PURPOSE: The aim of this overview of systematic reviews is to summarise and critically evaluate the evidence from systematic reviews of the adulteration and contamination of herbal medicinal products (HMPs). METHODS: Five electronic databases were searched to identify all relevant systematic reviews. RESULTS: Twenty-six systematic reviews met our inclusion criteria. The most commonly HMPs were adulterated or contaminated with dust, pollens, insects, rodents, parasites, microbes, fungi, mould, toxins, pesticides, toxic heavy metals and/or prescription drugs. The most severe adverse effects caused by these adulterations were agranulocytosis, meningitis, multi-organ failure, perinatal stroke, arsenic, lead or mercury poisoning, malignancies or carcinomas, hepatic encephalopathy, hepatorenal syndrome, nephrotoxicity, rhabdomyolysis, metabolic acidosis, renal or liver failure, cerebral edema, coma, intracerebral haemorrhage, and death. Adulteration and contamination of HMPs were most commonly noted for traditional Indian and Chinese remedies, respectively. CONCLUSIONS: Collectively these data suggest that there are reasons for concerns with regards to the quality of HMPs. Adulteration and contamination of HMPs can cause serious adverse effects. More stringent quality control and its enforcement seem to be necessary to avoid health risks.