Phentermine diet plan: Tips for healthy weight loss

In this article:

• Phentermine weight loss: How the drug works in the body
• What to eat on phentermine
• Foods to avoid on phentermine
• Phentermine tips and tricks for weight loss
• Not losing weight on phentermine?

In this article

• Phentermine weight loss: How the drug works in the body
• What to eat on phentermine
• Foods to avoid on phentermine
• Phentermine tips and tricks for weight loss
• Not losing weight on phentermine?

Phentermine is a generic prescription appetite suppressant prescribed to adults with a body mass index (BMI) of 30 or higher for weight loss. It may also be prescribed to adults with a BMI of 27 or higher with a weight-related health condition such as controlled high blood pressure, diabetes, or high cholesterol. Phentermine is one of the oldest weight loss drugs on the market and is also available as brand-name Lomaira and Adipex-P. 

This drug is meant to be used in conjunction with exercise, behavior modifications, and changes in how and what you eat. As a result, people who take phentermine not only lose weight but also reduce their blood pressure and blood sugar. Here’s what to know about the best foods to eat and what to avoid on phentermine. 

Phentermine weight loss: How the drug works in the body

Phentermine belongs to a class of drugs called “anorectics” that stimulate the neurotransmitters (chemical messengers) in the central nervous system to suppress feelings of hunger and increase metabolism. 

Phentermine is a Schedule IV controlled substance, which means it has the potential for abuse and dependence. It is chemically related to the ADHD drug amphetamine and other central nervous system (CNS) drugs that are often abused. For that reason, phentermine is usually prescribed at the start of a weight-loss program at the lowest effective dose for just a few weeks. However, some healthcare providers prescribe phentermine for a longer time under close supervision. Once you take a dose, phentermine starts to work quickly and reaches the highest levels in the blood within several hours. But it can take a few weeks to see results.

“Phentermine primarily works by suppressing the appetite,” explains Jessica Cutler, MD, who performs bariatric surgery at the Maryland Bariatric Center at Mercy Medical Center in Baltimore. “Some people report increased energy and concentration on this medicine, which can help them implement better exercise and dietary choices.”

Phentermine is typically taken once daily before breakfast or one to two hours after breakfast. Some people take smaller doses more often if recommended by their healthcare provider.

What to eat on phentermine

While there is no specific list of foods that comprise a phentermine diet, and there is no particular phentermine diet plan, there are definitely some foods you will want to focus on. The best foods to eat while taking phentermine are foods that you’ll want to eat regardless of whether you’re on weight loss medication: foods that are a good source of fiber, antioxidants, and other nutrients that can help keep you feeling energized.

“Aim to eat a diet that incorporates enough protein to maintain your body’s muscle mass and enough vitamins and fiber to maintain your body’s other systems,” Dr. Cutler advises. “It is possible to lose weight in an unhealthy manner, but it is important to lose weight in a healthy way,” she says. Being mindful of your diet can help you lose weight while staying healthy.

RELATED: Best diet for weight loss

“Aim to eat foods that provide nutrients like potassium, magnesium, vitamin C, and calcium,” says Sue-Ellen Anderson-Haynes, a registered dietitian, spokesperson for the Academy of Nutrition and Dietetics, and founder of 360Girls&Women. Choose whole grains like millet, oats, buckwheat, and brown rice. Focus on nuts, seeds, yogurt, vegetables, and fruits like blackberries and blueberries. “Fruits and non-starchy vegetables are low in calories, and they naturally contain water to help keep you hydrated,” Anderson-Haynes says. This is important since phentermine may cause you to have a dry mouth.

Foods to avoid on phentermine

The foods you should avoid on phentermine are the same foods you should avoid if you want to lose weight. Some specific foods to avoid include:

• High-calorie, highly processed foods – “This includes fried and fast foods and processed items like chips and commercial baked goods,” Cutler says.
• Chocolate – It is a mild stimulant and could interact with phentermine to increase your seizure risk.
• Caffeinated beverages – Dual stimulants—such as phentermine and coffee or tea, for example—may increase the likelihood of hypertension or seizures. Ask your healthcare provider what caffeine limits are appropriate for you.

Phentermine tips and tricks for weight loss

In addition to being mindful of the foods you eat while taking phentermine, keep the following tips in mind for optimal weight loss:

• Be active every day. This means incorporating some easy ways to increase the amount of exercise you get during the day. “Take the stairs, walk your dog, and get in the habit of taking a little stroll after meals,” advises Anderson-Haynes.
• Build strength training into your routine. Lift weights if you have them, but be sure to consult a personal trainer or your healthcare provider first. If you don’t have weights, use your own body weight by doing planks, push-ups, and wall push-ups, Anderson-Haynes recommends. 
• Avoid eating late at night. An animal study on the effects of a high-fat diet in mice found that mice who ate at night, which is when they’re most active, gained less weight than the mice restricted to only eating during the day, which is when they are normally inactive.
• Be mindful of portions when you dine out. Restaurant portions tend to be oversized. Cut your entrée in half and ask the server to box up half of it to take home.
• Commit long-term. Whatever changes you decide to make on your weight-loss journey, try to stick to it. “Set smaller ‘stepping-stone goals’ rather than one single goal weight,” Cutler says. “And celebrate your ‘non-scale’ victories, like being able to do an activity you used to avoid because of joint pain or losing inches from your waistband.” These small victories can motivate you to stay on track with your healthy eating plan even when you stop taking phentermine, she says.

Not losing weight on phentermine?

Since phentermine is only FDA approved as a short-term treatment, you may want a phentermine alternative that can be used for a longer period of time. Alternatively, you may experience adverse effects from phentermine, such as heart palpitations, increased blood pressure, restlessness, trouble sleeping, or dysphoria (feeling uneasy, unhappy, or unwell). Some alternatives to phentermine include Zepbound (tirzepatide), Saxenda (liraglutide), Wegovy (semaglutide), or Contrave (naltrexone/bupropion).  

RELATED: Phentermine vs. Mounjaro │ Phentermine vs. Ozempic

Cutler recommends talking to your healthcare provider about your weight loss goals. There are other options for weight loss that include bariatric surgery, nutrition education, and habit retraining. Your healthcare provider may help you come up with a plan after considering your medical and family history, medical conditions, and medications.