Phentermine is a prescription appetite suppressant used for the short-term treatment of obesity [1, 2]. It is utilized in combination with behavioral changes such as eating a healthier diet and exercising regularly to promote weight loss.
Phentermine hydrochloride (phentermine HCL) is a Schedule IV drug under the United States’ Controlled Substances Act and the international Convention on Psychotropic Substances .
This medication is a sympathomimetic amine anorectic and it functions as a central nervous system (CNS) stimulant . Its active ingredient, phentermine hydrochloride, promotes a stress response similar to the “fight or flight” reaction that is typically generated during times of stress and it also reduces hunger . In addition, phentermine stimulates the release of the neurotransmitter, adrenaline (epinephrine), into the body and this stimulates the breakdown of stored fat. Therefore, phentermine promotes weight loss by reducing the appetite and increasing energy .
Phentermine can produce a wide variety of side effects, including serious complications such as heart and lung problems. However, most people only experience minor reactions. The most common side effects include dry mouth (xerostomia), trouble sleeping (insomnia), constipation, and headache .
Skip to the Side Effects section to learn more about the side effects.
In the early 1980s, Dr. Michael Weintraub and his colleagues at the University of Rochester published a paper detailing the effectiveness of an off-label combination of fenfluramine and phentermine for weight loss . This cocktail was commonly known as “Fen-Phen” and doctors regularly prescribed the two medications together. However, in 1997 clinical findings were published which demonstrated that the powerful combination increased patients’ risk of heart valve disease and fenfluramine, the culpable substance, was withdrawn soon thereafter . However, phentermine has remained available for prescription and sale.
Phentermine supports weight loss by suppressing the appetite and boosting energy.
On the most basic level, weight loss is a matter of creating an internal environment in which the body is expending energy in a manner that burns more calories than are being consumed. Accordingly, this medication helps you eat less and move more, both of which are processes that cause the body to expend more energy in the form of fat burning. As the amount of fat-burning increases so does weight loss, and phentermine produces these effects by acting as a central nervous system stimulant.
Phentermine boosts your weight loss efforts, but it’s still up to you to eat well, to incorporate doctor-approved physical activities into your daily routine, and to make healthy lifestyle choices. Committing to sustainable behavioral changes will not only maximize your weight loss while taking phentermine, but will also help you keep the weight off after your prescription comes to an end!
Phentermine diet pills have one active ingredient: phentermine. Most pills contain phentermine HCL and Ionamin (a name brand form) contains phentermine resin. However, different forms (capsules, tablets, etc.) and brands of phentermine contain distinct inactive ingredients. These inactive ingredients include fillers, dyes, and binding agents.
Phentermine HCL is a sympathomimetic amine, which has a chemical structure similar to amphetamines . However, phentermine is NOT an amphetamine
More specifically, you can see in the image below that the only difference between the two substances is the methyl group (CH3) on the phentermine molecule, which takes the place of the single hydrogen (H) atom in the amphetamine.
Similar to amphetamines, phentermine works by stimulating your central nervous system. This makes it highly effective at promoting weight loss, but also makes it potentially-addictive and dangerous if not used as directed. However, phentermine is a Schedule IV drug while most amphetamines are Schedule II drugs, which indicates that this prescription medication has a lower addictive potential and is medically-recognized for treatment purposes.
Due to the structural similarities, phentermine may also show-up as a false-positive for amphetamines on standard drug screens . Therefore, it is critical that you provide a valid doctor’s prescription if you are requested to undergo drug testing. Phentermine is legal when it is used for weight loss under a doctor’s supervision, but you should always be prepared to show a current and valid prescription. If a false-positive result shows up on a drug test, more specific testing distinguishes between this prescription medication and other [illegal] drugs.
The half-life of phentermine HCL is 16-31 hours (average 20 hours), and this means that most people would not test positive for the chemical 4-7 days after phentermine use is discontinued . However, this time period varies from person-to-person. Factors that may influence how long the medication stays in your system include: urinary pH, the duration of use, and the daily dosage.
Patients with a BMI ≥ 30 kg/m2, or a BMI ≥ 27 kg/m2 in addition to another weight-related condition, may be eligible for prescription weight loss medication. BMI refers to body mass index.
Phentermine is designed to be an adjunct treatment for generally-healthy patients who are overweight or obese and have not lost sufficient weight through diet and exercise alone. For this reason, phentermine is specifically prescribed for the treatment of exogenous obesity, which is obesity that is caused by external factors such as eating too much or exercising too little.
Phentermine is not appropriate or safe for everyone. It is critical that you inform your doctor of all current and past medical conditions, as well as any current or recent medications and supplements you may be taking. Consuming phentermine may lead to serious complications for people who have certain medical conditions (e.g. hyperthyroidism, glaucoma) or those who are taking other medications.
