Stopped Working

Phentermine Stopped Working

Phentermine is a popular and effective weight loss medication, but unfortunately, many users report that phentermine stops working after 2-3 months of use.

This decreased effectiveness is common because of the body’s natural response to weight loss and increased phentermine tolerance.

Woman examining a packet of pills
Tolerance may be to blame if your phentermine stopped working

Phentermine Tolerance

Over time, the body adapts to phentermine and its effectiveness can decrease. Phentermine tolerance is an especially common problem for patients who have taken phentermine for a long time or are taking it for the second or third time. 

How long does phentermine tolerance last?

There are no official clinical studies of how long phentermine tolerance will last. Patient reports indicate it can last for months or years after stopping phentermine.

Is phentermine tolerance permanent?

No. A tolerance to phentermine is not permanent – it typically improves after taking an extended break from the medication. 

Does a phentermine tolerance resolve after a break?

Tolerance often improves but does not resolve, after taking an extended break from phentermine.

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. Even people that do not feel much effect at first usually begin to appreciate the pill’s effects within a couple of weeks.

Contact your doctor if you do not feel phentermine’s desired effects 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.

What is a phentermine plateau?

feet on bathroom scale that is displaying the word "help"
Natural weight loss plateaus make some patients feel like phentermine is not working anymore

A plateau is a temporary stall in weight loss.

Most patients experience at least one phentermine plateau, often 1-2 months into treatment.

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There are three common explanations for a phentermine plateau:

1. Tolerance

One reason weight loss slows (or stops) a couple of months into treatment is increased phentermine tolerance. Patients tend to lose slower as the pills’ effects weaken.

2. Water Weight

Another reason is glycogen and water weight. Glycogen is the body’s most easily-accessible energy source. It is burned first when ‘calories in’ is less than ‘calories out’. However, in addition to quick energy, burning glycogen also releases a lot of water. As a result, many dieters lose a lot of water weight in the first few weeks. When the body eventually switches to other sources of energy (e.g. stored fat), this rapid weight loss stops ( 1 ).

3. Energy Balance

Finally, not adjusting intake and activity can also precipitate a phentermine plateau. A smaller, lighter body needs less fuel to power its everyday activities. So, it is important to adjust intake and activity to accommodate these now-lower needs.

5 Ways to Make Phentermine Work Again 

pink weights and a measuring tape
If phentermine has stopped working, try adding more activity to your daily routine to boost weight loss

Phentermine is designed as a short-term weight loss medication, and a decrease in effectiveness is often part of treatment with this pill. Thankfully, lifestyle changes can make a significant difference. 

1. Increase Everyday Energy

Phentermine is famous for the strong, immediate energy it provides patients, but sometimes this boost isn’t enough.

Get more everyday energy by choosing to:

  • Exercise regularly 
  • Eat nourishing foods
  • Stay hydrated
  • Prioritize sleep

Read more: How to Get More Energy from Phentermine

2. Boost Metabolism Naturally

Exercise 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 ( 3 ,4).

Some foods, drinks, and spices also have a beneficial effect on metabolism.

Read more: How to Boost Metabolism Naturally

3. Set SMART Goals

Research shows that people accomplish goals more frequently when the goals are “SMART” ( 5 ):

  • Specific
  • Measurable
  • Achievable
  • Related (to an overall goal)
  • Time-bound

Transform your abstract objectives into concrete SMART goals to give your weight loss journey a boost.

Read more: Setting Weight Loss Goals for Success

4. Prioritize Rest & Relaxation

Many people underestimate the importance of sleep and stress management in a successful weight loss journey. However, it’s vitally important to prioritize rest and manage stress.

Aim for 7-9 hours of sleep per night to balance hormones, reduce risk of chronic disease and give your body the time it needs to repair 6 ). Simple stress management techniques (like meditation) can also have a positive effect on weight loss ( 7 ).

Read more: Sleep and Weight Loss with Phentermine

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PhenQ is recommended by 190,000 people like you who want to lose weight fast and effectively without the drawbacks of prescription medications.

  • No Tolerance Build-Up.
  • No Prescription Required.
  • Money-Back Guarantee.

5. Take Supplements with Phentermine

In 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:

  • Melatonin
  • Capsicum/Cayenne Pepper
  • Pre-Workout Supplements
  • Vitamin B12
  • Conjugated Linoleic Acid (CLA)
  • 5-HTP

Read more: Best 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. Mayo Clinic Staff. (2018, February 06). Weight loss stalled? Move past the plateau.

2. Centers for Disease Control and Prevention. (2018, February 13). Healthy Weight.

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

4. Kinucan, P., & Kravitz, L. (n.d.). Controversies in Metabolism.

5. 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

6. National Sleep Foundation. (2014, November 13). How to Fall Asleep Fast.

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