GLP-1 vs. Phentermine: Which Weight Loss Medication Fits You?

GLP-1 medications and phentermine are both prescription options for medical weight loss, but they work differently, are taken differently, and are screened differently. In our program, a GLP-1 medication is a weekly injection that mimics a natural fullness hormone. Phentermine is a daily pill that suppresses appetite through the central nervous system and is meant for short-term use. Neither one is better in general. Which one fits you, if either does, is a clinical decision our nurse practitioner team makes with you at a complimentary consultation, after a health assessment and a review of your lab work.

Prefer to watch first? In a 24 second video on who qualifies for weight loss injections, Jackie Umgelder, Lead Medical Assistant at Express Med Spa, explains that the choice between the two is made at a complimentary consultation. This guide explains what goes into that decision.

GLP-1 vs. Phentermine at a Glance

Use this table as a starting point for the conversation, not as a way to choose on your own.

Both are prescribed only after a health assessment and lab work review, and both work alongside changes to eating and activity rather than replacing them. Individual results vary with either medication.

How GLP-1 Medications Work

GLP-1 stands for glucagon-like peptide-1, a hormone your body releases naturally after you eat. It signals fullness to the brain, slows how quickly the stomach empties, and helps regulate blood sugar. A GLP-1 medication mimics that hormone, and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) describes this class as targeting areas of the brain that regulate appetite and food intake. The intended effect is that smaller portions may feel more satisfying, although how strongly any one person responds varies.

At Express Med Spa, the medication is part of a nurse-practitioner-led GLP-1 medical weight loss program, not a subscription. It is a weekly injection, and injection training is included. Dosing starts low and increases gradually over several weeks. That titration is deliberate: it helps keep side effects manageable while your body adjusts, and your dose is reviewed at regular check-ins.

The medication is not meant to do the work alone. NIDDK notes that weight management medications do not replace physical activity or healthy eating habits, and our program includes nutrition guidance alongside the medication. Results vary by person.

How Phentermine Works

Phentermine is an oral prescription appetite suppressant. MedlinePlus places it in a class of medications called anorectics and explains that it works by decreasing appetite. It acts on the sensation of hunger rather than on the hormonal fullness pathway that GLP-1 medications target, which is why the two are not interchangeable and why one can suit a patient the other does not.

The phentermine prescribing information on DailyMed describes it as a short-term aid, for a few weeks, within a weight reduction plan built on exercise, behavior changes, and reduced calories. The label also notes that tolerance to its appetite-suppressing effect usually develops within a few weeks, and that when it does, the medication should be stopped rather than taken at a higher dose. It is usually taken once a day, and late-evening doses are avoided because they can interfere with sleep.

Phentermine is a Schedule IV controlled substance. Its label explains that it is chemically related to amphetamine, and MedlinePlus notes that it can be habit-forming and that prescriptions may be refilled only a limited number of times. At Express Med Spa it is the pill-form option for patients who are not candidates for injectable therapy or who do not want it, and like every medication we prescribe, it is dispensed only when clinically appropriate.

Who Qualifies for Each Medication

The BMI requirement for weight loss medication is similar for both options. What separates them is the rest of your health history.

GLP-1 medication. NIDDK explains that a health care professional may prescribe weight management medication for adults with a BMI of 30 or higher, or 27 or higher with a weight-related health problem such as high blood pressure or type 2 diabetes. Meeting a BMI threshold is the starting point, not the decision. Your nurse practitioner reviews your health history, your full medication and supplement list, and your lab work, and discusses risks, side effects, and alternatives before anything is prescribed.

Phentermine. Its label describes use for people with a starting BMI of 30 or higher, or 27 or higher with other risk factors such as controlled high blood pressure, diabetes, or high cholesterol. At Express Med Spa, the answer to who qualifies for phentermine is narrower than the BMI alone suggests. It depends on your health history, current medications, and cardiovascular picture, and our phentermine program requires well-controlled blood pressure.

NIDDK also makes the point plainly: weight management medications are not for everyone with a high BMI. That is why phentermine requirements and GLP-1 criteria are both confirmed at your consultation, not from a chart.

What Rules Out Each Medication

What disqualifies you from weight loss injections is different from what rules out phentermine.

GLP-1 medication. Supervised GLP-1 therapy is not appropriate for everyone. Our nurse practitioner team reviews your history for, among other things:

• A personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2 (MEN2)
• Current or recent pancreatitis
• Pregnancy, plans to become pregnant, or breastfeeding
• Severe gastrointestinal disorders, including gastroparesis
• Type 1 or insulin-dependent diabetes that needs close specialist oversight
• Known hypersensitivity to GLP-1 medications
• Certain kidney or liver conditions identified during lab review

GLP-1 medication carries a boxed warning tied to certain thyroid-cancer history, so your personal and family history is reviewed carefully before anything is prescribed.

Phentermine. According to its prescribing information on DailyMed, phentermine should not be used by people with:

• A history of cardiovascular disease, such as coronary artery disease, stroke, irregular heart rhythms, congestive heart failure, or uncontrolled high blood pressure
• Use of a monoamine oxidase inhibitor (MAOI), a type of antidepressant, now or within the past 14 days
• An overactive thyroid (hyperthyroidism)
• Glaucoma
• Agitated states
• A history of drug misuse
• Pregnancy or breastfeeding
• A known hypersensitivity to sympathomimetic amines, the drug family phentermine belongs to

The label also advises caution with even mild high blood pressure, and our phentermine program requires well-controlled blood pressure.

