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Is Phentermine Speed? Is It an Amphetamine like Crystal Meth?

If you’ve ever wondered whether phentermine, a weight loss medication, is comparable to amphetamines or “speed,” the answer is a resounding no. While phentermine is classified as “amphetamine-like,” it is crucial to understand that it is not an amphetamine itself, nor does it belong to the same drug class as crystal meth or other amphetamines.

Phentermine shares some similarities with amphetamines in that it can bind to certain receptors in the brain and has comparable actions. However, a major difference lies in the release of dopamine – a neurotransmitter associated with pleasure and reward. Phentermine induces much lower dopamine release than drugs in the amphetamine class, which is one of the key reasons why it is not addictive like methamphetamine or cocaine.

The primary neurotransmitter released by phentermine is norepinephrine, with some impact on serotonin as well, while dopamine release is minimal. Consequently, phentermine’s appetite-suppressing effects, increased energy, and potential for insomnia may resemble those of amphetamines.

It is important to clarify that phentermine is not “speed.” Instead, it falls into the category of sympathomimetic amine anorectics, a type of stimulant utilized to reduce appetite in individuals with obesity. Though chemically similar to amphetamines, phentermine is distinguished by its low potential for addiction and abuse, leading to its classification as a Schedule IV drug. Understanding these distinctions is crucial in ensuring the safe and appropriate use of phentermine as a weight loss aid for those who need it.

What Is Phentermine ?

Phentermine is an isomer of methamphetamine and a sympathomimetic amine anorectic agent. It is chemically related to amphetamine and it is commonly referred to as an atypical amphetamine.

Is Phentermine Speed? Is It an Amphetamine like Crystal Meth?

Phentermine works by increasing the levels of certain neurotransmitters in the brain, such as dopamine and norepinephrine. These neurotransmitters are involved in regulating appetite and energy levels.

Phentermine is approved by the FDA for short-term use (up to 12 weeks) to help people lose weight. It is not a long-term solution for weight loss and should only be used under the supervision of a doctor.

Phentermine Side Effects

Phentermine, while effective as an appetite suppressant, may also come with some side effects that range from mild to moderate. It is essential to be aware of these potential adverse reactions to use the medication safely and responsibly.

Common Side Effects:

  1. Insomnia
  2. Increased Blood Pressure
  3. Dizziness
  4. Dry Mouth
  5. Nervousness
  6. Constipation
  7. Headache
  8. Itching
  9. Diarrhea

Severe Reactions:

In some cases, individuals may experience severe reactions that require immediate medical attention. These include:

  1. Swelling
  2. Confusion
  3. Dangerously High Blood Pressure
  4. Chest Pain
  5. Shortness of Breath

Possible Link to Pulmonary Hypertension:

A study published in the Yonsei Medical Journal examined the potential link between anorectic drugs, including phentermine, and pulmonary hypertension. The researchers reported a case of a 29-year-old woman who developed pulmonary hypertension after taking phentermine for five weeks. Although this is a single case, it raises the importance of monitoring and understanding potential risks associated with phentermine use.

Interactions with Alcohol:

Drinking alcohol while taking phentermine can intensify its side effects and may impair your ability to focus or remain alert. It is advisable to avoid alcohol consumption while using this medication and refrain from activities that require full attention, such as driving.

Is Phentermine Speed? Is It an Amphetamine like Crystal Meth?

If you experience any severe side effects or have concerns about phentermine’s impact on your health, seek immediate medical attention and consult with your healthcare provider. As with any medication, it is crucial to use phentermine responsibly and under proper medical supervision to minimize potential risks and ensure a safe weight loss journey.

The Risks of Phentermine and Its Potential for Addiction

Phentermine is a weight loss medication that comes with potential risks, particularly in terms of addiction and abuse. Understanding these dangers is crucial to using the medication safely and responsibly.

Habit-Forming Nature and Potential for Abuse:

Phentermine can be habit-forming and is known to be abused and diverted. As a result, it should not be prescribed to individuals with a history of substance use disorder. Abruptly stopping phentermine use may lead to withdrawal symptoms, including exhaustion and depression, especially in those who used the medication for an extended period. To avoid these reactions, if a person has taken phentermine for a long time, the dosage should be gradually decreased.

