Get to Know Phentermine Withdrawal Symptoms

by Dr. Ahmed Zayed
Published on June 12, 2024
person holding tablets

Phentermine grabs the crown as the ultimate fighter against obesity. It’s not like those diet aids you can pick up online or at the pharmacy; phentermine has a heftier impact and requires a prescription. Because stopping certain medications can cause withdrawal troubles, it’s natural to question if phentermine could cause similar problems.

Throughout this article, you’ll learn more about phentermine withdrawal symptoms, why they occur, and how to avoid them.

Phentermine Withdrawal

Drug withdrawal is defined as a group of symptoms which occur due to the decrease in intake of medications and recreational drugs or their abrupt cessation. Withdrawal symptoms are associated with various pills so it’s natural to worry about whether phentermine can induce the same effect. Some evidence shows that people who take phentermine aren’t in danger of experiencing withdrawal symptoms.

The American Journal of Therapeutics published a study whose primary objective was to evaluate the abuse and addiction potential of long-term phentermine pharmacotherapy and effects of abrupt cessation of the drug in a weight management program. For this purpose, scientists enrolled 35 patients who abruptly stopped taking prescribed phentermine on their own initiative.

Subjects were examined using the 18-item Kampman Cocaine Selective Severity Assessment scale which was modified to analyze withdrawal from this drug. Scientists found that the abrupt cessation of phentermine use doesn’t induce cravings for the drug. Symptoms that were observed after the sudden intake of the drug were a result of therapeutic effect rather than a withdrawal itself (1).

Despite the fact, the study above showed phentermine isn’t associated with withdrawal symptoms, it’s not uncommon for people to complain they do experience various effects after drug cessation.

How Do Withdrawal Symptoms Occur?

While withdrawal symptom is such a frequently used term nowadays many people aren’t quite familiar with how they occur. Basically, withdrawal symptoms occur when a person develops drug dependence and stops consuming it suddenly. Dependence on some drug, in this case, phentermine, can be physical or psychological. Due to the stimulating effects of phentermine, some people may find the “high” effect pleasurable and develop a habit to use it just to feel that way.

On the other hand, some people may develop a form of dependence due to physical impact the drug has on their body. For instance, they may notice the drug is helping them slim down so they believe it would be impossible to lose weight without it. Regardless of the reason, abrupt cessation of phentermine use, in this case, can lead to withdrawal symptoms.

When you stop taking the drug abruptly your brain needs to adjust and adapt to the new situation as well as to the sudden change in the level of brain chemicals produced. Neurotransmitters such as dopamine and serotonin have a significant impact on your mood and overall health. As you stop taking drugs which work by stimulating your brain, the concentration of neurotransmitters alters, and it temporarily affects the way you perceive the world around you but also induces other symptoms.

That’s why phentermine withdrawal symptoms occur.

The whole purpose of phentermine is to act as a short-term assistant that helps obese individuals jumpstart their weight loss. Doctors only prescribe it for a limited amount of time only, usually 12 weeks (2). The problem occurs when people use it longer than recommended as they develop drug tolerance. Basically, their body gets used to the drug and results are missing. It’s not uncommon for people to take more thinking it would be helpful.

Using the drug longer than necessary and increasing the dose can put you at a higher risk of phentermine withdrawal symptoms.

What Are Phentermine Withdrawal Symptoms?

Now that you know how withdrawal symptoms occur it’s time to mention what they are. As mentioned above, while studies show that phentermine doesn’t induce withdrawal symptoms users’ experiences say otherwise — many men and women who have been using this drug reported withdrawal symptoms after discontinuing its use. Below, you can see some of the most common withdrawal symptoms associated with this drug.


The most common withdrawal symptom that people experience is fatigue. You see, the drug acts as a stimulant to the central nervous system thereby increasing your blood pressure and boosting energy levels. When you suddenly stop taking the drug, the stimulating effect goes away, and there is no rise in energy and blood pressure.

As a result, you experience the opposite effects such as fatigue and lack of energy. This has a lot to do with the above-mentioned fact that the brain needs some time to adapt to the new situation once the use of phentermine has been discontinued.

Weight gain

Okay, this may seem odd to most people. Phentermine is one of the most widely used weight loss pills so how can it make you gain weight? This withdrawal symptom can occur due to a number of reasons. For example, other symptoms such as fatigue may make you reluctant to exercise regularly.

If you combine lack of physical activity with higher food intake, you get weight gain. The amount of weight you gain during this period depends on various factors such as length of treatment, lifestyle, and the phentermine dosage you have been taking (3).


Some patients reported that they experienced lightheadedness for three days after abruptly stopping phentermine use (4). It’s not quite clear why this withdrawal symptom occurs. Of course, it could be down to the sudden change in levels of neurotransmitters, but other symptoms may also play the role.

