Is it safe to use phentermine (anorectic) and lorazepam (benzodiazepine) concurrently?

Phentermine and Lorazepam: Safety Concerns for Concurrent Use

Concurrent use of phentermine and lorazepam is not recommended due to the significant risk of central nervous system depression, respiratory depression, and potentially fatal outcomes. 1

Mechanism of Concern

• Benzodiazepines (like lorazepam) and stimulants (like phentermine) have opposing effects on the central nervous system, creating unpredictable physiological responses 1
• Phentermine is a sympathomimetic amine anorectic that stimulates the central nervous system, increasing blood pressure and heart rate 1
• Lorazepam is a benzodiazepine that causes central nervous system depression and can decrease respiratory drive 1
• This combination can lead to dangerous fluctuations in vital signs and neurological status 1

Specific Risks

• Increased risk of potentially fatal overdose when benzodiazepines are combined with other central nervous system active medications 1
• Case-cohort studies have found concurrent benzodiazepine use with other controlled substances to be associated with a near quadrupling of risk for overdose death 1
• Phentermine may reduce the sedative effects of lorazepam, potentially leading to unpredictable clinical responses 2
• The combination may increase the risk of cardiovascular side effects, including arrhythmias 3

Clinical Guidance

• Avoid prescribing phentermine and lorazepam concurrently whenever possible 1
• If a patient is already on benzodiazepine therapy and requires weight management:
  • Consider alternative weight management medications that don't have stimulant properties 1
  • Non-pharmacological approaches like diet and exercise should be prioritized 3
• If a patient on phentermine requires treatment for anxiety:
  • Consider evidence-based psychotherapies (e.g., cognitive behavioral therapy) 1
  • Consider non-benzodiazepine medications approved for anxiety 1

Special Considerations

• Patients with a history of substance use disorders are at particularly high risk with this combination 1
• Patients with cardiovascular disease, hypertension, or psychiatric disorders should avoid this combination due to increased risks 1, 2
• If both medications are absolutely necessary (which is rare), consider:
  • Involving pharmacists and pain/psychiatric specialists in the management team 1
  • More frequent monitoring of vital signs and mental status 1
  • Using the lowest effective doses of both medications 1

Common Pitfalls

• Assuming that because one medication is for weight loss and another for anxiety, they won't interact significantly 2
• Failing to check prescription drug monitoring programs for concurrent controlled medications prescribed by other clinicians 1
• Not recognizing that fatalities have been reported with concurrent use of benzodiazepines with other central nervous system active medications 1
• Underestimating the additive adverse effects when these medications are combined 3