Overweight and obesity have long been significant concerns in the US. As early as the 1930s, Metropolitan Life Insurance Company pinpointed obesity as a top cause of premature death. By 1951, it was dubbed “America’s Number One Health Problem,” highlighted in books like “Fat in the Fifties: America’s First Obesity Crisis.”

As a solution, Phentermine became a popular weight loss drug and was prescribed over 50 million times in 1960.

Despite efforts to tackle the problem, recent data shows obesity rates have skyrocketed to nearly 43% from roughly 13% in 1960. To further the problem, obesity is primarily associated with type 2 diabetes, which continues to rise in prevalence and incidence, contributing significantly to human suffering and deaths.

To address these concerns, newer drugs like Ozempic have been developed. However, phentermine remains a popular choice for weight loss. This article will explore why phentermine remains relevant despite newer options like Ozempic.

Key Differences Between Ozempic and Phentermine

Cost (manufacturer’s suggested retail price)$935.77 per month$27 – $100 per month
Active ingredientSemaglutidePhentermine
Approved indicationsAdults with type 2 diabetes, including those with known heart conditions.Short-term treatment for adults with obesity or overweight with weight-related conditions.
Ease of useWeekly injectionTaken orally once a day
EffectivenessAfter 68 weeks, patients on a 1.0 mg dose lost 7% of their weight.Weight reduction of up to 10% of the total body weight after 12 weeks.
Side effectsNausea, vomiting, diarrhea, abdominal pain, and constipation occurred in at least 5% of patients.Dry mouth and insomnia
Dosage and administrationBegins with a daily dosage of 0.6 mg, gradually raised to 3 mg per day within a span of 5 weeks.The 37.5 mg dosage is taken orally daily, before breakfast, or 1 to 2 hrs post-breakfast. The 8 mg strength is taken orally thrice daily, 30 minutes before meals.
Onset of actionWithin the first 4 to 5 months.Within three months.

Efficacy in Weight Loss

Studies and clinical investigations have been conducted to assess the effectiveness of Ozempic and Phentermine in promoting weight loss.

Measuring womans waist


Since Ozempic is primarily used for the management of type 2 diabetes, it hasn’t been studied specifically for weight loss. Weight loss is just an observed side effect during treatment. However, studies have looked into semaglutide, the active ingredient in Ozempic, for weight loss.

Here are some studies that demonstrated its effectiveness in weight loss:

  • A cohort study evaluated the effectiveness of semaglutide at doses of 1.7 mg or 2.4 mg per week for weight reduction in overweight or obese individuals. This study, conducted at a weight management center, involved 408 adult participants with a BMI of 27 or higher who received semaglutide injections for a minimum of three months. Findings indicated substantial weight loss at 3 and 6 months, with average decreases of 5.9% and 10.9%, respectively. More than 87% of participants achieved at least a 5% reduction in weight after six months. However, individuals with type 2 diabetes experienced slightly less weight loss.
  • In a randomized controlled trial, diabetic participants received either a weekly dose of 2.4 mg or 1.0 mg of semaglutide, or a placebo. After 68 weeks, a higher percentage of participants in the 2.4 mg group (69%) and the 1.0 mg group (57%) achieved at least 5% reduction in body weight compared to individuals within the placebo cohort.


Since the early 2000s, Phentermine has been extensively studied for its weight loss benefits. Several studies have shown its effectiveness in facilitating weight loss. Here are a few examples:

  • A study conducted in Korea with 68 obese adults examined phentermine’s efficacy and safety. Participants took either phentermine-HCl 37.5 mg or a placebo daily for 12 weeks alongside obesity therapy. Results showed that over 80% of subjects in the phentermine group achieved weight reductions of 5% or more, with more than half achieving reductions of 10% or greater. Moreover, there was no significant variations in blood pressure between the groups, suggesting phentermine’s safety.
  • Researchers studied 795 obese patients from 30 primary care centers in Korea from September 2006 to November 2007. Patients were monitored for safety and effectiveness at 4-, 8-, and 12-week intervals. Of the 711 patients assessed for effectiveness, 45.6% lost at least 5% of their body weight. On average, patients lost around 3.8 kilograms.

Side Effects

It’s important to weigh the possible adverse reactions associated with Ozempic and Phentermine.


