Phentermine vs. Wegovy: Which one is the best weight loss drug?

Key points

• Phentermine is a daily pill prescribed as a short-term appetite suppressant
• Wegovy (semaglutide) is a weekly injection that mimics natural hormones to support longer-term weight management
• In clinical trials, Wegovy generally leads to greater weight loss than phentermine
• Though affordable, phentermine's stimulant properties restrict it to short-term use

Prescription weight-loss medications have changed significantly in recent years. Newer drugs like Wegovy (semaglutide) have reshaped long-term obesity treatment.

Meanwhile, older medications such as phentermine remain widely prescribed because they are inexpensive, familiar to clinicians, and often required by insurance plans as a first step.

Although both are used for weight loss, phentermine and Wegovy work in very different ways. And these differences matter when weighing benefits, risks, and next steps.

How do they work?

These medications affect your body in different ways.

Phentermine supports weight loss primarily by reducing hunger signals in the brain. It acts as a stimulant on your central nervous system. Phentermine triggers the release of norepinephrine in your brain, creating a "fight or flight" response that naturally suppresses appetite and boosts energy.

Wegovy (semaglutide) works through a completely different mechanism. It mimics GLP-1, a natural hormone that signals fullness to your brain. Wegovy helps reduce appetite and you feel satisfied with smaller portions. It also slows digestion, keeping food in your stomach longer so you stay full for hours after eating.

Which one is better for weight loss?

Wegovy has been shown to provide a greater average weight loss in clinical trials, although weight loss results vary from person to person.

Phentermine weight loss results

In clinical studies, people taking phentermine typically lost about 5% of their body weight.

Some saw better results, but the effects often plateau after a few months as the body builds tolerance to the stimulant effects.

Wegovy weight loss results

People taking Wegovy lost an average of nearly 15% of their body weight over 68 weeks, with more sustained results compared to phentermine.

Phentermine or Wegovy: How to choose?

Beyond the clinical trial numbers, several practical factors influence which medication might work better for your situation:

• Medical history: Certain health conditions affect how well your body tolerates stimulants versus GLP-1 medications
• Cost and insurance: These medications can be expensive, and coverage varies widely between plans
• Administration method: Phentermine is a daily pill, while Wegovy involves a weekly injection, which some people may find inconvenient or uncomfortable
• Treatment duration: The FDA approves phentermine only for short-term use (up to 12 weeks), making it suitable for initial weight loss. Some people start with phentermine and transition to Wegovy for longer-term management

"The best approach aligns with your specific health profile, budget, and lifestyle," explains Gia Eapen, MD. "Discussing these factors with your healthcare provider helps determine which option fits your situation."

Which one quiets "food noise" better?

"Food noise" is the constant mental chatter about food. It is the obsessive planning of your next meal. It is the inability to stop thinking about fried foods or the voice in your head urging you to eat a bag of Oreos.

Wegovy

Wegovy helps quieten the food noise and reduce cravings for many people.

GLP-1 medications like Wegovy work on multiple brain pathways involved in appetite and reward. They act on areas of the brain that control hunger signals and may reduce the brain's reward response to food, making highly palatable foods less appealing.

Research shows that people taking Wegovy (semaglutide) often report less frequent and intense food-related thoughts, which helps them stick to their eating plans.

However, some people continue to struggle with binge eating even when they take semaglutide (Wegovy’s star ingredient). This is because disordered eating patterns like binge eating are often driven by mental health conditions.

Phentermine

Phentermine is a stimulant appetite suppressant and can reduce hunger cravings. It works by releasing neurotransmitters like norepinephrine and dopamine in the brain's hypothalamus region, which controls hunger. Some people may feel less preoccupied with food while taking it.

Studies show phentermine can reduce cravings for fats and sweets. However, it does not specifically address reward or addiction pathways the way GLP-1 medications do.

The underlying habits and urges to eat can still remain, especially once the medication wears off or is stopped.

Because tolerance develops over time, the appetite-suppressing effects may weaken after several weeks or months of use.

Which weight loss drug costs less?

Phentermine is more cost-effective than Wegovy as it is a generic drug. The cash price at most US pharmacies is typically between $8 and $25 per month, making it affordable for most eligible individuals. Many people even opt to pay out of pocket to avoid insurance paperwork.

While Phentermine may be cheaper, recent price changes for Wegovy have made it more accessible than before.

Reduced Wegovy pricing

Wegovy used to be very expensive, but Novo Nordisk (the manufacturer) introduced discounted pricing effective on November 17th, 2025.

• People who pay out of pocket or without insurance can now get Wegovy for $349 a month, down 30% from the previous $499.
• First-time patients without insurance can obtain starter doses (0.25 mg and 0.5 mg) for $199 per month for the first two months.
• Those with private insurance plans that include Wegovy coverage may qualify for assistance programs that could bring their monthly expense down to $0.

