Phentermine: Safe & Effective Weight Loss Pill for More than 65 years!

Phentermine is a safe and effective appetite suppressant which has FDA approval since 1959. Although its a controlled substance, its safe and effective and easily found and the most commonly prescribed weight loss drug.  This is a very long time for any medication. With over 70 million prescriptions written over the past 60 years in the US alone, it has proven to be a safe and effective weight loss medication. Since 2007 about 4 million prescriptions for phentermine are written each year.  This ranks phentermine in the top 300 medications prescribed in the US. Its two dimensional structure resembles amphetamine which leads to confusion on some internet blog posts. Individuals without experience often confuse the two drugs. Phentermine is not amphetamine and remains the safest, most effective treatment for obesity. Hundreds of reports  have found that  blood pressure and heart rate are not affected by phentermine. Although, it was approved for 12 weeks, off-label use has extended its usefulness for many more weeks.  The strongest version of phentermine is Adipex while the weakest and newest version(FDA approved in 2016 isLomaira.

Early Studies on Phentermine/ Adipex

The first long term study was released in 1968.  It reported on  108 obese women treated for more than 8 months.  An average weight loss of 13% was found on phentermine  and the only side effects noted were dry mouth, insomnia, and constipation all which proved unimportant.  https://www.ncbi.nlm.nih.gov/pubmed/4969672,   https://www.ncbi.nlm.nih.gov/pubmed/4889477

The first re-evaluation after approval in 1959 was in 1973 when the FDA evaluated all drugs for not only safety but effectiveness. It passed all the tests. After the phen/fen crisis in 1997, the FDA re-evaluated phentermine. The culprit was found to be fenfluramine (the 2nd fen in phen/fen.) Since then there have been no reports of phentermine causing hypertension or valvular heart disease.

Phentermine in Combination with Topiramate is called Qsymia

The FDA re-evaluated the side effects effectiveness for long term obesity treatment when it approved a new medication Qsymia – a combination of various doses of phentermine and topiramate. The FDA reviewed the results of 4500 obese people treated with different dose combinations of the two medications for 12 to 36 months. Again it was found to be safe and effective with a 9 to 12% weight loss. To ensure safety, the FDA required a separate study of possible cardio-vascular side effects:  twelve hundred obese patients were followed to examine the occurrence of any cardiovascular complications including changes in blood pressure, heart rate and Cardiac ECHO’s. No abnormalities were found. There was no elevation in blood pressure, contrary to popular opinion. This has been the experience of nearly all physicians treating obese people, even those with concurrent hypertension.

Different Versions of Phentermine Can Cause Confusion:

Brand names for phentermine are Adipex-P® and Lomaira. Discontinued brands in the US include Fastin and Ionamin. Adipex-P is a longer-acting version taken in the morning. Lomaira is a short-acting version that one can take 30 minutes before meals. Phentermine is also available under its generic name. Here is comparison of phentermine to other FDA approved weight loss medications.

Lomaira: Newest Version of Low Dose Phentermine

Most recent FDA evaluation occurred in 2016 when the FDA approved phentermine hydrochloride  in an 8 mg, a low-dose medication for adults with obesity that can be taken up to three times daily.  This new dosage form involved a short acting medication that can be taken before meals or whenever the patient is hungry and up until 4 hours before sleep. It fills in the gap between the long acting 12 hour effect of the  37.5mg extended release phentermine

Phentermine Helps You Lose Weight Safely and Quickly

Our providers prescribe phentermine to many of our overweight and obese patients based on their medical history, metabolism, and weight loss needs. When given to the appropriate patient, there is steady, predictable weight loss of 2-3 lbs. per week. Depending upon the age, gender, and starting weight of the patient, weekly weight loss can be even higher. Furthermore, this happens without any significant side effects. In fact, the only side effects we see are dry mouth and a little bit of insomnia. We eliminate the latter by taking the medication earlier in the day and avoiding caffeine after lunch.

Phentermine and the other appetite suppressants remain very effective. As a result, they play a major role in helping overweight individuals lose weight when taken in low doses and titrated slowly over time. Tens of millions of people have taken these appetite suppressors for weight loss.

Phentermine Acts on the Brain Effecting the Appetite Center

Phentermine is a sympathomimetic amine, also known as an “anorectic” or “anorexigenic” drug. According to the National Library of Medicine, phentermine’s primary mode of action is that it increases the body’s release of catecholamines. Specifically, it causes the release of epinephrine and norepinephrine, and possibly dopamine as well.

These catecholamines cause a decrease in appetite and an increase in energy expenditure by their influence on a variety of neurotransmitters and neuropeptides throughout the hypothalamus. When you are taking phentermine, you tend to feel less hungry but more energetic and alert. Increased energy expenditure will burn more calories. Weight loss results from a combination of these influences.

