Phentermine diet pills...are they safe and effective?

I have been on phentermine and can tell you it really worked for me. Although its effectivenes dwindles over time, it can definitely get your motivation and energy levels off the ground.
My doctor explained to me that the twelve week period you mention above is an old standard based on the clinical trials they did on this medicine when it first came out. The test period was only 12 weeks and there have been no further studies. She told me that in the 40+ years this has been on the market, there have been no long-term problems associated with its use. Some of her own patients have been on it for five years (but they have to come off once in a while to renew its effectiveness).
After two babies I am back on phentermine and looking forward to a more active life and a slimmer body.

Phentermine has been approved by the FDA for the purpose of a prescription weight loss. The Weight-control Information Network (WIN) has a chart listing FDA-approved medications for the purpose of weight loss: Prescription Medications for the Treatment of Obesity.

It is important to know that these medications are approved for use for individuals who meet certain criteria; they should not be used if your friend wants to "lose 10 pounds in 10 days" or has medical contraindications. This drug should be used under the close supervision of a medical doctor, as there are side effects that need to be managed, including (but not limited to):
- Increased blood pressure and heart rate
- sleeplessness
- nervousness

Phentermine prescription weight-loss drugs is approved only for those with:
- A body mass index (BMI) of 30 and above.
- A BMI of 27 and above with an obesity-related condition, such as high blood pressure, type 2 diabetes, or dyslipidemia

Phentermine has been approved for use by the FDA for short-term use (up to 12 weeks) for adults, as an appetite suppressant (they increase brain chemicals that affect mood and appetite). Long-term use can has not been adequately studied, and beyond potential health risks, studies are suggestion this weight-loss aid may not provide any additional weight loss benefits after 12 weeks. "Phentermine and sibutramine are the most commonly prescribed appetite-suppressants in the United States".

There are two appetite-suppressant medications FDA-approved for longer-term use (up to 1 year): Sibutramine and Orlistat. These medications are used for patients who have higher BMI and have not been studied beyond 2-years of use.

If your friend's physician has prescribed the use of Phentermine for longer than 12 weeks, this is known as an "off-label" prescription, which is legal, but has not been rigorously studied for potential adverse effects. Additionally, "most studies of weight-loss drugs show that a patient’s weight tends to level off after 6 months while still on medication." Although some patients and doctors may be concerned that this shows tolerance to the medications, the leveling off may mean that the medication is no longer effective. Other individuals may experience not only "leveling off" of weight loss, but possible weight gain: "based on the currently available studies, it is not clear if weight gain with continuing treatment is due to drug tolerance".

Lastly, your question regarding the fen/phen is important to note. The "fen/phen" (a combination of fenfluramine and phentermine) is no longer available due to the withdrawal of fenfluramine (the "fen" part) from the market in 1997 after some patients experienced serious heart and lung disorders in some people.

Resources:
-Phentermine at MedlinePlus
-Weight control Information Network, National Institutes of Health (NIH)

Your friend will be happy to hear that these appetite-suppressant medications, along with diet alterations (a Registered Dietitian would be a great resource), have been proven effective in weight loss.

The down-side of using weight-loss medication (including Phentermine): once the medication is stopped, withdrawal symptoms, such as depression and extreme tiredness, may occur if used for a long period. This makes sense, as the drug itself is a stimulant, and acts on the central nervous system to change mood and increases heart rate...all to help the person lose weight. This is not a "miracle pill", as diet and exercise are still needed to lose weight, as well as maintain weight loss.

I would also suggest that your friend talk with her local pharmacist, to learn more about phentermine, and ask if the pharmacist has any literature or written drug information for her to review.