According to the World Health Organization, counterfeit medicines are medicines that are mislabeled deliberately and fraudulently regarding their identity and/or source. All kinds of medicines have been counterfeited, both branded and generic ones. Counterfeit medicines may include products containing correct or wrong ingredients; without active or with insufficiently or over-active ingredients, or with fake packaging. Many sources of information have been explored, including reports from the national medicine regulatory authorities, pharmaceutical companies and literature data. Since the time counterfeit drugs first appeared, they have become more sophisticated and more difficult to be detected. The World Health Organization estimate is that up to 1% of medicines available in the developed world are likely to be counterfeit. This figure rises to 10% globally, although in some developing countries it is 50%. The World Health Organization estimate is that 50% of medicines available via the internet are counterfeit. The knowledge about counterfeit drugs should be used to educate students of pharmacy and medicine, health professionals and patients. The most important players in campaign against counterfeit medicines are health professionals. Pharmacists and doctors should stay vigilant and report suspicious products, and consider counterfeits as a possible cause of adverse reactions or therapeutic failure. Patients should inform their pharmacists and doctors if they suspect any irregularity concerning their medication, if they experience side effects or a decrease in beneficial effect. The crucial step in the prevention of counterfeit medicines is to get supplied from reliable sources, i.e. licensed pharmacies.