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What Is Phentermine HCl?

By S. Berger
Updated May 17, 2024
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Phentermine is a medication in the amphetamine drug family used to assist patients with losing weight, especially when other medications and techniques, like diet and exercise, have not been successful. The name phentermine HCl refers to the fact that this drug is sold in its hydrochloride salt form, which keeps the molecule stable and helps it to absorb more easily into the body. Due to its side effects and potential for abuse, it is usually only recommended for short periods of time to rapidly lose weight, until a more sustainable weight-loss plan can be created between the doctor and patient.

Like other amphetamine-class drugs, phentermine HCl reduces feelings of hunger by acting on the central nervous system (CNS). Patients usually must diet and exercise regularly while taking this medication to achieve a maximum benefit from it. It exerts its effects on the body for about 15 to 30 hours, meaning that taking a daily dose in the morning can usually suffice to control appetite all day.

Most medications have some side effects inherent with their use, and phentermine HCl is no exception. This drug is well-tolerated by most patients, meaning that many people taking it experience few, if any, side effects. Diarrhea, nausea, dry mouth, and insomnia are the most commonly seen side effects with this drug. Patients usually gain a tolerance to these effects within days of taking this stimulant, and they should not be a cause for concern unless they last for an extended period of time, or are extremely severe.

Occasionally, more problematic side effects can occur in patients taking phentermine HCl. Such effects can include a rise in blood pressure, irregular heart beat, chest pain, and tremors. In the event that these side effects occur, emergency medical services should be contacted immediately, since they may actually be a sign of a major health problem. Allergic reactions causing shortness of breath or swelling of the face also require medical attention.

Interactions with other medications can also occur when taking Phentermine HCl. Taking this medication within weeks of certain antidepressants, including selective serotonin reuptake inhibitors (SSRIs) or monoamine oxidase inhibitors (MAOIs) may lead to dangerously high levels of certain neurotransmitters, causing a variety of effects. Other stimulants should be avoided while taking phentermine HCl, in order to avoid potentially harmful high blood pressure or tachycardia, an elevated heart beat. Sleeping pills and CNS depressants, including alcohol, can increase this drug's effect on mood.

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