Phentermine

What is/are Phentermine?

Phentermine, a contraction of "phenyl-tertiary-butylamine", is a psychostimulant drug of the phenethylamine class, with pharmacology similar to amphetamine. It is used medically as an appetite suppressant.

It is approved as an appetite suppressant to help reduce weight in obese patients when used short-term and combined with exercise, diet, and behavioral modification. It is typically prescribed for individuals who are at increased medical risk due to their weight.

Medical uses

Phentermine is used for the short-term treatment of obesity.

Adverse effects

Generally, phentermine appears to be relatively well tolerated. It can produce side effects consistent with its catecholamine-releasing properties, e.g., tachycardia (increased heart rate) and elevated blood pressure, but the incidence and magnitude of these appear to be less than with the amphetamines. Because phentermine acts through sympathomimetic pathways, the drug may increase blood pressure and heart rate. It may also cause palpitations, restlessness, and insomnia. Additionally, phentermine has the potential to cause psychological dependence.

After short-term use, tolerance begins and can be followed by rebound weight gain. Long term data for use of phentermine shows no net weight loss.

Cardiovascular side effects include palpitations, tachycardia, and elevation of blood pressure. In the central nervous system, it can cause overstimulation, restlessness, dizziness, insomnia, euphoria, dysphoria, tremor, and headache. Its gastrointestinal effects include dryness of the mouth, unpleasant taste, diarrhea, constipation, and other gastrointestinal disturbances. It may also cause allergic effects - urticaria and changes in libido.

Its less common, but more severe, side effects include:

•     Convulsions (seizures)
•     Fever
•     Hallucinations
•     Agitation and aggression
•     Bizarre behavior
•     Mental or mood changes
•     Exaggerated sense of well-being
•     Increased blood pressure
•     Severe or persistent light-headedness, fainting or headache
•     Periods of mania followed by period of depression
•     Fast or irregular heartbeat
•     Overactive reflexes
•     Tremors, trembling or shaking
•     Panic
•     Restlessness
•     Severe nausea, vomiting or diarrhea
•     Stomach cramps
•     Weakness
•     Constipation
•     Primary pulmonary hypertension
•     Regurgitant cardiac valvular disease
•     Pounding in the chest or shortness of breath

Cautions

Phentermine use is contraindicated in those who are:

•     Allergic to phentermine, any of its metabolites or other sympathomimetics (e.g., pseudoephedrine)
•     Taking amphetamine (i.e., Adderall, Dexedrine, Vyvanse), dexfenfluramine, fenfluramine, furazolidone, guanadrel, guanethidine, or have taken a monoamine oxidase inhibitor (MAOI) (e.g., phenelzine) in the last 14 days
•     Subject to severe high blood pressure, an overactive thyroid, glaucoma, heart or blood vessel disease, severe narrowing of the blood vessels, diabetes, a brain or spinal cord disorder, hardening of the arteries, or high cholesterol or lipid levels
•     In an agitated state, or have a history of substance abuse
•     Pregnant, planning to become pregnant, or are breast-feeding

Medicines which may interact with phentermine, such as dexfenfluramine, fenfluramine, furazolidone, or MAOIs (e.g., phenelzine) are contraindicated because of the risk of serious side effects, such as increasing headache, high blood pressure, slow heart rate, elevated temperature, or possibly fatal lung problems, may be increased. Guanadrel (Hylorel) or guanethidine (Ismelin) effectiveness may be decreased by phentermine. Antacids may decrease the excretion of phentermine.[3] Carbonic anhydrase inhibitors (acetazolamide, dichlorphenamide, methazolamide) may decrease the excretion of phentermine.[ 

Mechanism of action

Phentermine works on the hypothalamus portion of the brain to stimulate the adrenal glands to release norepinephrine, a neurotransmitter or chemical messenger that signals a fight-or-flight response, reducing hunger. Phentermine works outside the brain, as well, to release epinephrine or adrenaline, causing fat cells to break down stored fat, but the principal basis of efficacy is hunger-reduction. At clinically relevant doses, phentermine also releases serotonin and dopamine, but to a much lesser extent than that of norepinephrine.

This article uses material from the Wikipedia article Phentermine, which is released under the Creative Commons Attribution-Share-Alike License 3.0.