Common adverse effects linked with the usage of Ozempic include:

  • Nausea
  • Vomiting
  • Diarrhea
  • Abdominal pain
  • Constipation

These reactions manifested in over 5% of patients administered Ozempic in placebo-controlled trials. Additionally, other side effects include:

  • Hypoglycemia
  • Injection site reactions
  • Increases in amylase and lipase
  • Cholelithiasis
  • Increased heart rate
  • Fatigue, dysgeusia, and dizziness
  • Other gastrointestinal adverse reactions (dyspepsia, eructation, flatulence, gastroesophageal reflux disease, and gastritis)

Furthermore, Ozempic may entail potential risks or safety concerns that users should be aware of, including:

  • Pancreatitis
  • Diabetic Retinopathy
  • Acute Kidney Injury
  • Risk of Thyroid C-Cell Tumors
  • Hypersensitivity


Despite the availability of newer medications, such as Ozempic, people still seek out phentermine in the US due to its 40-year track record of safe use without serious side effects.

Two separate studies conducted in 1968 examined the effectiveness of phentermine. Neither study reported serious side effects associated with the medication.

Another study on the effects and safety of short-term Phentermine administration. Participants were required to attend hospital visits every four weeks for obesity behavioral therapy and were instructed to report any side effects of the medication at each visit.

Those who completed the study experienced phentermine 37.5 mg side effects, including:

  • Dry mouth
  • Insomnia
  • Itching sensation
  • Temporary skin lesion on the face
  • Epigastric pain (located in the region just below the ribs) and chest discomfort

As per the guidance from Gate Pharmaceuticals, one of the companies that manufactures phentermine medications, known adverse effects are:

  • Headache
  • Diarrhea
  • Tremor
  • Dizziness
  • Unpleasant taste
  • Rapid heart rate
  • Palpitation
  • Sexual side effects
  • Urticaria
  • Changes in mood

Less common but serious side effects include:

  • Primary pulmonary hypertension (PPH), also known as idiopathic pulmonary arterial hypertension (IPAH)
  • Valvular heart disease
  • Hypersensitivity

No symptoms related to these events were reported during the study period. This may be attributed to the self-reporting method for side effects experienced during study participation rather than relying solely on a side effects list provided.

Additional precautions regarding the use of phentermine have been outlined in its prescribing information. These include:

  • Impaired task performance
  • Abuse and dependence risk
  • Alcohol interaction
  • Use in patients with hypertension
  • Diabetes medication interaction
  • Withdrawal risk

Active Ingredient and Mechanism of Action

Both Ozempic and Phentermine can aid in weight loss. However, their mechanisms of action vary significantly.

Gears and Pills


Semaglutide, the active component of Ozempic, falls under the category of medications known as GLP-1 receptor agonists. These drugs emulate the functions of a hormone named glucagon-like peptide-1 (GLP-1), which occurs naturally in our bodies following food consumption.

When GLP-1 activates its receptors in pancreatic cells, it triggers insulin release, thereby reducing blood sugar levels. At the same time, GLP-1 receptors in the liver slow down glucose production, helping regulate blood sugar.

GLP-1 receptors are also present in the gastrointestinal tract, where they slow stomach emptying and curb appetite. This mechanism aids in controlling food intake and promoting feelings of fullness after meals.


Phentermine, classified as a sympathomimetic amine anorectic, is a central nervous system stimulant. This means it increases activity in certain parts of the brain.

While Ozempic activates GLP-1 receptors, Phentermine acts at the trace amine-associated receptor 1 (TAAR1) site. By acting on TAAR1, phentermine stimulates the release of neurotransmitters such as norepinephrine (noradrenaline) and epinephrine (adrenaline).

These neurotransmitters play a role in the body’s “fight or flight” response and trigger several effects that collectively contribute to weight loss:

  • Elevated heart rate and blood pressure: Heightened cardiovascular activity requires additional energy expenditure, contributing to calorie burning.
  • Metabolic boost: Stimulating metabolic processes increases basal metabolic rate (BMR). A higher BMR implies that the body expends more calories while at rest.
  • Increased alertness: Enhanced alertness and energy levels increase physical activity, further contributing to calorie expenditure.
  • Decreased appetite: Norepinephrine release during stress prompts the activation of a1-adrenoreceptors, which then suppress eating.

