem which puts them in a higher risk of cardiovascular diseases. Since millions of people have hypertension, it’s highly important to manage your blood pressure and follow the doctor’s instructions.

What many people do not even realize is that Phentermine can elevate blood pressure which is bad news for persons who already have hypertension. The drug causes blood vessels to narrow and tighten. This causes obstruction in blood flow which raises blood pressure.
Higher blood pressure in a man or a woman who already has a problem such as hypertension can be incredibly dangerous and put you in a higher risk of cardiovascular events. That’s yet another reason why your doctor may opt not to prescribe Phentermine, for your own safety.

You have some heart disease

Heart disease is the leading cause of death in both men and women. Numbers show that 610,000 people die of heart disease in the US each year. In other words, one in every four deaths is attributed to heart disease. About 735,000 Americans have a heart attack each year (10).
A common reason doctor won’t give a patient Phentermine prescription is heart disease, so if you have some cardiovascular problem, you may not be able to take this drug. Phentermine is, basically, amphetamine which stimulates a part of CNS that regulates heart and blood pressure. The stimulating effects of Phentermine make cells in your heart more prone to electrical impulses.

What happens next? The drug may lead to irregular heart rhythm, but also increases the risk of heart attack and congestive heart failure. If you have some cardiovascular problem, it’s probably safer to lose weight through lifestyle adjustments, which explains why doctors avoid handing out a prescription for Phentermine in these cases.

You are irritable and agitated

Phentermine may cause restlessness and anxiety due to its stimulating effects. As a result, the drug may aggravate agitation, restlessness, anxiety, and irritability in persons who are already struggling with these problems. Since it would be difficult to manage these problems, your doctor may decide not to prescribe Phentermine.

In some instances, the healthcare provider might just lower the dosage and monitor your condition. It’s of huge importance to make sure your doctor knows if you deal with irritability and agitation to avoid potential complications later on.

You’re pregnant or breastfeeding

Some women gain more weight during pregnancy than it’s recommended and they struggle to slim down. It may be tempting to start using Phentermine to avoid excessive weight gain during pregnancy or to lose weight after giving birth to your child, but you should avoid doing so.
In fact, your doctor will definitely not prescribe the drug if you’re pregnant or breastfeeding due to potential effects it could have on the baby. Phentermine is excreted in breast milk, but at this point, it’s not quite clear how it may affect the infant.

Studies on this subject are vital so expectant, and new mothers can learn more about a safety profile of the drug before they consider using it. If you’re pregnant or breastfeeding then consult your doctor regarding healthy ways to keep weight in a healthy range or to slim down.


Phentermine is a popular weight loss drug that acts as a stimulant and appetite suppressant. Although effective, the drug may have some potential side effects of which you need to be aware before using. In some cases, doctors may refuse to give a recipe for the drug in order to protect the patient from potentially serious complications. Always consult your doctor about the pros and cons of any drug, including Phentermine.


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