All drugs should be used with caution, and only as directed by your doctor. Allergic reactions are always possible, even if you’ve taken a drug in the past. If you ever have difficulty breathing, a closing of your throat, swelling of your lips, tongue or face or hives, stop taking Phentermine right away and seek emergency medical attention.
Phentermine is habit-forming, so it should only be taken as prescribed by your doctor and for the length of time recommended--generally no more than 3 to 6 weeks. You also should not stop taking it suddenly.
Use caution when operating machinery or motor vehicles, as Phentermine can make you drowsy. Drinking alcohol can make the drowsiness worse.
If you are breastfeeding, pregnant or thinking about becoming pregnant, talk with your doctor about the risks to your baby before you start Phentermine. Also, be sure to tell your doctor about any other medicines—-prescription or over-the-counter-—that you’re taking. This includes herbal preparations and vitamins.
If you’re taking any of the following types of medicines, you must use caution if you also want to begin taking Phentermine. Be sure to talk with your doctor first.
- Certain antidepressant medicines called monoamine oxidase inhibitors (MAOIs) should not be taken within 14 days of taking Phentermine. Examples of MAOIs include phenelzine, known as Nardil; tranylcyporomine, known as Parnate; and isocarboxazid, known as Marplan.
- Tricyclic antidepressants such as Elavil, Asendin, Sinequan, Pamelor, Tofranil, Anafranil, Vivactil and Norpramin, can strengthen the effect of Phentermine.
Be sure to talk to your doctor first if you take any of these medicines.
- Phentermine may require changes in insulin or other diabetes drug therapies in order to maintain a healthy blood glucose level.
- If you take Ismelin, also known as guanethidine, for high blood pressure, talk to your doctor before starting Phentermine, because Phentermine can decrease the effectiveness of Ismelin.
There are no foods or drinks that interact with Phentermine, but you should still take Phentermine on an empty stomach to get the maximum effect.
In the past, Phentermine was marketed in combination with Fenfluramine, Pondimin and Dexfenfluramine as drugs called either Fen-Phen or Dexfen-Phen. Over time, experts found that people who took these combination drugs often developed heart valve disease. It was later proved that Fenfluramine, Pondimin and Dexfenfluramine were responsible for these side effects. Because of those findings, they were then taken off the market. Phentermine was judged to be safe and continues to be sold to this day.