Approved Indications

Ozempic and Phentermine were developed for specific purposes through clinical trials, leading to their unique approved indications.


In December 2017, the FDA approved Ozempic as an accompaniment to diet and exercise for adults with type 2 diabetes for the regulation of blood sugar levels.

Ozempic pens with a dosage strength of 1.0 mg.

The approval was grounded on findings from Phase 3a clinical trials with 8,000+ adults with type 2 diabetes. Ozempic notably lowered A1c levels compared to a placebo and other diabetes medications like sitagliptin and exenatide extended-release. A1c levels refer to the average blood sugar levels over 2-3 months.

The FDA approved a new indication for Ozempic in 2020 based on findings from the SUSTAIN 6 trial. This approval addresses the reduction of major adverse cardiovascular events (MACE) in adults diagnosed with type 2 diabetes and pre-existing heart conditions.

In the trial, Ozempic demonstrated a significant 26% reduction in MACE risk compared to placebo over a 2-year period.


In 1959, the FDA approved phentermine for short-term use (less than 12 weeks) in treating exogenous obesity, which refers to obesity that stems from external factors like diet, lifestyle, or certain medical conditions or medications.

Additionally, the US FDA approved the combination of phentermine and extended-release (ER) topiramate drugs (Qysmia) in 2012 to treat obesity. Topiramate, an anticonvulsant with weight loss effects, was discovered in 1979 but was not released commercially until 1996.

Phentermine and phentermine/topiramate drugs are approved for use with diet and exercise in adults with the following conditions:

  • Obese individuals (BMI ? 30 mg/kg²)
  • Overweight individuals (BMI ? 27 mg/kg²) with at least one weight-related comorbidity like high blood pressure, type 2 diabetes, or abnormal lipid levels.

In July 2022, phentermine/topiramate was approved in the US for chronic weight management in pediatric patients aged 12 years and older. It’s indicated as an adjunct to a reduced-calorie diet and increased physical activity in individuals with a BMI at or above the 95th percentile, adjusted for age and sex.

Short History of Combination Drugs “Fen-Phen” and “Dexfen-Phen”

In July 1992, a combination drug containing fenfluramine and phentermine (Fen-Phen) was introduced and gained popularity. As the drug gained momentum, another combination, known as Dexfen-Phen, was introduced to combat obesity more effectively. Dexfenfluramine is a more effective form of fenfluramine.

Although the FDA approved fenfluramine, dexfenfluramine, and phentermine for separate use, the combination was not approved as a single drug. Yet, these drug combinations received significant media attention and were widely seen as a “magic pill,” with approximately six million Americans using Fen-Phen or Dexfen-Phen.

In September 1997, they were withdrawn from the market after two separate studies linked Fen-Phen and Dexfen-Phen to serious side effects, including heart disease, cardiac valvular disease, primary pulmonary hypertension, and cardiac fibrosis.

On the other hand, phentermine alone has not been linked to these conditions. This led researchers to compare the efficacy of phentermine and the drug combinations on weight loss.

A 2003 study found no significant difference in weight loss rates between phentermine alone and Phen-Fen. Both showed comparable results at week 12 for women (7.4% in the Phen group and 8.7% in the Phen-Fen group) and men (7.8% vs. 8.2%).

Dosage and Administration

Ozempic and Phentermine have different dosages and administration methods. Ozempic is administered via subcutaneous injection, while Phentermine is taken orally.


Treatment with Ozempic starts with a 0.25 mg injection once weekly for four weeks, then increases to 0.5 mg once weekly.

If further blood sugar regulation is necessary after at least four weeks on 0.5 mg, the dose may escalate to 1 mg administered once weekly. Ozempic’s maximum weekly dose is 2 mg.

It is recommended that Ozempic be administered once weekly on the same day, at any time, regardless of meals. If altering the injection day, ensure a minimum of a 2-day gap between doses.

If a dose is missed, it should be administered within five days. Otherwise, the regular once-weekly dosing schedule should be resumed with the next scheduled dose.


Phentermine is available by prescription under various brand names, including Adipex-P, Lomaira, and Qysmia. Each has different dosage strengths and administration instructions.


