Phentermine Withdrawal

Phentermine should only be taken for twelve weeks at a time.

This recommendation is related to the active ingredient’s strong potential for addiction and abuse, as well as a lack of research on the long-term effects of this medication ( 1 ). Plus, limiting use to “a few weeks” minimizes patients’ risk of dependency, tolerance and withdrawal.

Unfortunately, some people still experience withdrawal symptoms when they stop taking phentermine – even after a relatively short course of treatment.

woman holding yoga pose
Daily activity should be part of your plan for how to stop taking phentermine

Planning how to stop phentermine is important to help minimize phentermine withdrawal symptoms.

Phentermine is designed to be used alongside lifestyle modifications that promote weight loss ( 2 ). As you reach the end of your 12-week treatment period, focus on reinforcing healthy eating, exercise and self-care habits.

A strong support system, whether in-person or online, can help you stay committed to your new, healthier lifestyle.

For some patients, it’s also beneficial to taper phentermine dosage in the final weeks of treatment. A taper allows the body to gradually adjust to a lower level of stimulant, which helps reduce the risk of phentermine withdrawal.

If possible, do not stop phentermine “cold turkey,” or very suddenly ( 2 ).

Read more here: Stopping Phentermine

Phentermine Withdrawal Symptoms

woman with a headache and fatigue from phentermine withdrawal
One of the most common phentermine withdrawal symptoms is fatigue

Phentermine withdrawal symptoms are similar to those associated with other stimulants.

Common reactions include fatigue, depression/mood changes, insomnia, gastrointestinal upset and trembling ( 3 , 4 ). Severity varies significantly from person-to-person.

Call your doctor or seek immediate medical attention if withdrawal symptoms are severe, worsening or interfering with daily life.

Take extra care to monitor for signs of depression and low mood, which are the typically the most dangerous side effects of stimulant withdrawal, even months after the last dose ( 5 ).

How Long Does Phentermine Withdrawal Last?

analog wall clock
Duration of phentermine withdrawal varies from person to person

Duration of phentermine withdrawal varies from person-to-person. However, most people withdrawing from stimulants experience the most acute symptoms during the first four days, after which point they begin to feel better.

Lingering symptoms of stimulant withdrawal, such as low mood or fatigue, can last for weeks or months after stopping phentermine ( 5 ).

Life After Phentermine

green salad, weights and a jump rope
Adopting healthy habits during treatment may help you ease into life after phentermine

It’s critical that patients transition off phentermine with a plan for continued healthy living.

In fact, without a strong weight maintenance plan in-place, almost 80% of people who achieve major weight loss gain the pounds back within two years ( 6 ).

However, research shows that certain behaviors are highly-correlated with successful weight maintenance ( 7 ). These healthy habits include:

  • Eating breakfast
  • Weighing regularly
  • Cooking at home
  • Staying active
Read more here: Life After Phentermine
  1. Weintraub M, Hasday JD, Mushlin AI, Lockwood DH. (1984). A double-blind clinical trial in weight control. Use of fenfluramine and phentermine alone and in combination. Archives of Internal Medicine, 144(6):1143-1148.
  2. American College of Cardiology. (2011, November 21). Phentermine.
  3. Allina Health. (2013, June 12). Appetite suppressant, sympathomimetic.
  4. Drugs.com. (1999, April 26). Phentermine Hydrochloride Drug Information, Professional.
  5. Center for Substance Abuse Treatment. (1999). Chapter 5 – Medical Aspects of Stimulant Use Disorders. In Treatment Improvement Protocol (TIP) (Ser. 33).
  6. McGuire, MT, Wing, RR, & Hill, JO. (1999). The prevalence of weight loss maintenance among American adults. International Journal of Obesity and Related Metabolic Disorders, 23(12), 1314-1319.
  7. Wing, R. R., & Phelan, S. (2005). Long-term weight loss maintenance. The American Journal of Clinical Nutrition, 82(1), 222S-225S.
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