The manufacturer plans to offer these reduced prices through March 31st, 2026.

Navigating insurance ‘step therapy’ for weight loss

Insurance rules can affect which medication you can access first.

Some plans use ‘step therapy,’ which requires trying lower-cost or preferred medications like phentermine before they will cover newer, expensive options like Wegovy. The exact requirements vary by insurer and plan.

Calling your health plan or pharmacy benefits manager helps you understand your specific coverage and any step-therapy rules that may apply.

Which one is easier to take: a daily pill or a weekly injection?

Your personal preferences, lifestyle, and how your body responds to each medication influence which administration method works better for you.

Phentermine (The daily pill)

Phentermine is an oral medication typically taken once a day in the morning, either before breakfast or 1 to 2 hours after. It requires no special equipment.

However, since it is a stimulant, it needs to be taken every single day in the morning to maintain effectiveness.

Wegovy (The weekly injection)

Wegovy requires thinking about your medication only once a week. The device is an autoinjector pen where you don't see the needle. You simply press it against your skin and wait for the click.

The weekly injection involves using a small needle, which can be a mental barrier for some people. The pens need to be stored in the refrigerator, though they can be kept at room temperature for a limited time. This adds some extra planning, especially for frequent travelers.

Discussing your daily routine with your doctor can help you learn which option may work better for you.

Side effects comparison

Phentermine and Wegovy work on different systems in the body, so their side effect profiles are distinct.

Phentermine side effects

Phentermine is a stimulant, so side effects are often related to energy and the nervous system. Common side effects include insomnia, restlessness, dizziness, and dry mouth. It can also cause a fast heart rate.

More serious concerns include increased blood pressure. Doctors typically do not recommend it for people with heart disease. Phentermine is a controlled substance with potential for dependence, which is why the FDA approved it only for short-term use.

Wegovy side effects

Nausea is the most common complaint with Wegovy. Other digestive side effects include vomiting, diarrhea, constipation, or stomach pain. These digestive issues are usually strongest when first starting the medication and often subside over time.

More serious warnings include potential thyroid tumors based on rodent studies, as well as risks of pancreatitis.

Final thoughts: Phentermine vs. Wegovy

Phentermine and Wegovy are two different paths to the same goal.

Phentermine is affordable and works quickly. It's approved only for short-term use and comes with stimulant side effects. 

Wegovy provides a longer-term solution with larger average weight loss in clinical trials. It requires weekly injections and may involve managing digestive issues.

The choice depends on several factors, including your medical history, particularly your heart health. Budget and insurance coverage also play a role.

Your healthcare provider can evaluate your specific profile and help you find the safest and most effective option for your situation.

Frequently Asked Questions (FAQs)

Can I switch from phentermine to Wegovy?

Switching between these medications may be possible depending on your individual situation. Phentermine is only approved for short-term use (up to 12 weeks), while Wegovy is used for longer-term management.

Whether switching is appropriate depends on your weight loss results, health conditions, insurance coverage, and eligibility criteria for each medication. Your healthcare provider can evaluate your circumstances and determine if this transition makes sense for you.

Why is phentermine only for short-term use?

Phentermine is a Schedule IV controlled substance. It has a chemical structure similar to amphetamines. This carries a risk of potential abuse. The body also builds a tolerance to it. The stimulant effects diminish over time after a few months. That is why the FDA limits use to 12 weeks.

Does Wegovy burn fat or just suppress appetite?

Wegovy primarily works by suppressing appetite. It mimics the GLP-1 hormone, which helps you feel full longer and slows digestion. This makes it easier to eat fewer calories, which leads to fat loss. Some research suggests it may also slightly increase metabolism, but appetite suppression is the main mechanism.

Does phentermine or Wegovy act faster for weight loss?

Phentermine typically works faster, initially. Most people feel appetite suppression within the first hour and may see weight loss within a couple of weeks.

Wegovy takes longer. It requires a gradual dose increase over several months, with minimal weight loss in the first month and more significant results appearing later.

Weight loss results vary widely and depend on factors like diet, exercise, metabolism, and starting weight.

Can I take phentermine and Wegovy together for faster results?

Eapen, MD, says, “Combining phentermine and Wegovy is not recommended. The safety and effectiveness of using both medications together have not been well studied in clinical trials. Both drugs can affect heart rate and blood pressure, so taking them together could amplify cardiovascular side effects.”

If one medication is not providing the results you're hoping for, talk with your doctor about adjusting your treatment plan rather than adding another medication on your own.

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The views expressed by authors and contributors of such content are not endorsed or approved by Fay and are intended for informational purposes only. The content is reviewed by Fay only to confirm educational value and audience interest. You are encouraged to discuss any questions that you may have about your health with a healthcare provider.