What are the side effects of phentermine (Adipex-P)?

From the Guidelines

Phentermine can cause several side effects, including dry mouth, insomnia, constipation, headache, increased heart rate, elevated blood pressure, nervousness, restlessness, and dizziness, as reported in the most recent study 1.

Common Side Effects

The most common side effects of phentermine include:

• Dry mouth
• Insomnia
• Constipation
• Headache
• Increased heart rate
• Elevated blood pressure
• Nervousness
• Restlessness
• Dizziness These side effects are related to the increased sympathetic nervous system activity caused by phentermine, as stated in the study 1.

Serious Side Effects

More serious side effects that require immediate medical attention include:

• Chest pain
• Shortness of breath
• Swelling in the legs or ankles
• Fainting
• Severe mood changes or thoughts of suicide It is essential to note that phentermine may also cause psychological dependence and withdrawal symptoms when stopped abruptly, as mentioned in the study 1.

Special Considerations

Patients with heart disease, uncontrolled high blood pressure, hyperthyroidism, glaucoma, or a history of drug abuse should avoid phentermine, as stated in the study 1. Additionally, phentermine should not be taken with MAO inhibitors or other appetite suppressants, as reported in the study 1. If you experience severe side effects while taking phentermine, contact your healthcare provider immediately. The recommended dosage of phentermine is 15 to 37.5 mg orally once daily in the morning, as stated in the study 1.

From the FDA Drug Label

The following adverse reactions to phentermine have been identified: Cardiovascular: Primary pulmonary hypertension and/or regurgitant cardiac valvular disease, palpitation, tachycardia, elevation of blood pressure, ischemic events. Central Nervous System: Overstimulation, restlessness, dizziness, insomnia, euphoria, dysphoria, tremor, headache, psychosis Gastrointestinal: Dryness of the mouth, unpleasant taste, diarrhea, constipation, other gastrointestinal disturbances. Allergic: Urticaria. Endocrine: Impotence, changes in libido.

The side effects of phentermine (Adipex-P) include:

• Cardiovascular side effects such as primary pulmonary hypertension, palpitation, and elevation of blood pressure
• Central Nervous System side effects such as overstimulation, restlessness, and insomnia
• Gastrointestinal side effects such as dryness of the mouth and diarrhea
• Allergic reactions like urticaria
• Endocrine side effects including impotence and changes in libido 2 2

From the Research

Side Effects of Phentermine

The side effects of phentermine (Adipex-P) can be categorized into several groups, including:

• Cardiovascular side effects:
  • Hypertension 3
  • Vasoconstriction 3
  • Vasculopathy 3
  • Valvular heart disease, particularly when used in combination with fenfluramine 4
  • Pulmonary hypertension 4
  • Ischemic colitis, a rare but potentially serious side effect 5
• Neurological and psychological side effects:
  • Mental illness, observed in some individuals 3
  • Cognitive impairment 5
• Gastrointestinal side effects:
  • Diarrhea 5
• Other side effects:
  • Palpitations 6
  • Increased heart rate or blood pressure 5

Drug Interactions

Phentermine can also interact with other medications, leading to potential drug-drug interactions (PDDIs) and adverse drug reactions (ADRs) 7. The risk of PDDIs is higher when phentermine is used for long-term periods, exceeding 12 consecutive weeks 7. Common medications that may interact with phentermine include:

• Dextromethorphan, which can cause moderate PDDIs 7
• Tramadol, which can cause severe PDDIs 7
• Formoterol, which can cause moderate PDDIs 7
• Phenylpropanolamine, which can cause severe PDDIs 7