Is it safe for patients taking phentermine (anorexiant) to receive a steroid shot (corticosteroid injection)?

Phentermine and Steroid Injections: Safety Assessment

Direct Answer

Yes, patients taking phentermine can safely receive steroid injections—there are no documented drug interactions or contraindications between phentermine and corticosteroid injections. The primary concerns with phentermine relate to its cardiovascular effects and perioperative anesthetic risks, not interactions with corticosteroids.

Key Safety Considerations

No Direct Drug Interaction

• Phentermine is a sympathomimetic amine that works through norepinephrine release and has no pharmacologic interaction with corticosteroids 1
• The literature contains no reports of adverse interactions between phentermine and corticosteroid injections 2
• Corticosteroids do not affect phentermine metabolism or its cardiovascular effects 1

Cardiovascular Monitoring Remains Important

• Phentermine can increase heart rate and blood pressure, requiring periodic monitoring regardless of steroid administration 1, 3
• Patients with uncontrolled hypertension or active cardiovascular disease should avoid phentermine entirely, but this is unrelated to steroid injection safety 1
• If the patient has stable cardiovascular status on phentermine, adding a steroid injection poses no additional interaction risk 4

Documented Phentermine Drug Interactions to Avoid

The actual concerning interactions with phentermine include:

• Monoamine oxidase inhibitors (MAOIs)—absolute contraindication within 14 days 1, 4
• Other sympathomimetic amines like phenylpropanolamine (severe interaction risk) 2
• Tramadol (most frequently co-prescribed drug with severe interaction potential) 2
• Dextromethorphan (moderate interaction) 2

Perioperative Considerations

• If the steroid injection is being given as part of a surgical procedure requiring general anesthesia, discontinue phentermine at least 4 days prior to surgery due to risk of refractory hypotension with anesthetic agents 5
• This recommendation is specific to general anesthesia, not the steroid injection itself 5
• For simple office-based steroid injections without general anesthesia, no phentermine discontinuation is necessary 5

Clinical Algorithm

For office-based steroid injection (no general anesthesia):

• Proceed with steroid injection while patient continues phentermine 1
• Ensure blood pressure is controlled (not specifically related to the injection) 1

For steroid injection with general anesthesia:

• Stop phentermine at least 4 days before the procedure 5
• Warn anesthesiologist about recent phentermine use, as hypotension may be unresponsive to ephedrine 5
• Use direct-acting vasopressors if hypotension occurs 5

Common Pitfalls to Avoid

• Do not confuse phentermine's cardiovascular monitoring requirements with contraindications to steroid injections—these are separate safety concerns 1, 3
• Do not unnecessarily discontinue phentermine for simple steroid injections that don't involve general anesthesia 5
• Be aware that corticosteroids may cause hyperglycemia and weight gain, which could counteract phentermine's weight loss effects, but this is not a safety contraindication 1