Table 2.

TDF domains and categories identified in relation to nebulizer adherence

COM factor TDF domain	Category – factors related to adherence to nebulized treatment; n = number of participants reporting category out of 18 participants	Illustrative quotes (see supplementary table for further examples)
Capability
Knowledge	Having knowledge about treatment‐taking procedures (n = 16) Having knowledge about treatment action (how treatments work) (n = 11) Having knowledge about the importance of nebulizer treatment (n = 7) Having knowledge about treatment concerns (n = 3)	…you have to mix it up with like a liquid and then you have got to dissolve it, shake it, wait for it to settle and then pop it into the nebuliser (P10: L) DNase which is the stuff that thins out the mucus to be able to cough it up more easily… (P10: L)
Skills	Having good nebulizer skills (n = 14) Being able to concentrating on treatment taking (n = 5) Not having preparation or cleaning skills (n = 3)	I can hold my breath and I can do it exactly and I am one of the shortest times to take it like it takes 1–3 min (P5: VL) Like if I were going to have it now sort of … probably just, not saying I couldn't concentrate on other things but I just, I couldn't do it walking about (P18: H)
Memory, attention and decision processes	Ignoring reminders to take treatment (n = 9) Forgetting to take treatment (n = 7)	I think, I've tried alarms in the past and I tend to ignore those quite easily. (P4: VL) Get home later and it will completely slip my mind and I just forget to do it all together. (P2: VL)
Behavioural regulation	Struggling to plan treatment (n = 17) Having a plan for treatment or having a routine (n = 13) Knowing that others are monitoring nebulizer adherence (n = 12) Create prompts or cues for treatment (n = 9) Self‐monitoring nebulizer treatments (n = 6) Treatment is automatic or habitual (n = 5) Self‐monitoring health outcomes/symptoms (n = 5) Planning rewards for yourself for good adherence (n = 3)	we still struggle to get them all in to us on a daily basis … there's always sometimes a distraction or something happens like the unexpected (P4: VL) and sort of planning out when you're going to take it and things like that…that's sort of the main thing for me (P12: M) They said at hospital it weren't that bad but I, I, to me it were bad. It were like 50%, probably less…(P8: L)
Opportunity
Environmental context and resources	Having the time or capacity to do treatment (n = 16) Having the equipment/resources for treatment taking (n = 14) Weekends change the context for treatment (n = 13) Having an active social life as a barrier for treatment (n = 11) Holidays and travel as barriers to treatment (n = 11) Being able and willing to take treatment away from home or not (n = 11) The time of day can affect treatment (n = 10) Stressful or unusual events which are a barrier to adherence (n = 6) Multi‐tasking while doing treatment (n = 6) Hospital as a facilitator for treatment (n = 4) Distractions and interruptions to treatment (n = 4)	I'd say in the mornings is when I just do the Promixin because I haven't got time to do anything else (P10: L) That's a pain. We were camping and it was really hard to clean my neb properly. (P16: H) I do it but the circumstances of doing it like effect like my social life…(P7: M)
Social influences	Having support from family and others (n = 15) Having support from health care professionals (n = 11) Making social comparisons with others who have CF (n = 9) Experiencing conflict or nagging from others (n = 9) Being willing to take treatment in front of others or not (n = 8) Perceiving a lack of or limited support (n = 5) Experiencing conflict with health professionals (n = 3) Declining offers of support or avoiding support from others (n = 3)	Me friend when [name] comes she'll say ‘have you done your nebulizers today?’ just in a general chat (P3: VL) As soon as they got it I went up t'hospital for a separate appointment with one of physios and she taught me through it all. (P3: VL) I think it's more a case of as I say I know that's there's people who take more medication and things than what I do so (P9: L)
Motivation
Social/Professional role and identity	Being organized or disorganized (n = 7) Being obstinate or rebellious (n = 7) Having control over treatment taking (n = 6) Being a lazy person or not (n = 5) Being the kind of person who takes their treatment (n = 3)	…I've never really like planned things massively ahead so yeah I don't know… (P12: M) if I'm really stubborn about it then the more nagging the more it pushes me away… (P7: L)
