Why is Phentermine not Working for me? (explained)

January 8, 2024 |

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This article will solve the mystery behind why phentermine is not working for you.

So has it been a few weeks since your phentermine treatment started, and you are feeling that your hunger pangs are resurfacing and that it is not giving you that usual energy boost anymore?

There could be many reasons why your weight loss has reached a halt. And drug tolerance is one of the main occurrences that explains this phenomenon. Other reasons could be substandard pills or noncompliance with either the prescription, diet, or exercise regimen.

This article will discuss the reasons behind your phentermine’s ineffectiveness and how you may enhance its benefit.

So, keep reading to find out the details.

Possible reasons why Phentermine is not working for you

You are not magically going to fit in your small-waisted pants just because you started taking phentermine. You should rather think of phentermine as a tool that will make it easier for you to shift to a lifestyle that will promote weight loss.

Counterfeit pills, drug tolerance, incompliance, and gaps in your diet are some of the many possible reasons why phentermine is not working for you, so head down to find out their details.

1. Fake phentermine pill

You may have bought a fake pill, and this might be one reason why phentermine is not working for you.

Phentermine is a prescription drug and a class IV-controlled substance, which means that you can’t purchase it without your doctor’s recommendation.

But since it is one of the most effective FDA-approved weight loss pills, there is a high consumer demand associated with it. And this demand is exploited by illegal suppliers who swindle money out of consumers by supplying them with unregulated and substandard pills.

If your phentermine is not working, check if you bought your drug online or from unverified vendors.

Other ways to spot substandard pills are to check for manufacturer or imprint codes, grammatical mistakes on the packaging list, or misleading advertising. You may find other differences between real and counterfeit pills on phentermine.com.

2. Incompliance

Phentermine is prescribed with some exercise and a diet plan, and not complying with either one of these determinants may disrupt the whole weight loss equation.

For instance, phentermine helps suppress hunger and increase your energy levels and focus. If you skip your daily dosages, it can lead to opposite effects, which may justify why phentermine is not working for you.

The same energy and focus that phentermine helps to increase are supposed to be utilized in exercise so that you lose body mass but being lazy to hit the gym will halt your weight loss progress.

Observing a calorie deficit and not starving is also crucial for losing weight with phentermine. Because if you start skipping meals or follow crash diets, it will only sabotage phentermine’s purpose by increasing cravings, hunger, and fatigue and will also make weight maintenance difficult.

3. Caffeine and Alcohol

Your intake of either caffeine or alcohol or both may be rendering phentermine ineffective.

Caffeine has an acidic pH, and it lowers the pH of urine which causes more unchanged phentermine to be excreted faster from the body. On the other hand, alcohol affects the liver, which plays a crucial role in phentermine metabolism and the fat-burning process.

4. Drug tolerance

Our bodies intelligently notice a recurring stimulation of the central nervous system and will stop responding to it after some time.

What happens is that the phentermine will trigger the release of neurotransmitters in the synapse (junction between two neurons), but the neurons would downregulate their receptors and stop receiving it. Which ultimately causes no effect on the suppression of appetite.

Most users usually observe a phentermine plateau 2 to 3 months into treatment, which occurs because the body is becoming tolerant to the prescribed phentermine dosage.

Plateau is basically a stall in your progress of losing weight which might make you feel like phentermine is not working.

This study evaluated the efficacy and tolerance of phentermine in 144 obese patients for 6-months and reported that almost 66% of the total participants developed a tolerance to the drug.

25% of them developed tolerance in the second month, whereas 41% developed tolerance in the fourth month.

How to increase effects of Phentermine for weight loss

There are other ways to increase the effects of phentermine instead of increasing its dosage. And you can achieve it just by fixing your lifestyle.

So, head down to find out what lifestyle modifications you may incorporate in your weight loss regimen to enhance the effects of phentermine.

1. Stay well hydrated

Drinking an adequate amount of water will produce alkaline urine that reduces the percentage of the eliminated unaltered drug and slows down its elimination process.

Consequently, the phentermine stays longer in your body and exhibits an enhanced potential to suppress appetite. Increasing your water intake with phentermine may also help prevent one of its common side effects of dry mouth.

According to NIH PubChem, only 48% of the unaltered drug is eliminated in alkaline urine compared to 84% in acidic urine.

This review also hypothesizes that better hydration leads to increased weight loss. It has included studies that show that better hydration reduces excessive feeding.

It speeds up the metabolism rate and the process of lipolysis, thus, promoting fat loss. The review has also included studies that elucidate an association between increased extracellular dehydration and a higher level of angiotensin II (AngII) hormone, which has a role in causing obesity.

