Is Phentermine Speed? (same with amphetamines?)

January 9, 2024 |

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No, phentermine is not a speed drug.

All stimulant drugs or ‘uppers’ are not necessarily ‘speed’ drugs.

And the suspicion of the addiction potential that surrounds phentermine is what smears its reputation as an effective weight loss drug, which is also the main reason why it is confused with speed drugs.

Although both phentermine and speed drugs have the same mechanism of action, they are differently classified because they differ in the magnitude of stimulation and potential of abuse.

As you follow through this read, I will clarify the ambiguity you have regarding phentermine and speed by evaluating what science and actual user experience have to say about its safety and efficacy.

So, keep reading to find out the details.

What drug class is phentermine?

Phentermine belongs to the drug class of anorexiants and central nervous system stimulants.

Phentermine is an FDA-approved drug that works by suppressing appetite. It is prescribed to aid weight loss mostly in patients who suffer from co-morbidities like diabetes or blood pressure along with obesity.

Since phentermine is chemically and pharmacologically related to amphetamines so, it is presumed to have some potential for abuse. Thus you can only purchase it upon the doctor’s prescription, and treatment with it can only be pursued for a short term, about 8 to 12 weeks.

‘Speed’ is basically a street name for multiple stimulant drugs that speed up the system and get you high. They have high addiction potential, and this umbrella term mostly includes certain amphetamines, but it is more often associated with methamphetamine.

Phentermine, to be precise, is often wrongly suspected as a speed drug because of its relatedness to amphetamines.

One example of an amphetamine speed drug is ‘Adderall,’ which is a combination drug of two amphetamine salts, amphetamine, and dextroamphetamine.

It is classified as a speed drug because of its potential for abuse and causing withdrawal symptoms.

Although both phentermine and speed are central nervous system stimulants, the two are classified separately by the U.S. Drug Enforcement Agency (DEA).

Speed drugs are classified as schedule II stimulants because they have a high potential to cause addiction and withdrawal symptoms.

In contrast, phentermine is classified as a Schedule IV controlled substance as it has a low potential for abuse.

Some of its common withdrawal symptoms are psychosis, anxiety, depression, and drug cravings.

Speed drugs are a type of drug that can increase a person’s energy, focus, and alertness. They are also called “uppers” because they can make a person feel more awake and energetic.

Common speed drugs include amphetamines, methylphenidate, and cocaine.

They work by increasing levels of dopamine and norepinephrine in the brain, which leads to increased alertness and energy. However, they can also cause side effects such as anxiety, insomnia, and irregular heartbeat.

The fact that phentermine is not a speed drug may also be supported by scientific evidence since a clinical trial evaluated the addiction potential of phentermine and found no occurrence of withdrawal symptoms upon its abrupt cessation during its long-term therapy. However, subjects reported a loss of the phentermine’s appetite-suppressing benefit, but this is not a withdrawal symptom.

Does phentermine give you energy?

Yes, phentermine gives you an energy boost. Causing satiety and increased energy are two of the main effects that phentermine may induce in your body.

The reason is that the central and peripheral mechanisms control the energy balance and hunger, and phentermine targets exactly these systems to bring the desired weight loss effect.

The stimulant phentermine triggers the release of certain neurotransmitters like dopamine, adrenaline, and noradrenaline in the central nervous system and prevents their reuptake, which makes you feel full and energetic.

This energy buzz that you feel with the consumption of phentermine is supposed to be utilized in the gym for exercise because optimum weight loss with phentermine is possible when combined with diet and some physical activity.

Adrenaline is basically the major hormone that contributes to increasing the energy flow in your body.

And the stimulation of the fight and flight response by phentermine triggers the release of adrenaline.

One of the focuses of the fight and flight response is to make abundant energy available to the body so that you can fight the threat.

And thus, adrenaline promotes the fat-burning process and glucose production in the body for energy. Consequently, there is an increase in the blood flow to the muscles, and the lungs are filled with oxygen.

That way, your body is prepared to accommodate more activity and is charged enough to last you through a fistfight or a gym session.

According to an online poll, about 60% of the users feel buzzed after taking phentermine. If you want to know for how long this energy boost will last, then, according to Dr. Rick, you may expect it to last for over 10 to 15 hours.

Is phentermine a stimulant

Yes, phentermine is a stimulant.

I have already mentioned the effect of phentermine on different neurotransmitters, and according to the FDA as well, phentermine is a sympathomimetic amine.

Sympathomimetic drugs are stimulant compounds that activate the sympathetic nervous system by mimicking its endogenous agonists.

And thus, phentermine suppresses the appetite and promotes weight loss in obese individuals by acting on the central nervous system.

Phentermine vs Adderall

As you now already know that although both phentermine and Adderall are stimulants, the major difference between them is that one of them is a speed drug, but the other is not.

Moreover, for this section, I will go into the details of how you can compare these two, so scroll down without further ado.

Key Differences between Phentermine and Adderall

  • Phentermine is chemically and pharmacologically related to phentermine, but it is not an amphetamine drug. On the other hand, since Adderall is based on two amphetamine salts, it is the brand name for amphetamine
  • You may also differentiate the two drugs on the basis of their function since phentermine is primarily prescribed to treat obesity and promote weight loss. In contrast, Adderall is prescribed to treat Attention Deficit Hypersensitivity Disorder (ADHD)
  • These two drugs also differ in the magnitude of stimulation caused by them and their addiction potential. As mentioned in the sections above, phentermine is a Schedule II stimulant, whereas Adderall is a Schedule IV stimulant

Read more on Phentermine vs Adderall here.

Phentermine before and after

For this section, I have skimmed through some Reddit stories to give you an idea about what is the reputation of phentermine among various users.

Many users in a Reddit thread confirmed that phentermine helped them lose weight while they were on prescription because it made them less hungry.

But they mutually agreed to have gained a few pounds back when they stopped taking it since their appetite had come back.

For instance, ‘AveryAlmintoser’ wrote that she lost 90 pounds and went from 280 to 190 with phentermine but gained back 10 pounds in one year of discontinuing it.

‘Gmmiller’ reported that he lost about 30 Ibs by combining phentermine and keto diet in a year. Another user shared to have gone from 230 to 190 within 3 months of phentermine treatment but gained it all back after discontinuation.

Similarly, ‘Riverfaile’ also mentioned that he lost 30 pounds in three months without making significant changes in diet or exercise. One user shared to have lost 20 pounds on phentermine but had to take a break for 2 to 3 weeks during the course after hitting a plateau.

However, these users did not observe any side effects.

The reply by ‘Iaimtolose’ may summarize the experience shared by most users on this thread. He wrote that phentermine did not teach him how to keep weight off, and psychologically he was still a big guy, so eventually, his body caught up.

In a nutshell, your image before and after phentermine largely depends on how you manage your weight after discontinuing it, and the only significant difference you may see in your weight is while you are on prescription.

This implies that once your appetite returns after phentermine, you may gain back the lost weight and find no difference in your before and after progress.


To conclude, phentermine is not a speed drug. The reason is that users do not report increased dependence on it or any withdrawal symptoms.

However, you may grow a tolerance to it, and it may not induce the same effects it used to with long-term use.

Moreover, the weight loss benefit of phentermine is not sustainable since your hunger pangs will come back, and you may gain back all the weight you have lost after discontinuing the prescription.

Nonetheless, phentermine is a prescription drug, and you should not try to acquire it by illegal means and always consume it on a doctor’s recommendation.

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