In addition, lightheadedness may also be a result of a change in blood pressure. Without stimulating effects, blood pressure can drop suddenly and make you feel dizzy and lightheaded.

Bad Mood

In order to curb appetite and help you lose weight, phentermine acts as a stimulant and directly influences neurotransmitters such as dopamine. These neurotransmitters are also responsible for your mood and pleasant emotions. Therefore, if you suddenly quit taking the drug, you may experience problems such as bad mood as your brain is trying to adjust. Some people may feel sad, depressed, and unmotivated during this time.

Phentermine cravings

Let’s say you want to quit chocolate (or you probably have), and you firmly decide it’s time to consuming it altogether. In the next few days, you’ll just keep craving that chocolate like your life depends on it. You want to experience that pleasure you get when eating chocolate.

Well, phentermine can work in the same way. Stimulating mechanism of action may make you want to seek that effect and then crave it if you stop taking the drug suddenly. Other phentermine withdrawal symptoms such as fatigue may also make you crave the drug because you’re well aware of the energy boost it provides.

Insomnia/sleep deprivation

Insomnia is both a common side effect and a withdrawal symptom associated with phentermine use or its cessation. The drug stimulates the central nervous system that keeps you alert and awake. That’s the reason why some people who take phentermine may complain about insomnia or sleep deprivation.

Insomnia occurs as a consequence of impaired levels of neurotransmitters and as a result of other withdrawal symptoms like bad mood and depression.

Other withdrawal symptoms

Besides the above-mentioned withdrawal symptoms people can also experience the following (5):

  • Cardiac arrest
  • Congestive heart failure
  • Diarrhea
  • Flatulence
  • Glaucoma
  • Headache
  • Heart palpitations
  • Irritability
  • Memory loss
  • Menstrual irregularities
  • Nerve damage
  • Seizures
  • Stomach pain
  • Stroke
  • Tremors
  • Vomiting

How to avoid phentermine withdrawal symptoms?

At this point we’ve covered reasons behind phentermine withdrawal symptoms and different effects people can experience, but is it possible to avoid them? The answer is – yes, but not always! Some people can’t avoid withdrawal symptoms, but they can minimize their severity and make them tolerable.

On the other hand, some people may avoid symptoms entirely. Like everything else this also depends on various factors including phentermine dosage, you’ve been taking. Here are some things you can do to avoid withdrawal symptoms if you want to stop taking the drug.

Use the drug for short-term only

Phentermine was specifically created for short-term use, but a major mistake that people make is that they want to continue taking the drug well beyond the end date. In order to avoid withdrawal symptoms make sure you take pills for short-term only. Your doctor will prescribe the drug and tell you for how long to take it. Don’t exceed that deadline.

Stick to the recommended dose

Doses provided by your doctor aren’t just for the show, they mean something. Instead of increasing the dose to experience desired effects it’s vital to take only as recommended by the physician. Higher dose increases the risk of withdrawal symptoms and unfortunate side effects.

Don’t go cold turkey

If you’ve been using phentermine for a while and it’s time to stop using it now you may need to be cautious about the way you do it. Going cold turkey would lead to frustrating withdrawal symptoms, particularly cravings. This is yet another subject where it’s important to listen to the doctor’s advice.

General practice is that doctor gradually decreases the dosage so you can eventually stop taking the drug without having to deal with withdrawal symptoms.

Adopt a healthy lifestyle

Phentermine isn’t a magic pill and a miraculous solution that would completely eliminate obesity. The drug may help you kick-start weight loss, but we tend to act as it can cure it. That explains why many people use phentermine without making any sort of change in their diet and exercise. So, when they stop taking the drug, all sorts of withdrawal symptoms may occur.

A practical way to avoid these symptoms is to modify your diet and strive to be more active. A healthy diet and regular exercise will improve your energy levels and exhibit a positive impact on your mood once you stop taking the drug.

Change your perception of phentermine

As long as you keep considering phentermine is a cure for your weight-related problems you’ll experience difficulties like symptoms mentioned above in this article. Instead of perceiving phentermine as the cure, you may need to look at it as a help or complementary tool that only assists in weight loss. That way you can lower your chances of seeking to experience the stimulating effect of the drug or other withdrawal symptoms.

Get enough sleep and manage stress

Sleep deprivation has a negative influence on your emotional and mental health. It increases cortisol levels which can deplete energy, paving the way to more severe problems like depression, and other withdrawal symptoms.

Therefore, a practical way to avoid phentermine withdrawal symptoms is to make sure you get enough good night’s rest and that you find a unique way to manage stress.


Phentermine is an effective weight loss pill, but due to stimulating effects, it may induce withdrawal symptoms in some people. Withdrawal symptoms occur when the brain is trying to adjust to the new situation. Persons experience symptoms such as fatigue, irritability, bad mood, among others. Adopting a healthier lifestyle and following doctor’s orders closely are good ways to avoid withdrawal symptoms or decrease their severity.