If something on either list applies to you, it does not mean there is nothing available. It means the conversation starts somewhere else, and your consultation is where that alternative gets built.

Side Effects Compared, and When to Call Us

The side effects patients most often report early in a GLP-1 program are nausea, constipation, diarrhea, fatigue, and appetite changes. They tend to appear as the dose increases, which is the main reason titration is gradual. Your nurse practitioner monitors your response at each check-in and adjusts, including holding a dose rather than increasing it when that is the more cautious choice. Rare but serious risks include pancreatitis and gallbladder problems.

For phentermine, MedlinePlus lists dry mouth, an unpleasant taste, diarrhea, constipation, and vomiting among its possible side effects, and the label lists a faster heartbeat, raised blood pressure, restlessness, dizziness, and trouble sleeping among its reported reactions. The label also notes rare reported cases of a serious lung condition, primary pulmonary hypertension, and of heart valve disease in people taking phentermine.

Call the clinic between visits, rather than waiting for your next appointment, if you notice any of these:

• On a GLP-1 medication: nausea or vomiting persistent enough to affect hydration, constipation that does not resolve, being unable to keep food or fluids down, or severe or persistent abdominal pain.
• On phentermine: heart palpitations, raised blood pressure, restlessness, dizziness, tremor, trouble sleeping, chest pain, shortness of breath, swelling of the legs and ankles, or difficulty doing exercise you have been able to do. Call right away for any of these.

If symptoms feel like a medical emergency, seek emergency care first and tell us afterward.

How Long Each Medication Is Taken

GLP-1 therapy is an ongoing program. Dosing steps up gradually over the first weeks, check-ins continue on a regular schedule, and you do not necessarily stay on medication indefinitely. How you come off it is planned: our nurse practitioner team provides guidance on maintaining your weight with lifestyle adjustments and, when appropriate, on transitioning off medication gradually rather than stopping abruptly.

Phentermine is meant for a shorter window. Its label describes it as a short-term aid, for a few weeks, and MedlinePlus notes that the length of treatment depends on how you respond to the medication.

Either way, go in with realistic expectations about stopping. Appetite typically returns when GLP-1 medication stops, and NIDDK notes that people probably will regain some weight after stopping a weight management medication, while healthy eating and activity habits may help limit that. Individual outcomes vary.

What Happens at the Consultation

Every patient starts with a complimentary consultation. It is required before you enroll, it is where candidacy is decided, and it follows the same sequence at every Express Med Spa location:

• Health and weight history. What you have tried, what worked, what did not, and what changed.
• Medication and supplement review. Bring a list of everything you take, including over-the-counter products.
• Lab work. Labs must be current within 90 days. Our team tells you which panel is needed, or orders it.
• Eligibility and risk assessment. Your nurse practitioner reviews criteria, contraindications, risks, side effects, and alternatives, including whether a GLP-1 medication, phentermine, or neither fits.
• Options and cost. Which treatments fit, what each involves, and what it costs before you commit.
• Your plan and follow-up. Baseline measurements, a starting plan, and a regular check-in schedule to review progress, manage side effects, and adjust dosing.

Our medical weight loss program is led by Stefanie Drozd, MSN-APRN, Founder and Lead Nurse Practitioner. Express Med Spa is nurse-practitioner-led, which means a licensed nurse practitioner reviews your labs, decides whether therapy is appropriate, writes the prescription, and adjusts your dose. At our Frankfort and Mount Greenwood (Chicago) clinics, Jackie Umgelder, Lead Medical Assistant, supports patients through the program with dosing education, progress tracking, and habit reinforcement.

Enrollment is a clinical decision made with you, not a checkout page.

What Each Option Costs

At Express Med Spa, the medically supervised GLP-1 program runs $650 to $950 per month. That fee covers the medication itself, required lab work review, a comprehensive health assessment, ongoing clinical check-ins with dosage and plan adjustments, nutrition guidance, and injection training. Pricing may vary with your individualized dosage and program phase. The price is subject to change and is based on a planned consultation with staff, and financing options are available.

We do not publish a price for phentermine. Its cost is reviewed at your consultation, along with every other option, before you commit to anything.

Coverage for weight-loss medication varies widely by plan, and many plans do not cover it, so the program is generally self-pay. If you intend to submit to your plan, ask at your consultation what documentation we can provide.

If Neither Medication Is Right for You

Not being a candidate for either medication does not leave you without options. It means the plan starts somewhere else.

Lipotropic injections and vitamin B12 injections are adjuncts, not treatments that produce weight loss on their own. They can sit beside a broader eating and activity plan, and results vary. Non-invasive body contouring is a different tool again: it changes the shape of a specific area and does not reduce overall body weight, so it fits after weight loss, when one area has not followed the rest.

NIDDK also notes that some people may be able to lose weight with a lifestyle program that changes their eating and physical activity habits. Our medical weight loss options guide walks through each of these alternatives in more detail.

Where We Offer Medical Weight Loss

Medical weight loss is available at all four Express Med Spa clinics, each with its own nurse practitioner team and its own consultation schedule: Frankfort, La Grange, Shorewood, and Mount Greenwood (Chicago).

Frequently Asked Questions

Find Out Which Option Fits You

The consultation is complimentary, and it is where the choice between a GLP-1 medication and phentermine gets made. Call 877-363-3772 (La Grange: 708-847-0872) or book your complimentary consultation online.

This guide is educational and is not medical advice. It draws on our own program information and the NIDDK, MedlinePlus, and DailyMed sources linked above. Candidacy, dosing, and length of treatment are decided by our nurse practitioner team after a health assessment and lab work review. Individual results vary.