Phentermine Consistently Produces the Most Weight Loss

There have been over 100 clinical studies on phentermine reported in the various medical journals showing safety and effectiveness.  Here are highlights of the most significant recent studies and comparisons. Phentermine weight loss after a year was about 8.5% after a year.

More Recent Studies on Phentermine Safety and Effectiveness

UK Weight Loss Study Recently Confirms Safety and Effectiveness on Moderate Dose Phentermine and Intermittent Phentermine Dosing:

A British study found phentermine to be effective when compared to placebo over a period of months. This study included three groups of 36 women each. Two groups took phentermine to augment their weight loss efforts. In one group, doctors gave participants 15 mg per day for the duration of the study. In another group, doctors gave participants the same dose every other month. Both groups consumed a 1,000-calorie daily diet. The continuous group lost a total of 27 lbs. over the period, and the intermittent group lost slightly more at 28.7 lbs. The placebo group lost 8 lbs in the same period.  Few if any side effects were noted. Furthermore, there were NO significant differences in systolic and diastolic blood pressure between the groups. Note that the average weight was 190 lb, so the average weight loss was about 45-50 lbs over the year!

 South Korean Study of Higher Dose Phentermine:

In 2005, Korean scientists conducted a trial of this medication’s weight loss effects on 34 participants. In this study, they used the standard 37.5mg dose. Subjects were placed on a 1,500 calorie per day diet. After 14 weeks of study, the drug treatment group lost 16.5 lbs. Side effects reported in this study, similar to many other studies, were much less significant than most people think. Here is the report on side effects from the study:

“… in adverse events analysis, only 6 of 29 (20.7%) treatment group subjects had complaints about palpitations. This number is not significantly more than the placebo group. Similarly, blood pressure had not increased after the treatment period in phentermine group, and there were no significant differences between both groups. The analysis of blood pressure at the 6th week found the mean systolic pressure to be 127.4 (SD 10.2) mmHg and the mean diastolic pressure was 85.1 (SD 8.4) mmHg in the treatment group (n = 28), compared to systolic 127.3 (SD 12.7) mmHg and diastolic 83.5 (SD 10.4) mmHg in placebo group (n = 24). Therefore, we can suggest that the administration of phentermine would not induce any serious cardiovascular effect at least for the patients whose risk of cardiovascular disease is not high.”

Again we have seen a safe drug with no significant blood pressure or cardiovascular events.

More Recent Studies of Long Term Treatment with Phentermine for Obesity

In 2018 the Pennington Biomedical Center reviewed multi center studies and found a 6 to 9 % weight loss vs. 1.2% for placebo with all 9 approved weight loss medications at the end of a year including phentermine without significant side effects especially hypertension and cardiovascular disease.

In the International Journal of Obesity,  in 2002, Dr. Haddock reviewed more than 108 studies across the world covering 40 years of obesity treatment. This also included all FDA approved drugs including all doses of phentermine. He noted safety and effectiveness for all of the medications with little difference among them.

The most significant and largest review of the effectiveness and safety of phentermine was reported by Dr. Kristina Lewis et al who reported on more than 13,000 patient taking phentermine for up to 3 years in the Journal Obesity in 2019:. “The longer the treatment the more the weight loss reported”, Dr. Lewis. The study supports the effectiveness and safety of longer‐term phentermine use for low‐risk individuals. Dr Lewis reported, “In general, then patients stopped taking the medicine, weight regain was common.”

Phentermine typically has very little effect on blood pressure or heart rate. In low doses, most people experience virtually no effect on blood pressure, heart rate and even sleep.

What are the Side Effects of Phentermine?

The most common side effects reported in clinical trials were dry mouth, dizziness, insomnia, restlessness, irritability, nausea, vomiting, diarrhea, and constipation. Many of these side effects go away as we adjust to a dose that works for you and your body adjusts to the medication.

Is this Fen-Phen?

No. The old combination of phentermine and fenfluramine or dexfenfluramine caused heart valve disease due to the fenfluramine or dexfenfluramine component. In 1997, manufacturers withdrew it from the market at the request of the FDA. There is NO fenfluramine in any phentermine preparation since 1997!

Who Can Take Phentermine?

This medication is the most effective as part of a treatment plan that includes exercise, behavioral changes, and a low-calorie diet. We recommend it for people with a body mass index ≥ 30 kg/m2 or a body mass index ≥ 27 kg/m2 with medical issues such as diabetes and high cholesterol.

People with the following medical conditions should NOT take phentermine:

• A history of cardiovascular disease (hardening of the arteries, stroke, congestive heart failure, and/or moderate to severe high blood pressure)
• Overactive thyroid
• Glaucoma
• Renal impairment
• Hypersensitivity to stimulants
• People with a history of drug abuse or mental illness
• Women who are pregnant or nursing
• Anyone who is currently taking or has used a monoamine oxidase inhibitor drug (MAO inhibitor) within the past 14 days

Each individual needs to discuss the use of these medications with their personal physician to see which medications will be safe and effective.