What side effects are possible with this medication?
A side effect is an unwanted response to a medication when it is taken in normal doses. A side effect may be mild or severe, temporary or permanent, but does not occur in everyone. Not everyone will experience side effects, and which side effects a person experiences cannot be anticipated.
The following side effects have been reported by at least 1% of people taking this medication. If you develop any of these side effects (or any other side effects not listed here) or they change in intensity, speak to your doctor or pharmacist for advice on managing them and on the risks and benefits of the medication.
- blurred vision
- constipation
- diarrhea
- dizziness or lightheadedness
- dryness of mouth
- fast or irregular heartbeat
- headache
- impotence
- increased blood pressure
- increased sweating
- irritability
- nausea or vomiting
- restlessness
- skin rash or hives
- stomach cramps or pain
- talking, feeling, and acting with excitement and activity you cannot control
- tremor
- unpleasant taste
Click here to learn about serious side effects that can potentially occur with any medication. These examples are provided for information purposes only and are not meant to be exhaustive. Always consult your doctor for sound medical advice specific to your particular medication and treatment.
If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online or by phone at 1-800-332-1088.
Are there any other precautions or warnings for this medication?
Be sure to inform your doctor of all your medical conditions before you begin taking a medication. Some conditions can affect how you should take this medication.
Drug dependence:
Long-term use of this medication can become habit-forming. If, after a period
of use, this medication is not working as well, do not increase the dose of
this medication without consulting your doctor.
Occupational hazards:
People taking this medication should be aware that phentermine may impair their
ability to perform potentially hazardous activities such as operating machinery
or driving a car.
Risk of primary
pulmonary hypertension (PPH): Medications in the anorectic class that
decrease the appetite increase the risk of developing PPH, an infrequent but
often fatal condition. Although phentermine has not been associated with this
condition, other anorectic medications taken for longer than three months have
been associated with a 23-fold increase in the risk for developing PPH.
The onset or worsening of shortness of breath with daily
activity, unusual chest pain (angina), fainting spells, or swelling in the
lower extremities suggests the possibility of undiagnosed PPH. If you notice
any of these symptoms, call your doctor immediately and stop taking this
medication.
Valvular heart
disease (VHD): VHD has been reported in otherwise healthy people who have
taken a combination of phentermine with fenfluramine or dexfenfluramine for
weight loss. However, no cases to date have been reported from health
professionals of this medical condition occurring for people who have used
phentermine alone.
Pregnancy: Phentermine should not be used during pregnancy.
If you become pregnant while taking this medication, stop taking it immediately
and call your doctor.
Breast-feeding:
It is not known if this medication passes into breast milk. Women should stop
breast-feeding while taking this medication.
Children: The
safety and effectiveness of phentermine has not been established for children.
What other drugs could interact with this medication?
An interaction between medications does not always mean that
you must stop taking one of them. The following medications may affect the way
phentermine works, be affected by phentermine, or increase the risk of side
effects:
- alcohol
- cocaine
- MAO inhibitors (e.g., phenelzine, procarbazine, tranylcypromine)
- non-prescription cold and allergy medications
- other stimulants (e.g., amphetamines, methylphenidate)
- SSRIs (e.g., fluoxetine, sertraline, paroxetine)
- tricyclic antidepressants (e.g., desipramine, imipramine, amitriptyline)
If you are taking any of these or other medications
(including non-prescription, herbal, and supplement products), speak with your
doctor or pharmacist. Depending on your specific circumstances, your doctor may
want to change your therapy or suggest ways of managing any interactions. Since
caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the
action of many medications, you should let your prescriber know if you use
them.