Adipex-P contains 37.5 mg phentermine hydrochloride. Both the Adipex-P tablet and capsule are taken orally once daily, either before breakfast or 1 to 2 hours after breakfast. The dosage for the tablet might be reduced to 18.75 mg (half a tablet) once or twice daily.


Phentermine comes in a smaller 8 mg tablet called Lomaira. It is usually taken orally three times daily, 30 minutes before meals. Some may require only 4 mg (half a tablet) for any or all doses.

Qysmia (Phentermine/Topiramate)

This drug comes in oral capsules with different strength combinations of phentermine mg/topiramate mg ER, including:

  • 3.75 mg/23 mg
  • 7.5 mg/46 mg
  • 11.25 mg/69 mg
  • 15 mg/92 mg

Here’s the administration of Phentermine/Topiramate:

DosageDosing scheduleEvaluation
Starter dose (weeks 1-2)One Qsymia 3.75 mg/23 mg capsule each morning for the first two weeks.
Recommended dose (weeks 3-12)On the first day of week 3, individuals will start the recommended dose, taking one Qsymia 7.5 mg/46 mg capsule each morning.Adult and pediatric patients may continue at this dose if 3% or greater weight loss is achieved after 12 weeks. Otherwise, discontinue or escalate the dose.

Consider a dosage reduction for pediatric patients who experienced weight loss exceeding 2 lbs/week.

Titration dose (weeks 13-14)If the doctor increases the dose, the patient will take one Qsymia 11.25 mg/69 mg on the first day of week 13 until the end of week 14.
Top dose (weeks 15 or more)On the first day of week 15, the patient will take monthly prescriptions of Qsymia 15 mg/92 mg.Discontinue use if 5% weight loss isn’t achieved after 12 weeks.

It’s advised to take it in the morning to avoid insomnia.


Phentermine is widely prescribed due to its cost-effectiveness compared to newer drugs like Ozempic, which costs $935.77 monthly without insurance and lacks generic alternatives.

On the other hand, Phentermine is accessible as a generic medication, making it more economical compared to its brand-name counterpart. Adipex-P typically costs around $100 for a 30-day supply, while its generic version costs $42 without insurance. Another brand, Lomaira, is even more economical at approximately $27 for 30 daily tablets. Additionally, individuals can utilize coupons and discount cards to reduce costs further.

Qsymia (Phentermine/Topiramate) has a retail price of $250.46, according to GoodRx. However,  savings cards are available on Qysmia’s official website. Patients with commercial insurance can receive $65 off while cash-paying patients can get $70 off.

Several programs are also available to alleviate the financial burden of getting Ozempic without insurance. These include:

  • Novo Nordisk Patient Assistance Program (PAP)
  • Patient Access Network Foundation (PAN)
  • Ozempic Savings Card
  • Diabetes Savings Offer Program

Another option is to buy Ozempic from Canadian pharmacies like Pharma Giant for savings of up to 90% on prescription medications. Customers can also enjoy additional discounts and offers, especially when ordering larger quantities.

New customers can avail themselves of a 10% discount on their first order using the coupon code FIRST10. Pharma Giant ensures expedited delivery within 3-5 business days for added convenience, and stringent measures are implemented to package temperature-sensitive medications securely.

Here’s a price comparison of popular weight loss drugs available on Pharma Giant versus those offered by online pharmacies in the US:

Brand NamePharma GiantWalgreensCVS PharmacyRite Aid

Onset of Action

Ozempic is intended for long-term use. It takes 4 to 5 weeks to reach a steady level in the body. Full effects in managing type 2 diabetes are usually noticeable after at least eight weeks of treatment, with weight loss occurring within the first 4 to 5 months.

In contrast, Phentermine is prescribed for short-term use and begins working relatively quickly.  It can reduce a person’s weight by up to 5% of their overall body weight within three months.

Phentermine/topiramate, a combined drug, is approved for longer-term use. Weight loss may become noticeable within the first 8 to 12 weeks of treatment.

For more details on the duration of weight loss with Ozempic. Find additional information here.


