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Here are some of the side effects you may experience using prescription phentermine.

Side effects
Generally, phentermine appears to be relatively well tolerated.[3] 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 physical and psychological dependence.

More Common Symptoms

• Insomnia
• Increased blood pressure
• Irritability
• Nervousness
• Sense of well-being

Less Common to Rare Symptoms - See more

• Blurred vision
• Change in sexual desire
• Clumsiness
• Confusion
• Diarrhea
• Dizziness
• Dry mouth
• Headache
• Irregular heartbeat
• Nausea or vomiting
• Psychosis
• Skin rash or itching
• Stomach pain
• Tiredness
• Unpleasant taste
• Possible Overdose Symptoms
• Confusion
• Convulsions (seizures)
• Dizziness
• Fast Breathing
• Fever
• Hallucinations
• Hostility with urge to attack
• Irregular blood pressure
• Irregular heartbeat
• Lightheadedness or Fainting
• Mental Depression, following a period of excitement
• Tremors, Trembling, or Shaking
• Overactive Reflexes
• Panic
• Restlessness
• Severe nausea, vomiting or diarrhea
• Stomach cramps
• Tiredness or Weakness

Contraindications and warnings

Patients with the following should not use Phentermine:

• An allergy to any ingredient in Phentermine or other sympathomimetics (eg, pseudoephedrine)
• Are also taking dexfenfluramine, fenfluramine, furazolidone, guanadrel, guanethidine, or have taken a monoamine oxidase inhibitor (MAOI) (eg, phenelzine) in the last 14 days
• Have severe high blood pressure, an overactive thyroid, glaucoma, heart or blood vessel disease, or severe narrowing of the blood vessels
• Are in an agitated state, or have a history of substance abuse

Some medical conditions may interact with Phentermine, patients with the following should consult with their doctor before using phentermine:

• Are pregnant, planning to become pregnant, or are breast-feeding
• Are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
• Have allergies to medicines, foods, or other substances
• Have a brain or spinal cord disorder, hardening of the arteries, high blood pressure, diabetes, or high cholesterol or lipid levels

Some medicines may interact with Phentermine, such as the following:

• Dexfenfluramine, fenfluramine, furazolidone, or MAOIs (eg, phenelzine) because 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
• Serotonin specific reuptake inhibitors (eg, fluoxetine) because the risk of their side effects may be increased by Phentermine
• Guanadrel or guanethidine because their effectiveness may be decreased by Phentermine

External Links

Medline Plus / About Phentermine

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