→ For a more comprehensive list of precautions and contraindications, please click here.
REMINDER: Only a medical doctor can evaluate if phentermine is appropriate and safe for you.
Phentermine produces a range of potential side effects. These reactions range from relatively mild to very severe.
While most patients take this mediation without experiencing any issues, phentermine can cause serious side effects for some people. These reactions include potentially-fatal heart and lung problems.
Call emergency medical services or contact your doctor immediately if you experience any of the following reactions:
→ For a more comprehensive list of phentermine side effects, please click here.
Thankfully, most patients experience only minor to moderate side effects.
The most common side effects of phentermine are dry mouth (xerostomia), trouble sleeping (insomnia), constipation, and headache. Additional reactions that may occur include: a change in sexual desire, diarrhea, dizziness, mood changes (e.g. “phen rage”), nausea or vomiting, rapid (racing) heartbeat, rash, stomach pain, tiredness, and an unpleasant taste in the mouth.
Below are the results of a poll that assessed the incidence of common side effects:
Phentermine is available in doses ranging from 8 mg to 37.5 mg in most countries.
The dose that is prescribed for you can typically be taken anywhere from one to three times a day, depending on your doctor’s instructions. Both the individual dose and frequency of use determine your daily dosage.
The recommended maximum dosage is 37.5 milligrams (mg) per day.
The strength of a particular pill is determined by how many milligrams of phentermine HCL it contains.
Popular phentermine doses include:
In Australia and South Africa, it’s also possible to purchase Duromine, which comes in a maximum dose of 40mg .
Phentermine is sometimes prescribed in combination with a low dose of topiramate as a generic substitute for the brand name medication Qsymia.
Phentermine is an oral medication that comes in three forms:
Generic phentermine weight loss pills are available in capsule and tablet form. Brand name capsules and tablets are manufactured by several different pharmaceutical companies. The most common phentermine tablets are white, oblong pills with blue specks. Suprenza is an ODT form of phentermine.
Below are photos of popular tablets:
Phentermine capsules come in a variety of colors. Here are some of the most common caspules:
Suprenza is an ODT preparation of phentermine weight loss pills. Here’s what it looks like:
This medication is most-often taken once a day in the morning, either on an empty stomach or 1-2 hours after breakfast.
Depending on your doctor’s orders, you may be instructed to a pill anywhere from 1-3 times a day. However, the total intake of phentermine in one day should never exceed 37.5mg (or 40mg, if you are taking Duromine).
Phentermine should always be taken EXACTLY as it is prescribed by your doctor. It is also important to follow the directions and precautions on the medication’s label. Never change your schedule or dosage without your prescribing doctor’s approval.
If you are prescribed a capsule or tablet once a day, take it around breakfast time. Some brands recommend taking it on an empty stomach before eating, while others can be taken about 2 hours after eating. Suprenza (ODT) can be taken with or without meals.
It is, however, advisable to take phentermine early in the morning because:
If you are taking phentermine multiple times a day, follow your doctor’s and pharmacist’s directions precisely regarding the dose and schedule.
This medication should be taken for up to 12 weeks (3 months) at a time because it can become habit-forming if it is consumed for longer periods . More specifically, research shows that taking phentermine for up to 6 months may lead to psychological dependence, restlessness, insomnia, a rapid heart rate (tachycardia), and high blood pressure . However, abrupt cessation can also produce withdrawal symptoms. This is why it is important to strictly adhere to the prescribing instructions.
Due to the medication’s potency and chemical structure, withdrawal symptoms can occur when you stop taking phentermine.
Some potential withdrawal signs include:
If you recently stopped taking phentermine and are currently experiencing any of these symptoms, contact your prescribing doctor for advice and assistance.
To minimize the risk of these complications, speak with your doctor about gradually decreasing your dosage instead of stopping the medication abruptly.
Due to an increased risk of seizures, Qsymia should not be stopped abruptly unless this process is initiated under direct medical supervision. If a Qsymia prescription is discontinued, the patient should be gradually weaned off of the medication to reduce this risk.
Many people find themselves searching for continued appetite suppression after their prescription ends, and since phentermine should only be taken for a few weeks at a time, some patients seek-out a more long-term option.
Phen Caps is a dietary supplement that helps suppress the appetite and boosts energy naturally. It does NOT contain any phentermine HCL, but instead relies on nine natural ingredients to support users' weight loss efforts. Phen Caps are an effective and natural appetite suppressant with positive customer reviews and a 100% satisfaction guarantee. Phen Caps are only available online at phen.com.
No, phentermine is a prescription medication.
If you decide that you’re interested in OTC supplements that you can buy online & without a prescription, consider our favorite natural appetite suppressant – Phen Caps.
