Has Your Phentermine Stopped Working?

Phentermine is a popular and effective weight loss medication, but unfortunately many users report that phentermine stopped working after 2-3 months of use. This decrease in effectiveness is common due to increased phentermine tolerance and biological regulation of weight loss, but that does not make it any less frustrating when you are working hard to lose weight and phentermine is not working anymore. Thankfully, simple lifestyle changes can boost the medication's effectiveness and help you overcome your phentermine plateau.

Phentermine Tolerance

Phentermine toleranceMost phentermine users experience a reduction in effectiveness over time. This reaction is typically due to increased tolerance. Over time, the body adapts to phentermine and the medication’s effects grow less pronounced. Phentermine tolerance and the associated decrease in utility is an especially common problem among patients who have taken phentermine for an extended period of time, or already took phentermine before and recently returned to the medication. 

How long does phentermine tolerance last?

Phentermine tolerance varies from patient to patient. There is no reliable estimate of how long phentermine tolerance will last, but patient reports indicate it can linger for months or years after stopping phentermine.

Is phentermine tolerance permanent?

A tolerance to phentermine is not permanent in the sense that it typically improves after a taking an extended break from the medication. However, each person has their own experience and many repeat users feel that subsequent rounds of phentermine never work as well as the initial treatment. 

Does a phentermine tolerance resolve after a break?

Tolerance often improves, but does not resolve, following an extended break from phentermine. In fact, some states enforce a maximum prescribing period and mandatory break period to reduce the risk of addiction and phentermine tolerance. For example, in Ohio phentermine (and other prescription weight loss medications) can only be prescribed for 12 weeks at a time, after which time the patient must take at least a 6 month break before attempting further pharmaceutical weight loss [1]. Laws like these suggest that there is at least some evidence for reduced phentermine tolerance, and increased effectiveness, following a multiple month break.

Phentermine tolerance is common after a couple of weeks or months of use, but what if phentermine is not working the first week of treatment? It is surprisingly common to read user reports that phentermine did not “kick in” for 2-3 days. Thankfully, most people that continue taking their medication as prescribed begin to feel the pill’s effects within the following couple of weeks.

Contact your doctor if you do not feel any of phentermine’s desired effects (e.g. appetite suppression, increased energy, etc.) within the first week. He or she also needs to know if you are experiencing any side effects that persist, worsen or interfere with your daily life.

Phentermine Plateau 

Phentermine plateauMost patients will experience one or more phentermine plateaus, often in month two of treatment. Increased tolerance, depletion of glycogen and not adjusting intake can all contribute to a plateau on phentermine. 

When you cut calories or increase physical activity, the body draws on its own reserves to provide the necessary fuel. The first choice of stored energy is glycogen: a carbohydrate stored in the liver and muscles. The body burns through glycogen before tapping into stored energy from fat because the former is more metabolically-available to provide quick energy.

Glycogen releases a lot of water when it is burned for energy, so many dieters lose a significant amount of water weight in the first few weeks. Eventually, however, your body switches to other sources of energy (e.g. stored fat) for fuel and this rapid weight loss ceases. This switch, which is actually beneficial and necessary for long-term weight loss, is at least partially-responsible for the dreaded phentermine plateau [2].

Not adjusting intake and activity for your now-smaller body can also contribute a phentermine plateau. When there is less of you, your body needs less fuel to power its everyday activities. So, it is important to adjust your intake and activity to accommodate these now-lower needs.

Lastly, it is only healthy to lose about 1-2 pounds per week long-term, so losses naturally become slower and steadier after the first few weeks [3]. This more moderate weight loss ensures that your body has the fuel it needs to lose fat and gain lean muscle mass simultaneously – a critical factor in achieving and maintaining major weight loss.

How long do you plateau on phentermine?

Like any other weight loss plateau, phentermine plateaus are normal and completely individual. There is no way to scientifically predict how long a plateau will last. If you are concerned about your recent lack of weight loss with phentermine, try to focus on non-scale victories and experiment with some of the tips below to get the scale moving again!

How to Make Phentermine Work Again 

Phentermine is designed as a short-term weight loss medication, and a decrease in effectiveness is often part of treatment with this pill. This prompts many users to wonder, "How can I get phentermine to work again?". Lifestyle changes can make a significant difference to boost phentermine, but it is also important to remember that just because weight loss slows does not mean that phentermine is not working. Medically, a moderate drop of 1-2 pounds per week is considered healthy weight loss [3]. 

How to keep phentermine working:

  1. Increase energy with healthy diet and exercise
  2. Boost metabolism naturally
  3. Set SMART weight loss goals
  4. Sleep for weight loss
  5. Consider taking supplements with phentermine

1. Increase energy with diet and exercise

Increase energy with diet and exercisePhentermine is famous for the strong, immediate energy it provides patients, but sometimes this boost isn't enough. Whether you no longer have energy from the pills due to increased phentermine tolerance, or never felt the extra energy in the first place, you will be happy to hear there are several ways to get more energy from phentermine. During your weight loss journey, choose to exercise regularly, consume nourishing foods, stay hydrated and prioritize sleep. While it may sound counter-intuitive, hitting the gym (or taking a walk) 3-6 times per week has been shown to increase energy and decrease fatigue [4]. More, eating right, planning your meals and staying well-hydrated gives your body the fuel it needs and helps keep energy levels up throughout the day. Click on the link below to learn about foods and behaviors that boost energy and promote weight loss naturally.

