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Phentermine Dosages for Weight Loss

Successfully used as an appetite suppressant since 1959, phentermine has been widely used short term to aid weight loss. Although it is available to buy in most countries, its safety has always been up for discussion over the years.

If you’re here looking for the right phentermine dosages for your weight loss goals, it’s time to pay attention! Before you get started, it’s important to gather all of the facts. We’ve covered everything you need to know, including: how phentermine works, its history, any possible side effects, phentermine dosages for weight loss and everything in between.

So, what is phentermine?

Similar to amphetamine – phentermine is commonly prescribed to help treat obesity. As a result of its appetite-suppressing powers, phentermine has quickly become the most popular weight loss drug in the US. It is often marketed under brand names, such as Suprenza or Adipex-P. However, you’re not going to find phentermine over-the-counter, as it is only available with a prescription. If you are looking for an alternative you can simply buy, alternative and phentermine combinations can be bought quite easily.

To understand why phentermine has become the go-to pill for shedding stubborn weight, we take a closer look into America’s favorite weight loss drug.

How does phentermine work?

Phentermine stimulates the release of brain chemicals that manipulate your mind to suppress your appetite – giving you a feeling of fullness, therefore eating less. It works as an anorectic (or anorexic), in three stages.

  1. Phentermine stimulates the neurons in your brain, encouraging the release of a type of neurotransmitter called catecholamines – including norepinephrine and dopamine.
  2. Catecholamines in high levels work to curb hunger signals, therefore suppressing your appetite (and that pesky need to snack!).
  3. As a result of the above, when your body tells you it’s hungry, your brain doesn’t receive the message.

Both dopamine and norepinephrine are involved in your brain’s stress responses. This means that when neurotransmitters are released, the fight-or-flight response is signalled. This response can cause your blood pressure and heart rate to increase, leading to a reduction in appetite.

During clinical trials, the effects of phentermine have shown that when compared to other weight loss drugs and placebos, phentermine has resulted in more substantial weight loss. A review in The JAMA Network analysed 28 of these clinical trials, which studied nearly 30,000 overweight adults. The result? They found that 75% of participants taking phentermine achieved at least a 5% weight loss, in comparison to the 23% not taking the drug.

How do phentermine pills get prescribed?

Due to its effect as an anorectic, phentermine pills are prescribed to help people jumpstart their weight loss. However, it’s not quite available to everyone. Phentermine is generally only prescribed to those with a body mass index (BMI) of 30+. If a patient has other health factors, such as hyperlipidemia, hypertension or diabetes, they may be prescribed phentermine with a lower BMI of 27-19.

Despite what many believe, phentermine isn’t quite going to do all the hard work for you. To get the greatest results from taking phentermine drugs, it is always recommended that patients adopt a healthier lifestyle and drop their calorie intake. While it might help you lose a little weight when used independently, it is better paired with a healthy diet.

With a range of possible side effects alongside phentermine, it comes as no surprise that doctors are apprehensive about prescribing them. Like any new medication, a medical professional will weigh up the potential benefits with any potential risks before prescribing. They may also encourage you to lose weight naturally before seeking a diet pill. This reluctance by doctors has led to an increase in natural, prescription-free alternatives, such as PhenGold.

Phentermine and its history

First approved by the Food and Drug Administration (FDA) for its use as a weight loss drug in 1959, phentermine is no new kid on the block. It soon became available in a hydrochloride salt and resin form, referred to as phentermine hydrochloride. It was later blended with both dexfenfluramine and fenfluramine – with both acting as appetite suppressants – and marketed as Fen-Phen. This combination drug aimed to burn fat, fight obesity and suppress the appetite.

In 1977, fenfluramine and dexfenfluramine were removed from the market by the FDA as a result of 24 cases of heart valve disease in Fen-Phen users.

In its own right, phentermine as a substance was allowed to remain and is readily available in most countries. However, in many countries, it is still classed as a controlled substance – including in America – due to its similarities to amphetamine. As a result of this, phentermine as an independent drug is only available via prescription.

Are there any side effects involved?

Most drugs these days have some sort of side effect. Phentermine is no different. Although not all of its side effects are serious and some many decrease with time, they need to be paid attention to. If any side effects do occur, it’s always best to consult with a medical professional if they continue or get worse.

Some of the most common side effects of phentermine include:

  • Hyperactivity.
  • Headaches.
  • Insomnia.
  • Constipation.
  • Vomiting.
  • Diarrhoea.
  • Increased (or decreased) sex drive.
  • Bad taste in the mouth.

If you start to experience any of these common symptoms and they persist or worsen, speak to your doctor for advice.

Although the above are pretty common side effects of phentermine, there are more serious side effects to look out for too. If these occur, seek medical attention immediately. These include:

  • Chest pains.
  • Difficulty breathing.
  • Severe headaches.
  • Dizziness.
  • Pounding or irregular heartbeat.
  • Seizures.

Phentermine can impact your body in other ways, too – as it can also affect your mental health. Due to the way it works, phentermine is often referred to as a psychostimulant, causing a temporary increase in physical or mental functions.

If you’re still unsure what that quite means, let’s take a look at other psychostimulants:

  • Cocaine.
  • Methamphetamine.
  • Nicotine.
  • Ecstasy.

Similar to other psychostimulants, phentermine pills can result in both minor and severe mental health side effects, including:

  • Depression.
  • Anxiety.
  • Anger.
  • Agitation.

Keep an eye on your mood whilst taking and weaning yourself off of phentermine as depression can be a common side effect of phentermine withdrawal.

As mentioned previously, if you notice any substantial physical or mental changes while taking phentermine, get in touch with a medical professional as soon as possible. While the more minor side effects are quite common, they can still be uncomfortable to put up with. Contact your doctor if they persist, as they may be able to prescribe an alternative medicine or help you ease any discomfort.

When shouldn’t you take phentermine?

Although phentermine may have proved itself as a weight loss drug, that doesn’t mean it is suitable for everyone.

If any of the following apply to you, don’t take phentermine:

  • You’re pregnant or breastfeeding.
  • You have heart disease.
  • You suffer from very high blood pressure.
  • You have an overactive thyroid.
  • You have glaucoma.
  • You have a history of pulmonary hypertension.

Phentermine won’t be suitable if you have had a monoamine oxidase inhibitor (MAO) in the last two weeks. Used to treat depression and anxiety, they are generally prescribed when other antidepressants have been ineffective. A combination of phentermine with MAO inhibitors – such as rasagiline, linezolid or isocarboxazid – can cause an incredibly dangerous drug interaction and is best avoided.

Phentermine abuse

If you have a history of drug abuse, don’t take phentermine. While any prescription drug can be addictive to users, due to phentermine’s stimulant nature it can be especially addictive because of its effects on your body and mind. Those who take phentermine can get addicted to the feeling of increased focus and energy, as well as its effects as an anorectic. As it has become the go-to for losing weight, those trying to reach their ideal body weight as quickly as possible often take more than the recommended dosage of phentermine, finding themselves reliant on the drug.

To avoid this happening, always take the recommended dosage of phentermine as directed, and speak to a medical professional if side effects persist or you feel as though you are becoming addicted.

Phentermine dosages

So, what is the recommended phentermine dosage for weight loss? And what doses does phentermine come in?

The recommended adult dose is 8mg take orally three times a day, 30 minutes before a meal. Alternatively, a 15 to 37.5mg dosage can be taken one a day, either before breakfast or a couple of hours after.

Regardless of which phentermine dosage you’re prescribed for your weight loss, it is best to avoid taking phentermine later in the day. As we already mentioned, a common side effect is insomnia, so be sure to take your dose as early in the day as you can to avoid staring at your ceiling all night.

How much do phentermine pills cost?

The price of phentermine can vary, according to your prescribed dosage and the pharmacy you visit. For oral capsules, the price starts at $17.09 for a pack of seven 15mg capsules. A pack of 37.5mg capsules is available from $20.53.

Phentermine oral tablets are a little cheaper than the capsules, with a pack of seven tablets starting at $10.40.

Phentermine alternatives

Phentermine, amongst many others, work by curbing your hunger. Although phentermine has remained the most popular prescription-only weight loss drug in America, there are other prescription medicines available that claim to do the same thing. We’ve taken a look at some other anorectics, comparing their differences and similarities to America’s favorite.


Marketed under the names Didrex, Recede and Rigimex, benzphetamine is also an amphetamine with anorectic effects. With a similar impact on the body, their side effects are also much of the same – with neither to be taken if you’re pregnant or breastfeeding.


Phendimetrazine works differently to phentermine. Phentermine works by affecting your hormone levels, while phendimetrazine stimulates the central nervous system – increase your heart rate and suppressing your appetite. Expect to find phendimetrazine under the brand names Bontril PDM, Plegine and Adipost.


Sold under brand names Tepanil, Tenuate Dospoan and Tenuate, diethylpropion is also a stimulant drug. However, during clinical studies, it was found to be less effective than phentermine as a weight loss drug.


Sold under the brand name Desoxyn, methamphetamine is often considered the last resort of weight loss drugs due to its powerful and addictive nature. As a powerful central nervous system stimulant, it isn’t the first to be prescribed to treat obesity.


Unlike phentermine, orlistat isn’t an anorectic and doesn’t work to suppress your appetite. Instead, its powers sit with the way it blocks some of the fat you consume, keeping it from being absorbed by the body. Again, unlike phentermine, it is suitable for long term use. You can expect to find it sold under the brand names Xenical and Alli.


Commonly combined with other medicines, including phentermine, topiramate is actually an anticonvulsant (also known as antiseizure or antiepileptic drugs). When combined with phentermine, you can expect to find topiramate under the brand name Qxymia. In the same way phentermine’s dosage is suggested, it is best taken alongside a healthy diet and regular exercise.

Lose weight safely with PhenGold

Just like phentermine, PhenGold works best when partnered with a healthy lifestyle. Not only is it highly effective, but it’s also safer, natural and more affordable. Plus there’s no need for a prescription.

PhenGold works by reducing your food cravings and increasing your metabolism to burn off stubborn fat. Packed with clinically proven ingredients, losing weight doesn’t need to put your health at risk.



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Written by PhenGold

Written by PhenGold

We research and write articles about health, fitness and dieting. Each of our articles includes sources from scientific studies where possible.

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