Saxenda vs. Phentermine: 7 Differences Between These Weight-Loss Medications

For some people who have larger bodies, weight loss is a personal health goal. But whether it’s to manage health risks or feel more comfortable physically, losing weight can be challenging. Lifestyle changes and regular exercise are an essential part of this journey. But sometimes, weight-loss medications may be used to provide additional support.

If you’re working toward losing weight, two medication options your healthcare team may consider are Saxenda (liraglutide) and phentermine (Adipex-P, Lomaira). But how exactly do they compare? Below, we cover seven key differences between Saxenda and phentermine.

1. Saxenda is an injection, while phentermine is an oral pill

Two significant differences between Saxenda and phentermine are their dosage forms and how often you take them. Saxenda is an injection that you administer subcutaneously (under the skin). Phentermine is a pill that you take by mouth.

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Saxenda comes in a multi-dose, prefilled injection pen. Since each pen contains multiple doses, they need to be stored properly while they’re in use. Saxenda is injected once a day, at any time of day. You can pick from 1 of 3 places to inject your doses: stomach, thigh, or upper arm.

Don’t like injections? Phentermine comes in an oral tablet, capsule, or orally disintegrating tablet (ODT). These forms are usually taken once a day. The medication is also available in a lower-dose tablet (Lomaira) that’s taken 3 times a day before meals.

2. Saxenda and phentermine can both affect your appetite, but they do this in different ways

Saxenda and phentermine belong to different medication classes. They both affect appetite in a way that can help people lose weight. They just achieve this effect differently.

Saxenda is a glucagon-like peptide-1 (GLP-1) agonist. It works by acting like the natural gut hormone GLP-1. GLP-1 agonists have multiple effects on the body. For weight-loss purposes, they target areas of the brain involved in appetite and feelings of fullness. They also slow the movement of food out of the stomach, which can keep you feeling full for longer.

Phentermine is a stimulant. It’s thought to work by increasing the release of certain chemicals that activate the appetite center of the brain. This can result in reduced appetite and feelings of hunger.

3. Saxenda is meant to be taken long term, while phentermine is only approved for short-term use

Saxenda is approved for chronic weight management, meaning that it’s intended to be taken long term. Phentermine is approved for short-term use (12 weeks or less).

EXPERT PICKS: WHAT TO READ NEXT

• How they compare: Glucagon-like peptide-1 (GLP-1) agonists are a large, growing class of medications. Learn more about how GLP-1 agonists like Saxenda, Ozempic, and Wegovy compare.

• Real weight-loss stories: Three real people share their experiences taking phentermine for weight loss — from what side effects they experienced to how long it took to see results.

• A natural boost: Medications like Saxenda work by mimicking the effects of the gut hormone GLP-1. But did you know that there are foods and supplements that can increase GLP-1 levels naturally?

When phentermine was first approved, there weren’t long-term studies showing that it was safe and effective beyond 12 weeks of use. But more recently, one observational study looked at people taking phentermine for up to 2 years and found that those who took it longer saw greater weight loss without additional safety issues. So your prescriber may recommend that you take phentermine longer than 12 weeks if it’s working for you.

Phentermine is also available in a weight-loss pill called Qsymia, which is used for long-term weight management. Qsymia combines phentermine with an anti-seizure medication called topiramate.

With Saxenda, you’ll likely take it as long as it’s working for you and you can tolerate the side effects. If you stop taking the medication, it’s possible to regain most of the weight you’ve lost during treatment. So it’s generally a long-term commitment and isn’t meant to be a quick fix.

4. Saxenda may be a safer option if you have heart disease

Phentermine is contraindicated for people with heart disease. This means it could be harmful for people in this group and should be avoided. For people with heart disease, Saxenda may be a safer option.

Phentermine can potentially increase heart rate and blood pressure. There aren’t many studies looking at these risks and how they apply to people with heart disease. It’s also possible that the weight loss from phentermine could have a positive effect on blood pressure. But out of caution, it’s recommended to avoid phentermine if you have heart disease.