Ozempic and Phentermine are distinct medications serving different purposes. Ozempic (semaglutide) is prescribed for managing type 2 diabetes. It works by mimicking the action of the hormone glucagon-like peptide-1 (GLP-1).

Meanwhile, Phentermine serves as a short-term adjunct to weight loss programs, including diet, exercise, and behavioral modifications, primarily for obese individuals. It acts as an appetite suppressant by stimulating the secretion of particular chemicals in the brain.

Common side effects of Ozempic include nausea and decreased appetite, while Phentermine may cause increased heart rate and insomnia. Despite their weight-related impacts, these medications differ in their mechanisms, uses, and risks.

Frequently Asked Questions

How do I choose between Ozempic and Phentermine?

The choice between Ozempic and Phentermine often depends on various factors such as side effect tolerance, cost, contraindications, medical history, weight loss goals, and existing health conditions. In terms of weight loss, studies suggest that for weight loss in adults with overweight and obesity, medications like phentermine/topiramate and GLP-1 receptor agonists (such as Ozempic) are most effective. Among GLP-1 agonists, semaglutide stands out as particularly potent. Cost is also a significant consideration, as weight-loss drugs can be expensive. Check with your insurance provider regarding coverage and duration of coverage for the medications under consideration.

Can you take Ozempic and Phentermine together?

Although the two medications work in different ways to help individuals lose weight, it’s advisable to avoid taking them simultaneously. There hasn’t been any specific study conducted on the concurrent use of phentermine and Ozempic, so it’s unclear whether it’s safe or beneficial to use them together.

Who shouldn’t take Ozempic or Phentermine?

Ozempic should not be taken by individuals with a personal or family history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN 2). It’s also not recommended for those with severe gastrointestinal disease, such as gastroparesis. Additionally, people with a history of hypersensitivity to semaglutide or any of the ingredients in Ozempic should avoid it.

Phentermine is contraindicated in individuals with a history of cardiovascular disease (e.g., coronary artery disease, heart rhythm problems, congestive heart failure), uncontrolled high blood pressure, hyperthyroidism, glaucoma, or a history of drug abuse or dependence. It’s also not recommended for pregnant women, nursing mothers, or individuals with a history of agitation, anxiety, or significant agitation.

Which is better for weight loss?

Semaglutide and phentermine are both effective for weight loss, but limited direct comparison exists between them. Some research suggests that injectable semaglutide may result in more weight loss than phentermine. In a 2021 study, participants using semaglutide showed greater reductions in body weight compared to those using other approved weight loss medications, including phentermine. However, it’s important to note that only Wegovy is FDA-approved for weight loss, while Ozempic can be prescribed off-label for this purpose.

What weight loss pill is closest to Phentermine?

The weight loss pill closest to Phentermine in terms of its mechanism of action and efficacy is phentermine-topiramate, marketed under the brand name Qsymia. This drug combines low doses of phentermine with an extended-release form of topiramate, which is an anticonvulsant medication that also helps with weight loss. Phentermine works as an appetite suppressant, while topiramate might aid in weight loss by enhancing sensations of fullness and reducing cravings.

Can you lose belly fat on Ozempic?

Yes, a study funded by Novo Nordisk found that semaglutide decreased visceral fat and overall fat mass in nearly 2,000 overweight or obese adults without diabetes. Visceral fat is the type that accumulates in the belly.

What are other alternatives to Ozempic?

Alternative medications to Ozempic for managing type 2 diabetes include Trulicity (dulaglutide), Mounjaro (tirzepatide), and Rybelsus (semaglutide). In terms of weight loss, alternatives include Wegovy (semaglutide) and Saxenda (liraglutide). Each drug offers distinct approaches to addressing diabetes and obesity, catering to individual preferences and requirements.

Why am I not losing weight on Phentermine?

Over time, tolerance can develop to phentermine’s weight-loss effects, potentially diminishing its effectiveness. In such cases, drug discontinuation may be necessary under medical guidance.

Is it possible to regain weight after discontinuing semaglutide use?

Yes. In a study involving nearly 2,000 participants, published in 2022, findings revealed that individuals who discontinued the use of 2.4 mg doses of semaglutide had regained approximately two-thirds of the weight they initially lost within one year after stopping the treatment.

Is it possible to regain weight after discontinuing phentermine use?

