Iomax

Adverse effects

Generally, phentermine appears to be relatively well tolerated.[2] 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.

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:[citation needed]

Convulsions (seizures)
Fever
Hallucinations
Hostility with urge to attack
Bizarre behavior
Mental or mood changes
Exaggerated sense of well-being
Irregular 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), bupropion (WellButrin), 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
Taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement

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.[3]