Phentermine and topiramate and Zonisamide interaction
Phentermine and topiramate and Zonisamide: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Phentermine and topiramate label · effective 2026-05-18
Avoid use of phentermine and topiramate extended-release capsules with other carbonic anhydrase inhibitors.
If concomitant use of phentermine and topiramate extended-release capsules with another carbonic anhydrase inhibitor is unavoidable, the patient should be monitored for the appearance or worsening of metabolic acidosis.
Concomitant use of phentermine and topiramate extended-release capsules and a carbonic anhydrase inhibitor may increase the severity of metabolic acidosis and may also increase the risk of kidney stone formation [see Warnings and Precautions (5.10) ] .
Carbonic Anhydrase Inhibitors Clinical Impact Concomitant use of topiramate with any other carbonic anhydrase inhibitor may increase the severity of metabolic acidosis and may also increase the risk of kidney stone formation.
From the Zonisamide (ZONISADE) label · effective 2025-09-08
The risks of hyperammonemia and various manifestations of encephalopathy may be increased in patients treated with zonisamide and concomitantly taking other medications that can cause hyperammonemia, including valproic acid or topiramate [see Warnings and Precautions ( 5 )].
Patients should be carefully observed for signs of central nervous system (CNS) depression, such as somnolence and sedation, when ZONISADE is used with other drugs with sedative properties because of potential additive effects.
• ZONISADE should be used with caution if used in combination with alcohol or other CNS depressants ( 7.1 ).
CYP3A4 Inducers If co-administration with a potent CYP3A4 inducer is necessary, the patient should be closely monitored and the dose of ZONISAMIDE and other drugs that CYP3A4 substrates may need to be adjusted [see Clinical Pharmacology ( 12.3 )] .
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.