Warnings from the United Nations International Narcotics Control Board (INCB):

The INCB has cautioned phentermine users about its potential for addiction, particularly in individuals obsessed with becoming thin, especially women. Professor Hamid Ghodse, chairman of addiction psychiatry at St. George’s Hospital in London, described anorectic drugs, including phentermine, as highly addictive. Starting these drugs for weight loss might be easy, but it can also lead to dependence and addiction.

Short-Term Use and Potential Severe Side Effects:

Due to the declining effectiveness of phentermine over time and its potential for addiction, it is only approved for short-term use, typically for a period of 12 weeks or less. The severe side effects can become evident early on, but once the medication is stopped, individuals may likely regain the weight they initially lost. Therefore, phentermine should not be relied upon as the primary method for sustained weight loss.

The Dangers of Fen-Phen:

Phentermine was one of the ingredients in Fen-Phen, a weight loss drug that was removed from the market by the FDA in 1997 due to its association with serious cardiovascular problems. The combination of fenfluramine and phentermine was linked to heart and pulmonary emergencies, some of which resulted in fatalities.

Understanding the potential risks associated with phentermine use is vital in making informed decisions about weight loss strategies and ensuring that the medication is used responsibly under medical supervision.

Does Phentermine Speed Up Your Metabolism?

Phentermine is a stimulant medication that can potentially increase your metabolism. It does this by activating the central nervous system, which can lead to an elevation in metabolic rate. This means that your body will burn more calories at rest, which can help you lose weight. However, it is important to note that the extent of metabolic effects may vary among individuals. Some people may experience a significant increase in metabolism, while others may not see any difference at all.

Phentermine is primarily prescribed as an appetite suppressant rather than solely for its metabolic effects. This means that it is most effective for helping people lose weight by reducing their appetite. However, the increase in metabolism can be an added benefit for some people.

How Long Does Phentermine Last?

Phentermine is a medication that stays in your system for a long time, about 20 hours. This is called the half-life of phentermine. The half-life is the amount of time it takes for half of the medication to be eliminated from your body.

The long half-life of phentermine is why it is generally recommended to take it as early as possible in the morning. If you take it later in the day, it may interfere with your sleep. The stimulant properties of phentermine can make it difficult to fall asleep or stay asleep. By taking it earlier in the day, the medication has more time to metabolize and leave your system by bedtime.

Here is a table that summarizes the half-life of phentermine:

TimeAmount of Phentermine in Your System
0 hours100%
20 hours50%
40 hours25%
60 hours12.5%

As you can see, even after 60 hours, there is still a small amount of phentermine in your system. This is why it is important to talk to your doctor about whether phentermine is right for you, especially if you have any sleep problems.


In the quest for effective weight loss solutions, Phentermine has emerged as a potential ally. While it can increase metabolism and promote calorie burning, it is essential to recognize its primary role as an appetite suppressant. When used as part of a comprehensive plan, under the guidance of healthcare professionals, and with a balanced diet, Phentermine can be a valuable tool in achieving weight loss goals.

However, it’s crucial to approach Phentermine with caution, understanding its potential for addiction and abuse. Following prescribed dosages and timeframes is essential to minimize risks and side effects. Remember, Phentermine is a prescription medication and not classified as “legal speed.” Obtaining it through illicit means or without a valid prescription is unlawful and unsafe.


Meet Dinky, a Ramapo College of New Jersey alumnus who traded in her pen and notebook for a barbell and stopwatch. Dinky has been flexing her writing muscles for over four years as a journalist. She’s now bringing her expertise to, where she covers the latest and greatest in fitness trends, health, and lifestyle topics. But Dinky doesn’t just write about fitness – she lives it. She’s a regular at the gym and has a passion for CrossFit and bodybuilding competitions, making her the ultimate insider in the fitness industry. So whether you’re looking for workout inspiration, the latest supplement reviews, or coverage of the biggest competitions, Dinky’s got you covered.

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