Published: 5 September 2014

Interaction Between Omeprazole and Citalopram/Escitalopram

Prescriber Update 35(3):41-42
September 2014

Key Messages

  • There is the potential for a pharmacokinetic and/or pharmacodynamic interaction between omeprazole and citalopram/escitalopram.
  • To reduce the risk of a patient experiencing an adverse event due to an interaction, the maximum recommended dose for citalopram is 20mg daily when omeprazole is being taken concurrently.

Interactions between medicines can occur through pharmacokinetic and pharmacodynamic mechanisms.

Omeprazole and citalopram/escitalopram are metabolised by cytochrome P450 (CYP) 2C19. Co-administration of omeprazole and citalopram doubled exposure to the S-isomer of citalopram1. Co-administration of omeprazole and escitalopram resulted in a 50% increase in plasma levels of escitalopram 1.

The pharmacokinetic interaction between omeprazole and citalopram/escitalopram increases the risk of QT prolongation, as this effect is associated with higher doses of citalopram2. The recommended maximum dose of citalopram is 20mg daily in patients who are also taking omeprazole3. Similarly a dose reduction of escitalopram may be needed in some patients also taking omeprazole 4.

Omeprazole and citalopram/escitalopram can each individually cause hyponatraemia. Therefore co-administration may increase the risk of hyponatraemia.

The Centre for Adverse Reactions Monitoring (CARM) has received six reports of hyponatremia in patients taking both omeprazole and citalopram/escitalopram. In four cases the patient's sodium level was close to the lower limit of normal on long term medicines including omeprazole, and experienced rapid falls within a week of adding citalopram/escitalopram. In one case severe hyponatraemia occurred within one week when omeprazole was added to long-term citalopram, with recovery when citalopram was discontinued. One patient experienced convulsions and two patients experienced confusion as a consequence of hyponatraemia. The majority of the patients were elderly, which is a known risk factor for developing hyponatraemia.

Caution is therefore advised when treating patients with omeprazole and citalopram/escitalopram concomitantly.

Please report any suspicions of drug interactions to CARM.

  1. AstraZeneca Ltd. Losec Modified Release Capsule Data Sheet. 13 January 2014. URL: (accessed 28 July 2014)
  2. Medsafe. 2012. Citalopram and Escitalopram - Similar Risk of QT Prolongation? Prescriber Update 33 (1): 3-4.
  3. Healthcare Logistics. Cipramil Data Sheet. 29 July 2013. URL: (accessed 28 July 2014)
  4. Mylan New Zealand Ltd. Loxalate Data Sheet. 3 April 2014. (accessed 28 July 2014)