Specifically, the Food and Drug Administration (FDA) has approved phentermine oral tablet to help with weight loss. Doctors prescribe it for certain adults who have overweight or obesity.
This article describes possible side effects of phentermine oral tablet. It also provides information on cost savings and coupon options for phentermine. You can explore this overview article to learn more about phentermine oral tablet, including the drug’s uses, dosage, ways to save on cost, and more.
Phentermine oral tablet is a generic version of the brand-name drugs Adipex-P and Lomaira. Phentermine also comes in other forms that you swallow, but this article does not describe these forms. To learn more about these forms, talk with your doctor.
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More common side effects of phentermine
Phentermine oral tablet may cause mild or serious side effects. However, it’s unclear in phentermine studies which side effects were more common.
The sections below list the mild and serious side effects of phentermine. To learn more about your risk for the mild and serious side effects listed below, talk with your doctor.
Mild side effects of phentermine
Phentermine may cause certain mild side effects. Usually, mild side effects are temporary and easily manageable. Tell your doctor or pharmacist if you have side effects that don’t go away or become bothersome.
Mild side effects of phentermine oral tablet that occurred in studies include:
- difficulty sleeping
- headache*
- dizziness
- diarrhea
- constipation
- vomiting
- restlessness
- sexual side effects, such as erectile dysfunction or low sex drive
- dry mouth
- bad taste in the mouth
- mild allergic reaction*†
Phentermine oral tablet may cause more mild side effects than those listed above. For details, see the drug’s prescribing information.
* To learn more about this side effect, see the “Side effects of phentermine in detail” section below.
† An allergic reaction is possible with phentermine oral tablet. However, it’s unclear whether this occurred in the drug’s studies.
Serious side effects of phentermine
Phentermine may cause certain serious side effects. If you have any serious side effects from phentermine oral tablet, call your doctor right away. But if you think you’re having a medical emergency or your side effects feel life threatening, take immediate action. Call 911, or a local emergency number, or go to the nearest emergency room.
After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Visit MedWatch’s website if you’d like to notify the FDA about a side effect you’ve had with phentermine oral tablet.
Serious side effects of phentermine oral tablet that occurred in studies include:
- heart-related side effects*
- pulmonary hypertension (high blood pressure in the lungs)
- mood changes*
- psychosis*
- risk of misuse, dependence, or withdrawal†
- tremors
- severe allergic reaction*‡
* To learn more about this side effect, see the “Side effects of phentermine in detail” section below.
† To learn more about this side effect, see the “Common questions about side effects of phentermine” section below.
‡ An allergic reaction is possible with phentermine oral tablet. However, it’s unclear whether this occurred in the drug’s studies.
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Get free cardSide effects of phentermine in children
Phentermine isn’t approved for children younger than 17 years. This medication hasn’t been studied in children.
If you’d like to learn more about ways to manage weight in children, talk with your child’s doctor.
Common questions about side effects of phentermine
Here are answers to some common questions about side effects of phentermine oral tablet. If you have other questions, talk with your doctor or pharmacist.
How do side effects of phentermine in females compare with those in males?
The side effects of phentermine in females* compared to males* are expected to be the same. That said, erectile dysfunction is a possible sexual side effect that occurs only in males.
If you have concerns about side effects, talk with your doctor or pharmacist. They can give you more information about your risk.
* Sex and gender exist on spectrums. In this article, we use the terms “male” and “female” to refer to a person’s sex assigned at birth.
Does phentermine cause long-term side effects?
Yes, in some cases, phentermine oral tablet may cause long-term side effects. These can occur if you take the drug for a long time, or they can last for a while after you’ve stopped taking the drug.
Phentermine is meant to be a short-term treatment. You’ll likely take it for only a few weeks. Usually, phentermine’s side effects go away during treatment or shortly after you stop your treatment.
Examples of long-term side effects include:
- heart valve damage that can lead to other heart-related problems*
- dependence (a condition in which your body needs the drug to function like usual)
- mood changes and psychosis*
Talk with your doctor to learn more about these side effects and how to best manage them. Ask your doctor for more information about how long these side effects of phentermine may last.
* To learn more about this side effect, see the “Side effects of phentermine in detail” section below.
Is misuse, dependence, or withdrawal a possible side effect of phentermine?
Yes, phentermine has a risk of misuse, dependence, or withdrawal.
Phentermine is a controlled substance. This means it has special regulations that doctors and pharmacists must follow due to its potential for misuse. With misuse, a drug is taken in a different way from how doctors prescribe it.
Dependence is a possible side effect of phentermine. With dependence, your body needs the drug in order to function like usual. Withdrawal symptoms can occur when you stop taking a drug your body is dependent on.
Withdrawal symptoms of phentermine oral tablet can include:
- mood changes and psychosis*
- irritability
- difficulty sleeping
- extreme fatigue (low energy)
The risks of dependence and withdrawal symptoms increase with misuse or long-term use at higher doses than recommended.
If you have a history of substance use disorder, talk with your doctor before you start taking phentermine. They may recommend a different treatment to help you lose weight.
* To learn more about this side effect, see the “Side effects of phentermine in detail” section below.
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Side effects of phentermine in detail
Below you’ll find details on some of the side effects of phentermine oral tablet.