Thus, to put it in simpler terms, better hydration may reduce the risk factors that cause obesity which adds up to the effects caused by phentermine and imparts more efficient weight loss effects.

So, remember to gulp down at least 8 glasses of water every day to enhance the weight loss effects of your phentermine.

2. Follow your exercise regimen

Exercising with a calorie deficit diet and phentermine will boost your weight loss and delay the onset of drug tolerance and weight loss plateau.

The reason is that exercise speeds up your metabolism, which increases the fat and calorie-burning process.

Phentermine gives you the energy to exercise even when you are on a calorie deficit, so you should utilize it wisely.

According to physical activity guidelines for Americans, if you are obese or overweight, you need to do about 150 minutes or more than 300 minutes of moderate or vigorous intensity exercise to lose about 5% of your body weight or maintain it.

An example of moderate-intensity activity is brisk walking, while aerobic exercises are of vigorous intensity.

3. Follow your diet plan

Phentermine does not promote weight loss on its own, and you need to create a calorie deficit of about 500 calories to drive your weight loss journey effectively.

However, taking phentermine might aid you in remaining consistent by helping you deal with the energy deficit and getting you through the hunger pangs.

According to this article published in the American journal of medicine, obese and overweight patients should consume around 800 to 1500 calories per day and reduce their fat intake, especially saturated fats, to 30% or less.

Taking only phentermine is futile to your weight loss progress if you are stuffing in more carbohydrates in place of fats and not following the calorie deficit.

Phentermine may work best if you cut down processed foods and sugar from your diet and incorporate 40% carbs, 30% fats, and 30% protein in your diet plan or as prescribed by your nutritionist.

Here is a phentermine diet by ‘Medmunch’ that you can consult for reference.

What can I take with Phentermine to make it work better?

For this section, I added some recommendations that may help increase phentermine’s effectiveness in inducing weight loss and make it work better.

  • Alkalizing foods

As mentioned above, alkaline urine (pH 7.5 to 8) ensures that the drug stays longer in the body, so eating alkalizing foods with phentermine will enhance its functions.

Fruits and leafy green vegetables are the best examples of alkalizing foods.

On your next grocery trip, you can pick up some spinach, avocado, turnips, horseradish, carrot, or cucumber to take with your prescription.

  • Combination therapy

Most doctors prescribe 5-HTP with phentermine as both have a role in appetite suppression.

Like phentermine, which increases the dopamine, epinephrine, and norepinephrine levels to suppress appetite, 5-HTP increases the concentration of the serotonin precursor 5-HT to bring about the same effects.

This murine study found that a triple-drug combination of phentermine, 5-HTP, and carbidopa leads to greater weight loss than individual drugs. The study also found that it reduces and reverses the psychomotor side effects caused by phentermine.

You may consult your doctor to prescribe a combination therapy or other supplements if you want phentermine to work better in your body.

Some examples of supplement drugs are Conjugated Linoleic Acid (CLA), vitamin B12, melatonin, etc.

  • Lemon water

The anecdotal evidence available online supports using lemon water with phentermine to reduce the risk of developing tolerance to it.

The reason could be that lemon is an alkalizing food, and water will promote hydration in the body which makes you achieve two purposes that may make your phentermine work better with just one drink.

The recipe provided on Phenterminedoctors recommends using 2 to 3 ounces of lemon in 1 quart of water.

How should I take Phentermine for best results?

Phentermine is a prescription drug, so you may get the best results from its use by strictly following the dosage and dosing instructions recommended by your doctor.

Phentermine is available in capsules, tablets, disintegrating tablets, and extended-release capsules.

You can find the different dosing instructions for all these forms on the packaging labels.

But to provide you with a brief guideline, take the capsules and tablets as a whole, don’t crush or chew them. And dissolve the disintegrating tablet on your tongue before drinking water.

Phentermine is mostly prescribed in an 18.75-37.5 tablet dosage or in the form of 10 to 15 milligrams capsules.

Your doctor may recommend you take it once a day, either before breakfast or two hours after it. But you should avoid taking it late in the evening due to its potential to cause insomnia. It is usually taken 12 hours before bedtime or at least 4 to 6 hours before sleeping.


To wrap it up, phentermine is only to be consumed short term mostly for 6 to 12 weeks, because it may start to lose its effect if the body develops tolerance.

Not modifying your lifestyle with phentermine may also be one of the reasons why phentermine may stop working for you.

If you feel like you have stopped losing weight with phentermine, you should discuss it with your doctor, and he may prescribe certain supplements or combination therapy or change dosages to make the treatment work again.

You may also try cutting down on alcohol and caffeine, ensure abundant hydration, and check if it restores phentermine function.

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