Across clinical studies, Saxenda wasn’t associated with an increased rate of serious cardiovascular events. And people taking it saw improvements in blood pressure, cholesterol levels, and inflammation. What’s more, the active ingredient has proven cardiovascular benefits for people with both Type 2 diabetes and heart disease. So it’s possible that people with heart disease may see additional benefits with Saxenda. 

Your prescriber can determine which option may be safest for your specific situation.

5. Saxenda is approved for a larger age group than phentermine

Along with adults who meet certain body mass index (BMI) criteria, Saxenda is approved for certain adolescents ages 12 to 17. Phentermine is only approved for people age 17 and older. 

Beyond Saxenda, there are a few other weight-loss medications approved for use in adolescents. Wegovy (semaglutide), an injection that works similarly to Saxenda, and the oral medications Qsymia and Xenical (orlistat) are all approved for people 12 and older.

6. Phentermine is a controlled substance

Unlike Saxenda, phentermine is a controlled substance, meaning that it carries a risk from dependence and misuse. This is because phentermine’s chemical structure is similar to amphetamine (the active ingredient in Adderall).

Controlled substance categories range from Schedule 1 (highest risk) to Schedule 5 (lowest risk). Phentermine is a Schedule 4 controlled substance. Amphetamine-containing medications like Adderall (mixed amphetamine salts), on the other hand, are classified as Schedule 2. So the risks associated with phentermine are typically much lower in comparison.

With Schedule 4 controlled substances like phentermine, you can refill your prescription up to five times within 6 months in most states. After that, you’ll need a new prescription.

7. Phentermine is available as a lower-cost generic, while Saxenda is brand-name only

For many people, the cost of weight-loss medications is a concern. Some insurance plans exclude these medications, including phentermine and Saxenda, from coverage. Because phentermine is available as a lower-cost generic, as well as a brand-name medication, it may be a more affordable option without coverage. Saxenda doesn’t have a generic version available yet.

When considering your options, it’s a good idea to check with your insurance plan about coverage, if you have one. That way, you’ll know how much you’ll have to pay for individual medications. You can also compare prices across weight-loss medications with GoodRx.

How much weight can you lose with Saxenda or phentermine?

Saxenda and phentermine can both help people lose weight when they’re paired with a nutritious diet and regular exercise. With these medications, people typically lose 5% to 10% of their starting body weight, sometimes more. Here’s what the research shows.

During initial clinical trials, people receiving Saxenda lost an average of about 8% of their starting body weight after 56 weeks. Over 60% of people lost at least 5% of their starting body weight. And 33% of people lost more than 10% during this period.

Across studies looking at phentermine for weight loss, most people taking the medication tend to lose at least 5% of their starting body weight after 3 to 6 months. And over half lose 10% or more.

Keep in mind that not everyone responds to weight-loss medications. It’s also possible to develop a tolerance to phentermine, causing it to stop working after a while. If you’re taking Saxenda or phentermine, your prescriber will track your progress. And they may have you stop the medication if you haven’t reached certain weight-loss goals after a period of time.

Can you switch from phentermine to Saxenda?

Yes, it’s possible to switch from phentermine to Saxenda. Phentermine is a short-term medication. So your prescriber may eventually switch you to a medication like Saxenda for long-term weight management. And if you’re unable to access Saxenda due to availability or cost, they may have you give phentermine a try.

Can you take Saxenda and phentermine together?

It may be possible to take Saxenda and phentermine together. There haven’t been extensive studies looking at the safety of combining multiple weight-loss medications. Because of this, the manufacturers of Saxenda and phentermine recommend against combining them with other weight-loss medications.

However, one small study followed people who took Saxenda and phentermine together after taking Saxenda alone for 1 year. The study found that adding phentermine didn’t result in significantly more weight loss, especially in people who had already lost a lot of weight with Saxenda. But it did seem to help with “food noise” and feelings of hunger during the first 8 weeks.

While it’s possible your prescriber could recommend taking Saxenda and phentermine together, you shouldn’t do this without their guidance.

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Written by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

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