We know that choosing the right weight loss medication can feel like a huge challenge—especially when there are so many options like phentermine and semaglutide to consider. 

You’re probably asking yourself: Which one will work for me? Will it be effective? What about side effects?

Here’s the short answer: Phentermine is a stimulant that helps curb appetite for short-term weight loss, while semaglutide works by regulating hunger and metabolism, providing a more sustainable, long-term solution.

The longer answer? Well, we’ll walk you right through it in this guide. 

We explain the key differences between these two medications—how they work, what to expect in terms of results, their side effects, and costs—so you can make a well-informed decision that fits your weight loss journey.

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What is Phentermine?

Phentermine is a prescription weight loss medication that works as an appetite suppressant. It belongs to a class of drugs called sympathomimetic amines, which stimulate the central nervous system to reduce hunger. It’s typically prescribed for short-term use (up to 12 weeks) as part of a doctor-supervised weight loss plan.

Phentermine is often recommended for individuals with a BMI of 30 or higher (or 27+ with weight-related conditions like diabetes or hypertension). While it can be effective for rapid weight loss, it comes with potential side effects and is not suitable for everyone, especially those with heart conditions or high blood pressure.

What is Semaglutide?

Semaglutide is a GLP-1 receptor agonist, a type of medication that mimics a natural hormone to help regulate blood sugar, appetite, and digestion. Originally developed to treat type 2 diabetes, it is now FDA-approved for chronic weight management under brand names like Wegovy and Ozempic.

Unlike phentermine, which works as a stimulant, semaglutide slows digestion and reduces hunger, leading to gradual and sustained weight loss. 

It is typically prescribed for individuals with a BMI of 30 or higher (or 27+ with weight-related conditions) and is administered via a weekly injection, oral semaglutide, or semaglutide drops, offering flexibility based on patient preference. While highly effective, it may cause gastrointestinal side effects like nausea and stomach discomfort.

The Differences Between Phentermine and Semaglutide

Phentermine and semaglutide differ in how they work, their effectiveness, side effects, and cost. Below is a detailed comparison to help you understand which option might be best for you. We'll also address common myths about semaglutide, such as misconceptions about how it affects metabolism and long-term weight management.

Key Differences

Here’s a quick breakdown of the main differences between phentermine and semaglutide:

How Phentermine Works

Phentermine is a stimulant medication that helps curb appetite by activating the central nervous system. This results in reduced hunger, leading to quick weight loss over a short period. Since it only targets appetite, it doesn't directly impact metabolism or fat storage, meaning that weight loss may not be as sustainable once the medication is stopped. It's often prescribed for short-term use (up to 12 weeks) to give users a jumpstart in their weight loss journey.

How Semaglutide Works

Semaglutide, on the other hand, is a GLP-1 receptor agonist. It mimics a natural hormone that helps regulate appetite and blood sugar levels, slowing down digestion and making you feel full for longer. As a result, it supports gradual, sustained weight loss over time. 

Unlike phentermine, which is typically used for quick results, semaglutide can be prescribed for long-term use as part of a comprehensive weight management plan.

Duration of Use

Phentermine is designed for short-term use, typically prescribed for up to 12 weeks. It's best suited for individuals who need quick results and are ready to implement lifestyle changes alongside medication.

Semaglutide is prescribed for long-term use, with studies showing that it can be effective for continuous weight management. It is often used in combination with a healthy diet and exercise program to help maintain weight loss over time.

Cost Considerations

Phentermine is generally more affordable than semaglutide and may not be covered by insurance for weight loss purposes. However, due to its short-term use, the overall cost may be lower for those using it temporarily.

Semaglutide is typically more expensive and may be covered by insurance if prescribed for obesity treatment. While it might cost more initially, its long-term use and effectiveness can make it a more cost-effective option in the long run for those looking for lasting weight loss results.

Comparison Table: Phentermine vs. Semaglutide

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Both medications can support weight loss, but the best option depends on your health history, weight loss goals, and lifestyle preferences.

Side Effect Comparison

Both phentermine and semaglutide come with potential side effects, though they impact the body in different ways. Below, we break down the most common side effects of each medication.

