May 2022
Marion Déléaval, MD Haran Burri, MD Elise Bakelants, MD

Key Teaching Points

• Herbal supplements are gaining popularity and are often perceived as harmless because of their “natural” character. However, the use of these supplements may be associated with considerable side effects.
• Data concerning the effectiveness, toxicity, and potential for interactions of herbal supplements are limited.
• Dosing recommendations should always be respected and possible interactions with other medication or supplements should be considered.


Herbal supplements are gaining popularity and are often perceived as harmless because of their “natural” character. Indeed, although available without prescription, these preparations contain mixtures of substances that can have significant physiological effects. The potential negative side effects are often not foreseeable, as the exact composition of the preparation can vary greatly from one distributor to another, and because the pharmacodynamic and pharmacokinetic properties of these molecules are not well known. We describe the case of a 56-year-old woman with acquired long QT syndrome, torsades de pointes, and syncope following the use of herbal supplements.

Case report

A 56-year-old woman was admitted to the emergency department for syncope without prodromes in a supine position. This was the first episode of syncope, but she had experienced 3 prolonged episodes of dizziness over the past month. Her medical history was unremarkable. There was no familial history of sudden cardiac death. For 4 months, she had been taking hemp oil, containing the cannabinoid derivatives cannabidiol (CBD) (61 mg/mL in 1 supplement and 24 mg/mL in the other) and cannabigerol (CBG) (1 mg/mL in 1 supplement), 3–4 times daily because of a stressful work-life balance. The physical examination was normal, apart from hypotension (86/42 mm Hg). Her blood chemistry showed normal kidney function, a magnesium concentration at the lower limit of normal, and a normal potassium level. A toxicology screen was not performed. A rhythm strip showed short runs of torsades de pointes (Figure 1). She received intravenous magnesium and saline fluids in the emergency department with stabilization of the heart rhythm. The 12-lead ECG showed normal sinus rhythm at 58 beats per minute and a markedly prolonged corrected QT (QTc) interval of 667 ms (according to the Bazett formula, Figure 2).