Phentermine is a prescription medication.
A licensed physician - your primary care physician (PCP/GP), a weight loss specialist or another practitioner - can write the script. After your appointment, you can fill this prescription at any major pharmacy.
Many stores even offer a mail-order pharmacy option so, if you prefer, you may be able to buy phentermine online (fill your prescription) though one of these services.
Click here to learn all about How to Buy Phentermine Online.
Alternatives include other prescription weight loss drugs or OTC weight loss supplements.
Prescription weight loss drugs are a huge market in the US, and only expected to grow. Some of the alternative prescription weight loss medications that are popular include:
Here’s more about each of those alternative prescription weight loss drugs:
Many companies produce weight loss supplements that are meant to suppress the appetite, reduce cravings, and boost energy levels. However, supplements are not as heavily regulated and are not approved by the FDA. As a result, you should be cautious when ordering dietary supplements. Remember: phentermine is not available without a prescription. This means that if you see a website claiming to sell this medication without a prescription, the company is either selling a supplement or counterfeit phentermine.
Among the many options available for weight loss supplements, we recommend Phen Caps. Phen Caps is an all-natural supplement that is formulated with nine natural ingredients that support weight control and increase your energy.
Adipex, formally known as Adipex-P, is the most popular brand of phentermine in the US.
This medication contains phentermine HCL as its main ingredient, it is manufactured by GATE pharmaceuticals, and it is available as either tablets or capsules – both of which provide a maximum dose of 37.5 mg. Adipex-P is typically taken once per day, either before breakfast or 1-2 hours after breakfast. However, in some cases it may be preferable to split the Adipex tablet in half and take two smaller doses instead.
This is what Adipex capsules and tablets look like:
Apipex-P blue and white capsules, 37.5 mg Adipex tablets
Adipex (or Adipex-P) is a specific brand of weight loss pills, while “phentermine” refers to all generic and brand name products with the single active ingredient of phentermine.
Lomaira is a low-dose brand of phentermine weight loss pills. This medication is manufactured by KVK Tech and it provides the lowest-available dose of just 8 mg per pill. It can be taken up to three times a day, and this makes Lomaira popular for patients who do not tolerate higher doses, or for people who struggle with nighttime cravings.
This is what Lomaira tablets look like:
Qsymia is a combination of topiramate extended-release (brand name: Topamax) and phentermine HCL.
Despite its relatively-recent FDA approval, Qsymia is very popular. It differs from other pills because it contains more than one active ingredient. While phentermine works to suppress the appetite and boost energy, topiramate supports further weight loss by promoting the loss of body water . Qsymia comes in four different doses (all capsules) that can be used progressively. One benefit of this brand is that it is approved for a longer period of use than phentermine alone . Qsymia is manufactured by VIVUS, Inc.
This is what the different doses of Qsymia look like:
No. Phentermine was initially approved for the Canadian market but was later withdrawn due to safety concerns. The last available brand (Ionamin) was removed from market in 2007 .
Yes. Similar to the United States, phentermine is a prescription medication in Mexico and can only be legally obtained with a doctor’s prescription. You can fill a valid phentermine prescription at most major pharmacies.
Common brands in Mexico include Acxion, Terfamex and Raamcap, in addition to generic preparations .
Yes. This medication is widely available in Chile.
Phentermine sales have actually exploded in Chile in recent years, going from less than 4,000 boxes in 2012 to almost 1,000,000 boxes in 2017 – just five years later ! To purchase this medicine in Chile, you’ll need a valid “receta cheque” from a medical doctor. You can then fill this prescription at most major pharmacies.
Common brands available in Chile include Compulxine, Elvenir, Finapet, Obexol and Sentis, in addition to generic preparations.
No. Prescription appetite suppressants are not available from the NHS.
Stimulant-based appetite suppressants were withdrawn from the market following the European Medicines Agency’s 2000 decision to ban such substances throughout the EU. Following this ruling, the only prescription weight loss medications available through the NHS are Xenical or Alli . These pills both contain orlistat as the active ingredient and work by decreasing the absorption of dietary fat in one’s GI tract.
No. In 2000, the European Medicines Agency ruled to ban prescription appetite suppressants sales across the region. The agency’s recommendation to remove phentermine from the market was based on concerns about patient safety and potential addiction or abuse . Several countries that had previously permitted the prescription/sale of phentermine withdrew the medication from market following this decision.
Yes. Phentermine is widely-sold in Australia, but always under a doctor’s prescription. Like other countries, Australia dictates that this medication should be used for three months or less to manage exogenous obesity. If you live in Australia and you’re interested in a prescription appetite suppressant, schedule an appointment with your GP.
