Weight Loss Drugs: What are they? How do they work? What are the side effects? How does nutrition fit in?

The latest numbers show that 73 percent of adults in the U.S. are experiencing overweight or obesity and almost half are trying to lose weight (1,2). Losing weight and keeping it off are no easy tasks. Making healthy lifestyle changes, and sustaining  them for weeks, months, and years can be very difficult (3). 

Choosing more nutritious foods in optimal amounts and increasing physical activity are wise moves for just about everyone’s physical and mental health. Losing 5-10 percent of weight helps to lower triglycerides, blood pressure, and blood sugar levels (4). However, even after implementing a healthier lifestyle, there may be a need to further reduce weight (3).

The good news is that there are a number of weight loss medications approved by the FDA for long-term use. They’re also known as “anti-obesity medications” (AOMs) (5). These medications can provide some extra help. They’re meant to be used  in addition to  healthy eating habits and regular physical activity because these medications aren’t as effective on their own (3,4,5,6). 

Most of these anti-obesity medications require a prescription from your doctor.  They are mainly for people who have already tried to lose weight through nutrition and exercise efforts, and either have a BMI of at least 30, or have a BMI of at least 27 plus a health condition like diabetes or high blood pressure for which there would be a great health benefit to lose additional weight (5,7).

The purpose of these medications is to help manage weight while already eating a nutritious diet and doing regular physical activity (7). Combining one of these medications with a healthy lifestyle will help to boost weight loss by 3-12 percent more than diet and lifestyle changes alone (4,7). They are not recommended for anyone who is pregnant, breastfeeding, or trying to get pregnant (7).

This article briefly discusses some of the basics of taking these medications, such as their benefits, how they work, their side effects, as well as some important nutrition strategies you need to know when taking one of these medications.

What are the anti-obesity medications and how do they work? 

There is a wide selection of long-term anti-obesity medications to choose from (5). There isn’t one that is going to be the most effective for everybody and it’s not possible to know for sure which would work best for you or how effective it will be (5). Start with a conversation with your doctor to help decide where to start. Based on your current health status, other medications and supplements you’re taking, and your family history, along with how costly the medications are and their associated side effects, you and your doctor can decide next steps (4,5).

According to the Obesity Medicine Association, “All weight loss medications work best in the context of a healthy eating plan and exercise” (5). There are several different ways that these anti-obesity medications work. Most help you to feel less hungry, to feel fuller faster, and/or to reduce cravings (5,7). They do this by interacting with hormones (e.g., leptin, ghrelin), neurotransmitters (e.g., GABA, serotonin), and peptides (e.g., GLP-1) found in the brain, gut, and fat tissue (5,6). 

This physiological strategy works because when you feel less hungry, feel fuller faster, and have fewer cravings, it becomes easier to consume fewer calories, resulting in weight loss (6). 

Orlistat works differently because it impacts the way the digestive system absorbs fat (7).

Semaglutide, tirzepatide, and liraglutide 

Semaglutide and tirzepatide are weekly injections. Semaglutide is a glucagon-like peptide-1 (GLP-1) receptor agonist and tirzepatide is a GLP-1 and GIP dual receptor agonist (4,5). They work by targeting areas of the brain that manage appetite and food intake (4,5). The dosages start low and are gradually increased over the course of 16-20 weeks (5). The reason for starting with a lower dosage is to reduce side effects (e.g., gut issues, headaches, dizziness, and fatigue) (5). 

Liraglutide is a daily injection that acts on gut hormones to help feel fuller faster and to decrease hunger (5). 

Naltrexone-bupropion

These tablets are a combination of two different medications including an antidepressant that can help weight loss and an opioid receptor antagonist that helps with alcohol and drug dependence (4,5). Taking these together can impact the pleasure-reward area of the brain to help to feel fuller faster and decrease appetite and cravings (4,5). 

Phentermine and phentermine-topiramate 

Phentermine is the oldest and most commonly used anti-obesity medication (5). Phentermine is a pill that works by reducing appetite to make you less hungry (4). When combined with topiramate (used to help with seizures and migraines), they work together to further reduce appetite and cravings (5). 

Orlistat 

Orlistat is different from the rest of the long-term anti-obesity medications. It’s available by prescription and a reduced strength version is non-prescription (7). Orlistat capsules are taken with meals and work to reduce the body’s ability to break down and absorb fat from foods and drinks by about 30 percent (8). It does this by preventing the enzymes that digest fat from working (5). This means that, instead of absorbing the calories from fats, they continue traveling through the digestive system and are eventually excreted. 

What are some common side effects of anti-obesity medications? 

While these medications are safe when used as directed, there are some side effects to be aware of (6). Most of the side effects are mild and many improve  with continued use (4). The most common side effects affect the digestive system, such as nausea, constipation, and diarrhea (7,8). Some people may also experience dry mouth, abdominal pain, vomiting, headaches, dizziness, nervousness, insomnia, and tiredness (5,7,8). As with any medication, there is a small chance of serious side effects (7).

With orlistat, the unabsorbed fats going through the digestive tract undigested can lead to some common side effects that include abdominal pain, loose stools, and passing more gas (4,7).

