Is Phentermine Safe for Long-Term Use? What the Research Shows

Key Takeaways:

• Phentermine is an FDA-approved appetite suppressant that has been prescribed for weight loss since 1959. Its label covers short-term use, so taking it for longer is an off-label decision made with your provider.
• Published studies of patients treated for years found no signs of addiction, drug cravings or amphetamine-like withdrawal.
• In a study of 300 patients, those on long-term phentermine kept more weight off and did not see the blood pressure increases many people worry about.
• Phentermine isn’t right for everyone. People with heart disease, uncontrolled high blood pressure, an overactive thyroid, glaucoma or a history of substance misuse, and anyone pregnant or breastfeeding, generally should not take it.

What Is Phentermine?

Phentermine is a prescription medication that reduces appetite by acting on the brain’s hunger signals. It is one of the oldest and most widely prescribed weight-loss medications in the United States. Because it is chemically related to amphetamine, it is a Schedule IV controlled substance, and many people assume it must be habit-forming. Researchers set out to test that assumption directly.

Is Phentermine Addictive?

In a study published in the International Journal of Obesity (2014), Dr. Ed J. Hendricks and colleagues at Pennington Biomedical Research Center, Chiang Mai University and the University of Colorado evaluated 269 patients who were overweight, obese or maintaining weight loss. Some had taken phentermine for up to 21 years, at doses up to 112.5 mg a day. Using standard addiction-medicine questionnaires, the researchers found:

• No signs of phentermine abuse or psychological dependence.
• No phentermine cravings, a hallmark of addiction.
• No amphetamine-like withdrawal when treatment stopped abruptly.

What Happens When You Stop Taking It?

A separate study published in the American Journal of Therapeutics (2011) followed patients who chose to stop long-term phentermine. The only change researchers saw was the return of hunger and harder-to-control eating. Patients did not crave the drug or develop withdrawal symptoms. This was the first post-marketing study to look specifically at phentermine withdrawal.

Does Phentermine Raise Blood Pressure or Heart Rate?

This is the most common concern we hear. A study published in Obesity (2011) compared 300 patients on a low-carbohydrate diet, some with phentermine and some without. Researchers found that:

• Blood pressure came down with weight loss in both groups.
• Patients taking phentermine kept more weight off and kept their blood pressure improvements longer.
• Progression to prehypertension or hypertension was slowed or reversed in the phentermine group.

That said, phentermine can raise heart rate or blood pressure in some people, which is why both are checked before and during treatment.

Possible Side Effects

Most side effects are mild and often ease after the first few weeks. The most common are dry mouth, trouble sleeping, a faster heartbeat, constipation, restlessness and irritability. Contact your provider promptly if you have chest pain, shortness of breath, fainting, or swelling in your legs.

Who Should Not Take Phentermine?

• People with heart disease, a history of stroke, or uncontrolled high blood pressure
• People with an overactive thyroid (hyperthyroidism) or glaucoma
• Anyone who has taken an MAO inhibitor in the past 14 days
• People with a history of substance misuse or agitated states
• Anyone who is pregnant or breastfeeding

Phentermine and Newer Options

Phentermine is one tool among several. Newer medications such as GLP-1s work differently, by slowing digestion and changing hunger and fullness signals, and may suit some patients better. The right choice depends on your health history, goals and budget. Learn about GLP-1 treatment or read which peptides help with belly fat.

How Xplore Health Approaches Weight-Loss Medication

Every medical weight loss plan at our Roseville clinic starts with a full evaluation, including your medical history, blood pressure and lab work. If a medication is appropriate, we monitor you closely, adjust as needed and pair it with nutrition and lifestyle coaching for results that last.

Ready to Talk About Your Options?

Request a confidential consultation with Xplore Health in Roseville, CA, or call (916) 655-0392.

References

• Hendricks EJ, Srisurapanont M, Schmidt SL, et al. Addiction potential of phentermine prescribed during long-term treatment of obesity. International Journal of Obesity. 2014;38(2):292–298.
• Hendricks EJ, Greenway FL. A study of abrupt phentermine cessation in patients in a weight management program. American Journal of Therapeutics. 2011;18(4):292–299.
• Hendricks EJ, Greenway FL, Westman EC, Gupta AK. Blood pressure and heart rate effects, weight loss and maintenance during long-term phentermine pharmacotherapy for obesity. Obesity (Silver Spring). 2011;19(12):2351–2360.

This article is for general information and is not medical advice. Talk with a licensed healthcare provider before starting or stopping any medication.