This is a Portuguese translation of the first in a series of 36 blogs explaining 36 Key Concepts we need to be able to understand to think critically about treatment claims. With thanks to Carlos Henrique dos Santos Oliveira and Cochrane Brazil for the translation. This blog explains that people often exaggerate the benefits of treatments and ignore or downplay potential harms. However, few effective treatments are 100% safe. Always consider the possibility that a treatment may have harmful effects.