If you receive a prescription for this stimulant, you can fill the order at many Australian pharmacies. A higher-dose of phentermine (40mg) is available for patients in Australia and sold under the brand name Duromine.
Brands of phentermine available in Australia include Duromine, Ionamin, Metermine and generic phentermine resin .
Results vary drastically from person to person, but many people lose an average of 1-4 pounds per week while taking this medication.
It is impossible to predict exactly how much weight you’ll lose with phentermine given significant individual differences. However, based on Success Stories, you can anticipate losing anywhere from 1-4 pounds each week. Many patients lose more weight during the first month while taking phentermine, and then they tend to experience a more gradual decrease in weight during the following months. The results are also highly dependent on a users’ personal commitment to making lifestyle changes such as eating a healthy diet, engaging in regular (doctor-approved) exercise, and using stress management strategies.
Unless your doctor has specifically told you otherwise, you should eat at least 1200 calories per day if you’re a woman or at least 1500 calories per day if you’re a man. These are the minimum caloric requirements that sustain basic functions and prevent your body from going into starvation mode.
While fast, dramatic weight loss may seem appealing in theory, it is actually healthier and more sustainable to lose a moderate 1-2 pounds each week. More importantly, with slower weight loss, you can help your body gradually adjust to the weight change and minimize the damage that could otherwise develop from a rapid and drastic reduction of weight.
If you’re looking for more specific tips about what to eat while taking phentermine, click here!
Phentermine is designed to be a temporary add-on treatment that improves weight loss results that are achieved through behavioral changes. Therefore, you should strive to incorporate long-term fitness and healthy eating habits into your daily routine.
Experts recommend a combination of cardiovascular (aerobic), strength, flexibility, and balance exercises to promote overall fitness. You should aim for 75 minutes per week of vigorous aerobic activity (e.g. running, swimming, etc.) or 150 minutes per week of moderate aerobic activity (e.g. walking, biking, etc.). This equals about 25 minutes, 3 times a week of exercises like running OR 30 minutes, 5 times a week of exercises like walking. This is one of the best ways to incorporate healthy habits into your lifestyle and to naturally increase your weight loss.
After a couple of weeks or months, many people find that the medication’s effects start to decrease. Understandably, a lot of people wonder how they may be able to enhance and sustain their results. The best way to achieve this goal is through a strict diet adjustment, a long-term commitment to exercising, and by finding ways to get adequate amounts of sleep.
However, if you feel like your medication is no longer working, speak to your prescribing doctor about your concerns. This may indicate that you’ve developed a tolerance to phentermine. In that case, you should take a break from the weight loss pills.
Boost your weight loss with the following tips:
Want to see real success stories from actual people?
Our Success Stories section features past & present phentermine users’ motivational pictures and stories! They talk about their motivations, challenges, victories, and accomplishments in order to inspire and prepare you for your weight loss journey!
Here are two inspiring success stories:
Chandra: 216 pounds to 142 pounds
Brandon: from 320 pounds to 170 pounds
For more phentermine success stories, check out our Success Stories section here!
If you’re curious about how past & present users felt about their experience with phentermine, watch this short video to find out!
Interested in how real patients rate their experience with this medication? Below you will find hundreds of users’ ratings and comments about generic pills, Qsymia, Adipex and more! To see dozens more reviews, please visit our phentermine reviews page.
Weight loss is as much of a mental challenge as it is a physical one. Through the ups and downs of weight loss – both emotionally and on the scale – it can prove to be a struggle to remain devoted. Fortunately, research shows that those who stay committed to their weight loss journey enjoy the highest rates of long-term success .
Your peers also play an especially important role in helping you stay motivated and accountable. A 2016 study found that individuals who embark on a weight loss journey with friends or family are significantly more likely to achieve and maintain their goal weight . This beneficial social support can be in-person from a friend, spouse or coworker, or from a new online friend. Many people choose to keep their phentermine use a secret. Therefore, online support groups and forums play a major role in providing support for many patients.
Below you will find descriptions and links for our supportive, informative and lively online communities and support groups. Check them out and join today!
Our official Facebook page is your source for all things phentermine! We share weekly updates to the blog, current users’ daily menus and routines, and weight loss tips. In addition, we connect you with our Phentermine Ambassadors.
Losing Weight with Phentermine is our official Facebook support group in English. More than 7,000 users log-in daily to ask questions, share tips and tricks, and support each other in their weight loss journeys!
Grupo Oficial de Apoyo de la Fentermina is our official Facebook support group in Spanish. Each day, more than 5,000 real phentermine users from all over the world log-in to ask questions, share practical advice and support each other in their weight loss journeys!
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21. Australian Government Department of Health. (2018). Search the TGA website. Retrieved from https://tga-search.clients.funnelback.com/s/search.html?query=phentermine&collection=tga-artg&start_rank=1