There are endless claims about treatments in the mass media, advertisements, and everyday personal communication. Some are true and some are false. Many are unsubstantiated: we do not know whether they are true or false. Unsubstantiated claims about the effects of treatments often turn out to be wrong. Consequently, people who believe and act on these claims suffer unnecessarily and waste resources by doing things that do not help and might be harmful, and by not doing things that do help. In response to these challenges, we developed the Informed Health Choices Key Concepts as the first step in the Informed Health Choices (IHC) project, an initiative supported by the Research Council of Norway. The aim of the IHC project and ongoing work by the IHC Network is to help people make informed health choices. In this document, we use the term “treatment” to include any intervention (action) intended to improve health, including preventive, therapeutic and rehabilitative interventions, and public health or health system interventions. Although we have developed and framed the Key Concepts to address treatment claims, people in other disciplines may find them relevant; for example, for assessing claims about the effects of educational interventions or environmental measures. The Informed Health Choices (IHC) Key Concepts serve as the basis for developing learning resources to help people understand and apply the concepts when claims about the effects of treatments (and other interventions) are made, and when they make health choices. They are also the basis for an item bank of multiple-choice questions (the Claim Evaluation Tools item bank) that can be used for assessing people’s ability to apply the IHC Key Concepts. The concepts are principles for evaluating the trustworthiness of treatment claims, comparisons, and choices. The concepts can help people to: Recognise when a claim about the effects of treatments has an untrustworthy basis Recognise when evidence from comparisons of treatments is trustworthy and when it is not Make well-informed choices about treatments They can help anyone, not just researchers, to think critically about whether to believe a treatment claim and what to do. This is sometimes referred to as critical health literacy. The Key Concepts are intended for people using research, not for doing research. In this update, we started with the explanations and implications from the 2019 version of the IHC Key Concepts. For each concept, we have provided one or more examples to illustrate each explanation, and the basis for each concept, drawing on relevant research that informed the development of the IHC Key Concepts. We have received only a few suggestions since the 2019 version was published and did not publish a new version of the Key Concepts in 2020 or 2021. We have decided that the version presented here will be the last revision made by us. This does not mean that this list of concepts cannot be further improved, but we will leave any further development of the IHC Key Concepts to others.