Fentermina, a brand name for a formulation containing essential Phentermine, is widely used for various health benefits. This guide provides comprehensive information on the uses, dosage, side effects, and mechanism of action of Fentermina, as well as insights into how long it takes to work. Understanding these aspects can help you make informed decisions about its use and effectiveness.


Fentermina is a sympathomimetic amine commonly used as an appetite suppressant for short-term weight reduction.

Uses For

Fentermina is used in the management of obesity, including weight loss and maintenance of weight loss.

Mechanism of Action

The mechanism of action of phentermine in treating obesity is not fully understood, but believed to involve release of norepinephrine and dopamine in the hypothalamus, which are two of the neurotransmitters involved in controlling hunger.

How Long Does It Take to Work?

Fentermina can begin to work immediately, with some patients noticing results within an hour. Generally, the full effects of the drug can be felt within a few days of starting a course of treatment.


Fentermina is rapidly absorbed after oral administration, with peak levels occurring approximately 1 to 4 hours after administration.

Route of Elimination

Fentermina is mostly eliminated via hepatic metabolism and urinary excretion.


The maximum daily dose of phentermine is 37.5 mg given in two divided doses of 18 to 25 mg. This dose should not be exceeded. Dosage may be tailored to the individual patient's needs.


Fentermina should be taken once a day, one hour before meals, on an empty stomach. It should be taken with plenty of water to prevent dehydration. It should not be taken with alcohol or other CNS depressants.

Side Effect

Common side effects of phentermine include dry mouth, constipation, difficulty sleeping, headache, and dizziness. Rare side effects can include impaired sexual function, depression, and abuse and dependence.


Fentermina can be toxic in high doses, leading to symptoms such as high blood pressure, palpitations, confusion, tremors, and agitation.


Fentermina should be used with caution in patients with heart conditions, hyperthyroidism, a history of drug or alcohol abuse, and those taking other medications such as monoamine oxidase inhibitors (MAOIs). It is not typically recommended for pregnant or nursing women, or children.


Drugs that can interact with phentermine includes tricyclic antidepressants, other appetite suppressants, MAOIs, warfarin, amitriptyline, doxepin, nortriptyline, haloperidol, fluphenazine, and phenytoin.

Disease Interaction

Patients with pulmonary hypertension, chest pain, high blood pressure, an overactive thyroid, increased intra-ocular pressure, or diabetes should not use phentermine.

Drug Interaction

Patients taking monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants, or other appetite suppressants should not take phentermine. In addition, patients taking antihypertensive medications, digoxin, lithium, alcohol, or benzodiazepines may experience adverse reactions when taking phentermine.

Food Interactions

Fentermina should be taken on an empty stomach, one hour before meals. Eating a meal with phentermine can reduce the drug's potency and delay absorption.

Pregnancy Use

Fentermina should not be used by pregnant women. Data regarding use in lactation is limited; however, it is not recommended for use in nursing mothers.

Acute Overdose

Symptoms of an acute overdose of phentermine can include loss of appetite, increased heart rate, dizziness, disorientation, agitation, confusion, tremors, and seizures. It is important to seek immediate medical attention in the case of an overdose.


Fentermina is contraindicated in patients who are pregnant, nursing, or have a history of heart disease, hyperthyroidism, glaucoma, or a history of drug or alcohol abuse.

Use Direction

Fentermina should be taken as directed by a healthcare professional. It is generally prescribed to be taken once a day, one hour before meals, on an empty stomach. It should be taken with plenty of water to prevent dehydration. Tablets should be swallowed whole, and not crushed or chewed.

Storage Condition

Fentermina should be stored at room temperature, in a dry and dark area, and away from heat and moisture. It should be kept out of the reach of children and pets.

Volume of Distribution

The apparent volume of distribution of phentermine is 10 - 11 L/kg.

Half Life

The terminal half-life of phentermine is about 21 hours.


The apparent clearance of phentermine is 0.5 L/h/kg.

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