Another common experience with anti-obesity medications is regaining some of the lost weight after stopping their use (4,5,7,8). This is the body’s natural metabolic response to weight loss—including weight loss with or without medications (5). This is partly due to a decrease in resting metabolic rate, as well as impacts to the hormones that make you feel hungry and full (5). According to the Mayo Clinic, “practicing healthy lifestyle habits may help limit weight gain” (7).

It’s important to stay in touch with your doctor when taking any anti-obesity medication, and to contact them if you experience any negative effects (6). You may need to follow up regularly to share how you’re feeling, what side effects you’re experiencing, and how much weight you’ve lost so far (7). These can help you and your doctor determine whether the medication is working for you, whether to switch to another one, and when to stop taking it (7).

What is the medical nutrition therapy (MNT) you need to know when taking anti-obesity medications]? 

The most important thing to consider when taking any of these anti-obesity medications is to maintain healthy eating habits. This means that you’re getting all of the essential nutrients and eating the optimal quantities of food to help you reach your weight loss goals. Avoid weight loss programs that have too many unrealistic promises (1). 

According to the National Institute of Diabetes and Digestive and Kidney Diseases, a safe and successful weight loss program includes “a healthy, reduced-calorie eating and drinking plan, a plan for increasing physical activity if appropriate, guidance and support for adopting these lifestyle habits, and a plan for keeping the weight off” (1). 

The purpose of a good weight loss program is to set realistic weight loss goals, promote healthy long-term behaviors, and provide techniques to track progress and overcome barriers (1). Ideally, all of the elements listed above would be tailored to your specific situation by a healthcare professional such as a Registered Dietitian (RD).

While there is no one-size-fits-all weight loss program, there are some important nutritional guidelines to keep in mind when working toward losing weight:

• A realistic weight loss goal is to lose about one pound per week (9)

• Focus on highly nutritious, filling, fiber-rich foods like fruits, vegetables, and whole grains (9)

• When it comes to meat and dairy, choose leaner cuts and lower fat options (9)

• Minimize less nutritious foods (e.g., fried foods, or those high in sugar or salt) (8,9)

• Keep portion sizes in check (8,9)

• Choose water as your go-to beverage (9)

• Increase the amount of physical activity you do on a regular basis (9)

Because orlistat works to prevent fat digestion, there are a few additional nutrition recommendations specific to this medication.

• Reducing the absorption of fats can also reduce the absorption of some essential vitamins and minerals. Talk to your trusted healthcare provider about including a multivitamin or other supplement (8). 

• Many of the gut side effects can be reduced by pairing orlistat with a diet that’s lower in fat (5).

Bottom line

According to the Mayo Clinic, “Weight-loss drugs aren't an easy answer to weight loss. But they may help you make the lifestyle changes that you need to practice to lose weight and improve your health” (7).

Do you need help making lifestyle changes that can lead to sustainable weight loss with or without anti-obesity medication ? As a Registered Dietitian,  I’d love to help. Take the next step and book a consult: https://www.ericabattin.com/book

References

1. National Institute of Diabetes and Digestive and Kidney Diseases. (2024, February). Choosing a safe & successful weight-loss program. U.S. Department of Health and Human Services, National Institutes of Health. Retrieved January 14, 2025, from  https://www.niddk.nih.gov/health-information/weight-management/choosing-a-safe-successful-weight-loss-program

2. National Center for Health Statistics. (2018, July 12). Attempts to lose weight among adults in the United States, 2013–2016. Centers for Disease Control and Prevention. Retrieved January 14, 2025, from https://www.cdc.gov/nchs/products/databriefs/db313.htm

3. Mayo Clinic. (2023, November 1). Weight loss basics. Retrieved January 14, 2025, from https://www.mayoclinic.org/healthy-lifestyle/weight-loss/basics/weightloss-basics/hlv-20049483

4. National Institute of Diabetes and Digestive and Kidney Diseases. (2024, June). Prescription medications to treat overweight & obesity. U.S. Department of Health and Human Services, National Institutes of Health. Retrieved January 14, 2025, from https://www.niddk.nih.gov/health-information/weight-management/prescription-medications-treat-overweight-obesity

5. Obesity Medicine Association. (2024, January 26). Top weight loss medications. Retrieved January 14, 2025, from  https://obesitymedicine.org/blog/weight-loss-medications/

6. Cleveland CliniTop Weight Loss Medications | Obesity Medicine Associationc. (2023, November 20). Appetite suppressants. Retrieved January 14, 2025, from https://my.clevelandclinic.org/health/treatments/9463-appetite-suppressants

7. Mayo Clinic. (2022, October 29). Prescription weight-loss drugs. Retrieved January 14, 2025, from https://www.mayoclinic.org/healthy-lifestyle/weight-loss/in-depth/weight-loss-drugs/art-20044832

8. Medline Plus. (2023, July 8). Weight-loss medicines. U.S. Department of Health and Human Services, National Institutes of Health. Retrieved January 14, 2025, from https://medlineplus.gov/ency/patientinstructions/000346.htm

9. Johns Hopkins Medicine. (n.d.). Medical nutrition therapy for weight loss. Retrieved January 14, 2025, from https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/medical-nutrition-therapy-for-weight-loss