Beliefs about Capabilities	Adherence to treatment is difficult (n = 16) Using a nebulizer is easy (n = 12) Adherence to treatment is easier with a routine (n = 10) Nebulizer treatment is an annoyance (n = 10) Adherence to treatment is especially difficult when tired (n = 7)	It's not that hard just blowing through a machine for 5 min before you go to bed, is it? (P18: H) Its physically making yourself do it …which is the thing (P7: L)
Optimism	Believing that complete (100%) adherence is unachievable (n = 8) Believing that complete (100%) adherence is achievable (n = 5) Being uncertain about whether 100% adherence is achievable (n = 4)	It's just life. It's never going to be absolutely hundred percent is it? (P16: H) It is though, it is because it is necessary and there is no excuse not, so it is achievable 100%… because it's necessary cos it's for your life (P14: M)
Beliefs about consequences	Nebulizer treatments are effective (n = 12) My health depends on me doing my nebulizer treatment (n = 12) Nebulizer treatment are not (always) effective (n = 9) Nebulizer treatments help my symptoms (n = 9) Nebulizer treatment has long‐term benefits (n = 7) Nebulizers are not the most important part of my CF treatment (n = 6) Occasional non‐adherence is OK (n = 6) Nebulizer treatment means I can avoid the need for IVs/Hospital stays (n = 5) If I feel OK I don't need to do my treatment (n = 5) Nebulizer treatments make me feel worse (n = 5) Bugs can become resistant to treatment (n = 3)	I do definitely think that all the nebulizer stuff is is a really good a really good drug to to have and a necessary one I think (P3: VL) …as long as I do my treatment I know that in a few weeks’ time you know 95% of the time I'm absolutely fine I can do whatever I like (P17: H) So it's like what's the point in taking all this medication if 6 months down the line let's say, it turns out that it's really done nothing, it's been a waste of time (P2: VL)
Reinforcement	Feeling better as a result of nebulizer treatment (n = 11) Not feeling that the nebulizer is working (n = 10) Experiencing negative effects of the nebulizer treatment (n = 8) Experiencing other rewards for adherence to treatment (e.g., improvements in lung function or praise from clinicians) (n = 5) Feeling worse as a result of not doing nebulizer treatment (n = 4) Experiencing negative consequences of non‐adherence to treatment (n = 4)	After a couple of days of being on it, I will cough more up, it does feel a lot thinner and my lungs feel clearer (P13: M) well you don't straight away but say you have like a week off, you will feel awful and your chest will hurt all the time (P6: L) DNase doesn't – I don't even notice any difference. I don't know if it does anything or not (P16: H)
Intention	Having an unstable intention for adherence or non‐adherence (only some of the time) (n = 14) Having a stable intention for adherence or non‐adherence (n = 13) Intending to change (improve) adherence (n = 11)	I do do it, whatever time I come in, and again, even if I'm drunk, which is very rare! (P16: H) maybe if I'm sort of going round there to someone's house and I'm staying one night, I'll maybe say ‘well I'll miss the night dose and I'll miss the morning dose’ (P13: M)
Goals	Having other life goals (n = 14) Having goals for the amount of treatment taken (n = 13) Having goals related to health outcomes (n = 13) Having goals that conflict with the ability to take treatment (n = 12) Not having or avoiding goals (n = 12)	I think that having kids makes me think that I don't wanna be ill… cos I have to be alive for them and well for them… (P16: H) Like if this time next year, if you can tell me it's still ninety five percent, I would be happy. You know what I mean? (P18: H)
Emotion	Experiencing low mood or depression (n = 8) Feeling regret or anticipating feeling regret (n = 5) Feeling fearful (n = 4) Avoiding thinking about CF or treatment (n = 4)	But now I mean I am trying to take it every morning but it's just yeah I think a lot of my medication at the minute is actually depression related why I can't take it (P5: VL) Because then because if I do get to that stage, which I've kind of accepted [I] am… I can, I can't look back and say I could have done better. (P15: H)