Phenylethylamine vs. phentermine

Updated April 17, 2017

Phenylethylamine (PEA), commonly known as ephedrine, and phentermine are very similar in structure and function. In fact phentermine is a derivative of beta-phenylethylamine. Both phentermine and phenylethylamine can be used as an appetite suppressant, however there are notable differences to be aware of.


Both phentermine and phenylethylamine are closely related to amphetamines; however neither is considered an amphetamine. As you can see by the images of phenylethylamine and phentermine, they are very similar.


Phentermine triggers the hypothalamus region of the brain to release norepinephrine, epinephrine and dopamine. These neurotransmitters induce the "fight or flight" response, which eliminates the hunger signal. The desired effect of taking phentermine is the reduction in hunger.

Phenylethylamine increases the attention and activity in animals and has a profound effect on mood. Phenylethylamine increases the level of dopamine which induces feelings of bliss and happiness. Phenylethylamine is most commonly used to treat patients with depression; however. the effects on the chemicals of the brain also produce the effect of appetite control.


Phenylethylamine is a naturally occurring compound found in plants. Although the side effects induced have stimulated controversy among the medical community, it remains an uncontrolled substance. This means that it can be included in over-the-counter supplements. In the late 1990s, however, the U.S. Food and Drug Administration changed the classification of phentermine, making it a controlled substance because it has the ability to cause addiction.


The active ingredient in the popular weight loss supplement Fastin used to be phentermine. However, when the FDA required phentermine to be a prescription only medication, the manufacturer had to restructure the supplement. They changed the active ingredient to phenylethylamine, making it legal to continue selling over-the-counter. They also believed this change enhanced their product because phenylethylamine not only suppresses the appetite, but also elevates mood.

Side Effects

The most notable difference between phenylethylamine and phentermine is that phenylethylamine does not induce tolerance (meaning you have to take more for the same desired effect) or addiction. However, because both substances act in a similar fashion affecting neurotransmitters, they can induce similar side effects, including blurry vision, dry mouth, sleeplessness, irritability, upset stomach, increased blood pressure, nervousness, tiredness, confusion, headache, diarrhoea and skin rash. Phentermine can also induce depression, but phenylethylamine, commonly used to treat depression, does the opposite, actually lifting the mood.

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About the Author

Stephanie Chandler is a freelance writer whose master's degree in biomedical science and over 15 years experience in the scientific and pharmaceutical professions provide her with the knowledge to contribute to health topics. Chandler has been writing for corporations and small businesses since 1991. In addition to writing scientific papers and procedures, her articles are published on and other websites.