60% of adverse drug reactions are caused by herbal medicines

Cape Town | Scientists from the South African Medical Research Council’s (SAMRC) Biomedical Research and Innovation Platform (BRIP) in collaboration with Stellenbosch University have revealed a number of cases in which alternative treatments have altered the effects of prescription medication, either by diluting it, making it more potent or causing dangerous side effects.

The study reviewed 49 case reports and two previous observational studies, which detailed 15 cases of adverse drug reactions (ADR). The cases were analysed in order to ascertain whether ADRs and health complications were likely to have been caused by an interaction, based on the pharmacological properties of the active ingredients of the prescribed drug. It was concluded that 60% of the ADR cases were influenced by herbal medicines.

The co-usage of herbal medicines and prescribed medications is a common practice, especially in patients with hypertension, diabetes, cancer, seizures and depression. The study found some cases of acute rejection episodes in heart renal and liver transplant patients as a result of St John’s Wort (SJW), which is known to interact with drug metabolising enzymes. In another case, two patients with a history of generalised anxiety disorder and mild traumatic brain injury experienced serotonin syndrome and hypomania as a result of adding SJW and Ginkgo biloba to their treatment.

“The consequences of co-usage costs the patient their health and digs further into their pocket. It also places unnecessary strain on the health system as patients are sometimes readmitted into hospital for illnesses that could have been managed had they not engaged in co-usage,” says Professor Johan Louw, co-author and Director of the SAMRC’s Biomedical Research and Innovation Platform (BRIP).

Following an extensive review of medical literature to identify previous instances of patients suffering apparent adverse reactions, research by Dr Charles Awortwe, a Senior Scientist at BRIP has provided evidence of the damaging side effects associated with consuming herbal medicine alongside prescribed drug regimens for the treatment and management of cardiovascular diseases, cancer and renal transplants, HIV and chronic depression.

“The risk of herb-drug interactions is increasingly recognised as a public health problem which adds to the overall rapidly increasing global burden of non-communicable diseases. Patients’ deliberate refusal to disclose their use of herbal medicines to their doctors has led to underreporting which leaves us unaware of the true burden of critical herb-drug interaction cases,” indicated Dr Awortwe. 





Cardiovascular complications (coronary artery disease)

  • Warfarin
  • Statins (Atorvastatin, Simvastatin, Rosuvastatin)
  • Sage
  • Flaxseed
  • St John’ Wort
  • Cranberry
  • Goji juice
  • Green tea
  • Chamomilla
  • Sheg-Mai Yin

Renal transplant

  • Tacrolimus (immunosuppressant)
  • Cyclosporine A (immunosuppressant)
  • St John’ Wort
  • Turmeric
  • Chamomile Tea

HIV infection

  • Lopinavir
  • Ritonavir
  • Efavirenz
  • Nevirapine 
  • Ginkgo Biloba

Depression / seizure disorders

  • Venlafaxine
  • Sertraline
  • Ginkgo Biloba
  • Mentat
  • Celery Root

Cancer (Myeloid leukemia)

  • Imatinib
  • Panax Ginseng
  • Chokeberry Juice


Release date: 
Tuesday, March 13, 2018 - 10:53
Keletso Ratsela
Contact: Keletso Ratsela

Media Strategist
Tel: +27 71 214 5272
E-mail: keletso.ratsela@mrc.ac.za