Table 2 The semi-structured in-depth interviews protocol

Risk perception and risk communication

1. Some people say that taking dietary supplements in different dosages might be effective, but if they are taken beyond these dosages they might have side effects. What is your opinion on this issue?

2. In your opinion, what is the benefit versus the risk of taking dietary supplements? What do you think are the benefits, and do the benefits exceed the risk?

3. For trainers only - As a trainer, do you warn your clients about possible risks?

The source of information and its reliability

1. What sources of information do you use to learn about dietary supplements?

2. Do you think the information is reliable?

The impact of environmental norms

1. Are there any dietary supplements in the gym where you work out? Please describe where they are located.

2. What do you think about it?

3. In your opinion, how does the presence of those supplements at the gym affect the gym members?

4. Does someone in your community (friends/gym members/ family members) use sports dietary supplements?

5. Who assists and directs them as to what kind of supplements they should take and what they are for?

6. Do you know about the consumption of supplements among trainers?

The authority status in the gym members’ point of view

1. In your opinion, which of the following agents (a physician /trainer /dietitian) influences a gym member, and in what order of importance?

2. If there was a case in which a trainer recommended one thing and a physician recommended another, to whom would you listen?

3. If a dietitian and a trainer recommended two different things, to whom would you listen? Why?