Safety Concerns for Concurrent Use of Phentermine and Lorazepam

Mechanism of Concern

The Centers for Disease Control and Prevention recommends avoiding concurrent use of phentermine and lorazepam due to the significant risk of central nervous system depression, respiratory depression, and potentially fatal outcomes 1, 2
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 3, 4
Lorazepam is a benzodiazepine that causes central nervous system depression and can decrease respiratory drive 1, 2

The Centers for Disease Control and Prevention warns of an increased risk of potentially fatal overdose when benzodiazepines are combined with other central nervous system active medications 2
Case-cohort studies have found concurrent benzodiazepine use with other controlled substances to be associated with a near quadrupling of risk for overdose death 2

The Centers for Disease Control and Prevention recommends avoiding prescribing phentermine and lorazepam concurrently whenever possible 1, 2
If a patient is already on benzodiazepine therapy and requires weight management, the American Diabetes Association suggests considering alternative weight management medications that don't have stimulant properties 5
If a patient on phentermine requires treatment for anxiety, the Centers for Disease Control and Prevention recommends considering evidence-based psychotherapies, such as cognitive behavioral therapy, and non-benzodiazepine medications approved for anxiety 2

Patients with a history of substance use disorders are at particularly high risk with this combination 2
Patients with cardiovascular disease, hypertension, or psychiatric disorders should avoid this combination due to increased risks 4
If both medications are absolutely necessary, the Centers for Disease Control and Prevention suggests involving pharmacists and pain/psychiatric specialists in the management team, more frequent monitoring of vital signs and mental status, and using the lowest effective doses of both medications 1, 2, 6

Failing to check prescription drug monitoring programs for concurrent controlled medications prescribed by other clinicians can lead to adverse outcomes 2
Not recognizing that fatalities have been reported with concurrent use of benzodiazepines with other central nervous system active medications can result in inadequate monitoring and treatment 2, 6