 Read more here: How to Get More Energy from Phentermine

2. Boost metabolism naturally

Boost metabolism naturallyExercise is critical for maintaining a healthy and speedy metabolism. Combining moderate aerobic activity (150 minutes per week) with regular strength-training exercises (2-3x per week) has been shown to improve both stamina and maintain lean muscle mass [5]. This is important because weight loss, especially rapid weight loss, threatens metabolically-active lean muscle mass. Aim to include muscle-building activities like strength-training to maintain and boost metabolism [6].

Some foods, drinks and spices also have a beneficial effect on metabolism. Click on the link below to discover healthy habits and nourishing foods that boost metabolism even more!

 Read more here: How to Boost Metabolism Naturally

3. Set SMART weight loss goals

SMART weight loss goalsResearch shows that people accomplish goals more frequently – both in weight loss and in life – when the goals are SMART [7]:

As you set-out on your weight loss journey with phentermine, work to transform your objectives into SMART goals. While this might take more time or planning in the beginning, it will be worth it in the end when you achieve your goal and stick with the changes long-term. 

 Read more here: Setting Weight Loss Goals for Success

4. Sleep for weight loss

Sleep for weight lossMany people underestimate the importance of sleep and stress management in a successful weight loss journey. As you work to improve your diet and become more active, try to also work on prioritizing rest and managing stress.

Aim for 7-9 hours of sleep per night to balance hormones, reduce risk of chronic disease and give your body the time if needs to repair [8]. More, research shows that even simple stress management techniques can have a positive effect on weight loss [9].

 Read more here: Sleep and Weight Loss with Phentermine

5. Take supplements with phentermine

Take supplements with phentermineIn an effort to make phentermine work better, many patients look for supplements to take with phentermine. ALWAYS check with your prescribing doctor and pharmacist before taking any medication or supplement with phentermine – even if the product is “all natural”.

Some  of the most common supplements to take with phentermine include:

5-HTP, for example, is a popular choice because research suggests that it may boost weight loss, plus decrease symptoms of insomnia and low mood [10-13]. Vitamin B12 shots are often prescribed by weight loss clinics to boost phentermine, but not all doctors agree that this supplementation is useful [14]. 

If you are searching for a supplement to provide continued appetite suppression and added energy, we recommend Phen Caps. These all-natural, over-the-counter capsules are a great option to keep your weight loss going as you transition off prescription phentermine.

 Read more here: Supplements to Take with Phentermine

 The most effective way to take phentermine is exactly as prescribed. If you are unsure when or how to take phentermine, check with your doctor and pharmacist as soon as possible. NEVER take phentermine more often or at higher doses than prescribed.



1. Ohio Administrative Code. (2016, February 29). 4731-11-04 Controlled substances: Utilization of short term anorexiants for weight reduction. Retrieved from

2. Mayo Clinic Staff. (2018, February 06). Weight loss stalled? Move past the plateau. Retrieved from

3. Centers for Disease Control and Prevention. (2018, February 13). Healthy Weight. Retrieved from

4. Puetz, T. W., Flowers, S. S., & O’connor, P. J. (2008). A Randomized Controlled Trial of the Effect of Aerobic Exercise Training on Feelings of Energy and Fatigue in Sedentary Young Adults with Persistent Fatigue. Psychotherapy and Psychosomatics, 77(3), 167-174. doi:10.1159/000116610

5. American Heart Association. (2015). Answers by Heart Fact Sheets: Lifestyle and Risk Reduction. Retrieved from

6. Kinucan, P., & Kravitz, L. (n.d.). Controversies in Metabolism. Retrieved from folder/metabolismcontroversy.html

7. Shaw, R. L., Pattison, H. M., Holland, C., & Cooke, R. (2015). Be SMART: Examining the experience of implementing the NHS Health Check in UK primary care. BMC Family Practice, 16(1), 1. doi:10.1186/s12875-014-0212-7

8. National Sleep Foundation. (2014, November 13). How to Fall Asleep Fast. Retrieved from 

9. Pratt, K. (2014, January 8). UK researcher finds stress management may contribute to weight loss. Retrieved from

10. 5-hydroxytryptophan, eating behavior and adherence to dietary prescriptions in obese adult subjects. (1989). Clinical Nutrition, 8, 49. doi:10.1016/0261-5614(89)90158-1

11. Amer, A., Breu, J., Mcdermott, J., Wurtman, R. J., & Maher, T. J. (2004). 5-Hydroxy-l-tryptophan suppresses food intake in food-deprived and stressed rats. Pharmacology Biochemistry and Behavior, 77(1), 137-143. doi:10.1016/j.pbb.2003.10.011

12. Shell, W., Bullias, D., Charuvastra, E., May, L. A., & Silver, D. S. (2010). A Randomized, Placebo-Controlled Trial of an Amino Acid Preparation on Timing and Quality of Sleep. American Journal of Therapeutics, 17(2), 133-139. doi:10.1097/mjt.0b013e31819e9eab

13. Shaw, K. A., Turner, J., & Mar, C. D. (2002). Tryptophan and 5-Hydroxytryptophan for depression. Cochrane Database of Systematic Reviews. doi:10.1002/14651858.cd003198

14. Bauer, D. B. (2018). Are vitamin B-12 injections helpful for weight loss?  Retrieved from Mayo Clinic: