Published: 6 December 2019

Publications

Liquorice – All sorts of side effects and interactions

Prescriber Update 40(4): 87
December 2019

The Centre for Adverse Reactions Monitoring (CARM) recently received a report of a man taking fludrocortisone who experienced very high blood pressure and panic attack (CARM ID: 133830). He had been taking fludrocortisone for a long period without problem. During assessment in hospital, the patient recalled that he had recently started eating liquorice.

Liquorice extract has mineralocorticoid-like effects

Liquorice (or licorice) extract is derived from the plant Glycyrrhiza glabra. Liquorice extract is used as a sweetener and as a flavouring agent in sweets and is also marketed as a dietary supplement¹.

Liquorice extract contains the compound glycyrrhizin. The active metabolites of glycyrrhizin, glycyrrhizic acid and glycyrrhetic acid, inhibit the metabolism of cortisol and bind to the mineralocorticoid receptor giving liquorice its mineralocorticoid-like activity¹. (Note that some liquorice sweets may be flavoured with anise oil instead of liquorice extract; anise oil does not contain glycyrrhizin.)

Potential side effects

Liquorice extract consumption can reduce blood potassium levels resulting in abnormal heart rhythms, high blood pressure, oedema, lethargy, heart failure and hypokalaemic myopathy manifesting as flaccid paralysis^1–3. In general, an upper limit of 100mg/day glycyrrhizin is recommended, which approximates to 60 to 70g of liquorice sweets¹.

Liquorice overconsumption should be suspected in people presenting with otherwise unexplained hypokalaemia and muscle weakness. The cortisol:cortisone ratio in the peripheral venous plasma is raised and there is a reduction in plasma renin and aldosterone level¹.

Sensitivity to glycyrrhizin is increased by prolonged gastrointestinal transit time, hypertension, and old age, and is more common in females¹.

Potential liquorice interactions

Pharmacodynamic interactions are possible with liquorice and fludrocortisone due to mineralocorticoid effects, and with liquorice and medicines that deplete potassium levels such as diuretics. Patients taking these medicines should avoid regular consumption of liquorice.

References

1. Omar HR, Komarova I, El-Ghonemia M, et al. 2012. Licorice abuse: time to send a warning message. Therapeutic Advances in Endocrinology and Metabolism 3: 125–38. DOI: 10.1177/2042018812454322 (accessed 25 September 2019).
2. FDA 2017. Black Licorice: Trick or Treat? URL: www.fda.gov/consumers/consumer-updates/black-licorice-trick-or-treat (accessed 25 September 2019).
3. Wichtl M (ed). 2004. Herbal Drugs and Phytopharmaceuticals : A Handbook for Practice on a Scientific Basis (3rd Edition). Stuttgart: Medpharm Scientific Publishers.