Yes. Although phentermine effectively suppresses appetite, it does not affect the body’s metabolism or genetics, which collectively account for over 80% of body weight regulation. While individuals in placebo-controlled trials experience weight loss, these outcomes are typically temporary. Specifically, within one year after discontinuing treatment, approximately one-third of users regain the weight they initially lost.


Becker Law Office. History of Fen-Phen and Redux®. Retrieved from https://beckerlaw.com/kentucky-dangerous-drug-lawyer/diet-drugs/history/

Dhillon, S. (2022, Nov). Phentermine/Topiramate: Pediatric First Approval. PubMed. https://pubmed.ncbi.nlm.nih.gov/36059008/

Drugbank Online. (2005, Jun). Phentermine. Retrieved from https://go.drugbank.com/drugs/DB00191

FDA. (2012, Jan). Adipex-p (phentermine hydrochloride) capsules label. Retrieved from https://www.accessdata.fda.gov/drugsatfda_docs/label/2012/085128s065lbl.pdf

FDA. (2012, Jul). Highlights Of Prescribing Information of Qysmia. Retrieved from

FDA. (2017, Dec). Highlights Of Prescribing Information of Ozempic. Retrieved from https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/209637lbl.pdf

Fryar, C.D., et al. (2021, Jan). Prevalence of Overweight, Obesity, and Severe Obesity Among Adults Aged 20 and Over: United States, 1960–1962 Through 2017–2018. CDC. https://www.cdc.gov/nchs/data/hestat/obesity-adult-17-18/obesity-adult.htm#1

Ghusn et al., (2022, Sep 19). Weight Loss Outcomes Associated With Semaglutide Treatment for Patients With Overweight or Obesity. NCBI. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9486455/

Johns Hopkins University Press. (2019, Mar). Fat in the Fifties. Retrieved from https://www.press.jhu.edu/books/title/12003/fat-fifties

Johnson, D.B., & Quick, J. (2023, Mar). Topiramate and Phentermine. NLM-StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK482165/

Khan, M.A.B., et al. (2020, Mar). Epidemiology of Type 2 Diabetes – Global Burden of Disease and Forecasted Trends. PubMed Central. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7310804/

LiverTox. (2020, Jun). Phentermine. NCBI. https://www.ncbi.nlm.nih.gov/books/NBK547916/

Li, Z., et al. (2003, Jul). Body weight loss with phentermine alone versus phentermine and fenfluramine with very-low-calorie diet in an outpatient obesity management program: a retrospective study. NCBI. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4053043/

NovoCare. (2023). Find out the cost for Ozempic. Retrieved from https://www.novocare.com/diabetes/products/ozempic/explaining-list-price.html

Ojeniran et al. (2021, Nov). Semaglutide for weight loss. CFP. https://www.cfp.ca/content/67/11/842

PR Newswire. (2017, Dec 5). Novo Nordisk Receives FDA Approval of OZEMPIC® (semaglutide) Injection For the Treatment of Adults with Type 2 Diabetes. Retrieved from  https://www.prnewswire.com/news-releases/novo-nordisk-receives-fda-approval-of-ozempic-semaglutide-injection-for-the-treatment-of-adults-with-type-2-diabetes-300567052.html

Qysmia. (2023, Dec). How to take Qsymia. Retrieved from https://qsymia.com/patient/resources/taking-qsymia

Reyhanditya, D., et al. (2022, Apr). Restraint Stress Impacts on Behavioral Changes and Adrenal and Kidney Tissue Histopathology of Adult Mice. ResearchGate. https://www.researchgate.net/publication/359975950_Restraint_Stress_Impacts_on_Behavioral_Changes_and_Adrenal_and_Kidney_Tissue_Histopathology_of_Adult_Mice

The Surgeon General’s Vision for a Healthy and Fit Nation. (2010). Background on Obesity. NCBI. https://www.ncbi.nlm.nih.gov/books/NBK44656/

USAFacts Team. (2023, Mar). US obesity rates have tripled over the last 60 years. Retrieved from

Wilding, J.P.H., et al. (2021, May). Impact of Semaglutide on Body Composition in Adults With Overweight or Obesity: Exploratory Analysis of the STEP 1 Study. PubMed Central.