Drug-related problems are frequent and may result in reduced quality of life, and even morbidity and mortality. Many studies have shown that clinical pharmacists can effectively identify and prevent clinically significant drug-related problems and that physicians acknowledge and act on the clinical pharmacist's suggestions for interventions to the drug-related problems. A pro-active rather than a reactive approach on the part of the pharmacists seems prudent for obtaining most benefit. This includes participation of pharmacists in the multidisciplinary team discussions - at the stage of ordering and prescribing - where all types of drug-related problems, including also potential problems, should be discussed. In addition, counselling by pharmacists about medication on discharge and follow-up after discharge resulted in better outcomes. Furthermore, clinical pharmacists can positively influence other outcomes, such as improvement of levels of markers for drug use (e.g. optimization of lipid levels, anticoagulation levels and blood pressure). Some studies have reported positive effects on hard clinical outcomes, such as reduced length of stay, fewer re-admissions and fewer disease events (e.g. heart failure events and thromboembolism). However, more studies should be undertaken with larger patient populations, including patients from multiple sites. More knowledge about patient-specific factors that predict improved care is also needed. In conclusion, there is increasing evidence that participation and interventions of clinical pharmacists in health care positively influence clinical practice.