Side Effects of Phentermine

Phentermine is a stimulant that affects the nervous system, which can lead to:

• Increased heart rate and blood pressure – May not be suitable for individuals with heart conditions.
• Insomnia and restlessness – Due to its stimulant properties, it can disrupt sleep.
• Dry mouth – Common, but can be managed by staying hydrated.
• Dizziness and headaches – Typically mild but can occur, especially at the start of treatment.
• Dependency risk – As a controlled substance, there’s potential for misuse if not taken as prescribed.

Most side effects decrease over time, but some may persist, especially if taken for an extended period.

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Side Effects of Semaglutide

Semaglutide primarily affects digestion and metabolism, leading to:

• Nausea and vomiting – The most commonly reported side effect, especially when starting treatment.
• Diarrhea or constipation – Can occur as the body adjusts to the medication.
• Loss of appetite – While helpful for weight loss, it may lead to unintended undernutrition if not monitored.
• Fatigue – Some individuals report feeling more tired than usual (compounded semaglutide with B12 can help here).
• Potential risk of thyroid tumors – Though rare, studies in animals have raised concerns; discuss with your doctor if you have a history of thyroid issues.

Many of these side effects lessen over time as the body adapts, and dosage adjustments can help manage discomfort.

Which is More Effective for Weight Loss?

When comparing phentermine and semaglutide, their effectiveness depends on your weight loss goals, diet plan, and how long you plan to use the medication.

Phentermine works quickly, often leading to significant weight loss in the first few weeks. However, since it’s only approved for short-term use (up to 12 weeks), many people regain weight after stopping.

Semaglutide promotes steady, long-term weight loss, with clinical studies showing that users can lose up to 15% of their body weight over several months. Since it regulates hunger and metabolism, weight loss is often more sustainable compared to phentermine.

Which One is Right for You?

• If you need fast weight loss for a short period, phentermine may be a better option.
• If you’re looking for long-term, sustained weight loss, semaglutide is generally the more effective choice.

Your doctor can help determine the best medication based on your health history, weight loss goals, diet plan, and risk factors.

Start Your Weight Loss Journey with IVY RX

Finding the right weight loss medication is just the first step—having expert guidance makes all the difference. At IVY RX, we provide personalized weight loss solutions to help you achieve lasting results.

✔ Expert Support – Our healthcare professionals will help you determine whether phentermine or semaglutide is the best fit for your goals.
✔ Convenient Access – Get semaglutide delivered to your door with easy online consultations.
✔ Ongoing Care – We’re here to support you every step of the way with dosage guidance, progress tracking, and expert recommendations through our online program.

Ready to take control of your weight loss journey? Find your treatment today with IVY RX.

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FAQs

Where Do You Inject Semaglutide?

Semaglutide is injected subcutaneously (under the skin), typically in the abdomen, thigh, or upper arm. It’s important to rotate injection sites to avoid irritation. Your healthcare provider can show you the best technique for safe and effective administration.

How Long Does Phentermine Stay in Your System?

Phentermine has a half-life of about 20 hours, meaning it can stay in your system for up to four days. However, individual factors like metabolism, hydration, and kidney function can affect how quickly it’s eliminated.

Can Phentermine Cause Constipation?

Yes, constipation is a common side effect of phentermine. This happens because it suppresses appetite, leading to reduced food intake and slower digestion. Staying hydrated and increasing fiber intake can help prevent this issue.

Will I Experience Phentermine Withdrawal?

Some people experience mild withdrawal symptoms when stopping phentermine, such as fatigue, increased appetite, or mood changes. This is more common in long-term users or those who abruptly stop taking the medication. Gradually tapering off under medical supervision can help minimize withdrawal effects.

Can You Take Phentermine with Semaglutide Together?

Combining phentermine and semaglutide is sometimes prescribed under medical supervision, but it’s not recommended for everyone. Since both medications affect appetite and weight loss, using them together may increase side effects like nausea, dizziness, or heart palpitations. Always consult your doctor before combining weight loss medications.

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