Mood changes and psychosis
Some people taking phentermine oral tablet have reported mood changes and psychosis (loss of touch with reality). It’s unclear how often these side effects occurred in the drug’s studies.
While taking phentermine oral tablet, it’s possible to have mood changes, such as:
- dysphoria (a state of unease)
- euphoria (a feeling of intense happiness or well-being)
Psychosis is also a possible side effect of phentermine oral tablet. Symptoms may include:
- delusions (having beliefs that are false)
- hallucinations (seeing or hearing things that aren’t real)
- confusing or disturbing thoughts
Ways to manage
If you have a history of mental health disorders, tell your doctor before you start taking phentermine oral tablet. They may monitor your mental health more closely during treatment with phentermine. This includes watching for changes in your thoughts, moods, or behaviors. It can also help to have a few loved ones watch for these changes.
If you experience symptoms of mood changes or psychosis, or if a loved one notices these types of changes, tell your doctor right away.
Heart-related side effects
Some people taking phentermine oral tablet have reported heart-related side effects. It’s unclear how often these side effects occurred in the drug’s studies.
Heart-related side effects with phentermine oral tablet include:
Serious heart-related side effects, such as heart valve disease, are rare. With this side effect, the damaged heart valves can affect how your blood flows through your body.
With heart valve disease, symptoms may include:
- chest pain
- irregular or fast heartbeat
- weakness
- fatigue (low energy)
- swollen feet and ankles
- shortness of breath
Certain factors can increase the risk of heart-related side effects with phentermine oral tablet. These include high blood pressure or heart disease.
Ways to manage
If you have symptoms of a heart-related side effect while taking phentermine oral tablet, tell your doctor right away.
During your treatment with phentermine oral tablet, your doctor may recommend monitoring your blood pressure and heart rate.
Also, talk with your doctor about your heart health history before you start taking phentermine oral tablet.
Headache
Some people taking phentermine oral tablet have reported headache. It’s unclear how often this side effect occurred in the drug’s studies.
With a headache, you experience a throbbing, sharp, dull, or constant pain. Usually, headaches are mild and easily managed. But if your headaches are intense or don’t go away, talk with your doctor.
Ways to manage
If you have headaches while taking phentermine, tell your doctor. They may recommend keeping a headache journal or taking certain medications to ease your symptoms.
Some ways to prevent headaches include:
- eating regular meals according to a schedule
- getting a good night’s sleep
- drinking plenty of water
- reducing physical and emotional stress with relaxation techniques, such as progressive muscle relaxation
Allergic reaction
For some people, phentermine oral tablet can cause an allergic reaction. However, it’s unclear whether this occurred in the drug’s studies.
Symptoms can be mild or serious, and they may include:
- itchiness
- skin rash
- swelling under the skin, usually affecting eyelids, lips, hands, or feet
- swelling of the mouth, tongue, or throat, which can make it hard to breathe
- flushing (temporary warmth, redness, or deepening of skin color)
Ways to manage
For mild allergic reaction symptoms, such as a mild rash, call your doctor right away. They may recommend treatments to help manage your symptoms. They’ll also let you know whether you should keep taking the medication.
For severe allergic reaction symptoms, such as swelling or difficulty breathing, call 911 or your local emergency number right away. These symptoms require immediate medical care because they can become life threatening. If you’ve had a serious allergic reaction to phentermine oral tablet, your doctor may recommend taking a different medication instead.
Warnings for phentermine
Below are some factors you may want to discuss with your doctor before taking phentermine oral tablet.
Warnings
It may not be safe for you to take phentermine oral tablet if you have specific health conditions. These are sometimes called drug-condition interactions. Other things may also affect whether phentermine oral tablet is a safe treatment option for you.
Before taking phentermine oral tablet, tell your doctor about your health and any medications you take. Things to consider include:
- kidney problems
- hyperthyroidism
- type 1 or type 2 diabetes
- heart problems
- high blood pressure
- glaucoma
- substance use disorder
- taking certain medications, such as monoamine oxidase inhibitors (MAOIs)
- past allergic reaction to phentermine
Phentermine and pregnancy
You should not take phentermine oral tablet during pregnancy. If you’re pregnant, planning a pregnancy, or can become pregnant, talk with your doctor before taking this medication. Your doctor may suggest birth control options to use during treatment with phentermine.
Phentermine and breastfeeding
It is unknown whether you should use phentermine oral tablet while breastfeeding. If you’re currently breastfeeding or planning to do so, talk with your doctor before using this medication.
Phentermine and alcohol
Phentermine oral tablet is known to interact with alcohol. Drinking alcohol while taking phentermine can increase your risk for certain side effects. Some of these side effects can include:
- headache
- dizziness
- nervousness
- difficulty sleeping
- sexual problems
- dry mouth
If you drink alcohol, talk with your doctor about whether it’s safe to consume it during your treatment with phentermine oral tablet.
What to ask your doctor
This article describes common and serious side effects of phentermine oral tablet. If your doctor prescribes this medication, they can discuss possible side effects with you. Let your doctor know if you have concerns or questions about treatment with this medication.
Here’s a list of some possible questions you may want to ask your doctor:
- Will my risk of side effects increase at higher doses of phentermine oral tablet?
- Will side effects increase as I start to lose weight while taking phentermine oral tablet?
- How do the side effects of phentermine oral tablet compare with other drug treatment options for my condition?
Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.