The search resulted in 17 studies for synthesis; the flow of studies is outlined in Fig. 1. All study characteristics and quality indicators are detailed in Additional files 1, 2, 3 and 4. Of the 17 studies, 8 were conducted in the USA [27,28,29,30,31,32,33,34], 4 in the UK [9, 35,36,37], 2 in Canada [38, 39] and 1 each in the Netherlands [40], Australia [41], and Sweden [42]. Twelve of the studies were reported in journal articles [9, 27, 30, 32,33,34,35, 38,39,40,41,42] and 5 were part of doctoral research [28, 29, 31, 36, 37]. Eight of the studies used qualitative methodology [9, 27, 28, 31, 34, 36, 37, 42], 6 were quantitative [29, 30, 33, 38,39,40] and 3 used mixed methods [32, 35, 41]. Methods used in the qualitative work included grounded theory [32, 36] thematic analysis [41, 42] phenomenology [28, 31] and framework analysis [9]. Quantitative studies employed cross-sectional survey design and used a variety of descriptive statistics [29, 30, 32, 33, 35, 39,40,41] correlational analysis [41] and regression analysis [29, 33, 35, 40].

Fig. 1 PRISMA flowchart. *Two articles identified through searching of reference lists of included articles so not included in earlier stages of the review Full size image

All participants in the studies resided within the community and had either a diagnosed serious mental health condition [9, 30,31,32, 38, 39], mental health problems associated with a physical health condition [29, 33,34,35, 40, 41], mental health problems associated with a developmental disorder [37, 42] or self-reported mental health conditions [27, 28]. Two of the studies involved interviews with parents of children who had a family pet [37, 42], the remaining studies collected data directly from participants with a companion animal. Twelve of the studies included all types of companion animals [9, 27, 31,32,33,34,35,36, 39,40,41,42] and four specifically focused on either dogs and/or cats [28,29,30, 38]. A total of 1727 pet owners were involved in the included studies.

Of the 17 included studies, 15 reported positive aspects of pet ownership for people experiencing mental health problems [9, 27,28,29,30, 32,33,34,35,36,37,38,39,40, 42] and 9 reported negative elements [9, 27, 32, 35, 36, 38, 39, 41, 42]. Neutral effects of pet ownership were reported in some of the included quantitative studies, where no difference in mental health outcomes, social contacts or loneliness were reported for pet owners compared to non-pet owners [29, 32, 35, 40]. Benefits were mostly demonstrated through qualitative data, and negative elements, which were highlighted, were largely over-shadowed by co-occurring positive impact of pets in these studies [9, 27, 32, 35, 36, 38, 42].

Themes

Emotional work - alleviating worry, providing comfort and mitigating against feelings of isolation and loneliness

Evidence from quantitative studies relating to contribution of pets to emotional work was mixed. There were significant findings for the benefits of canine companionship for military veterans with post-traumatic stress disorder (PTSD), including effects on reducing feelings of loneliness, depression, worry and irritability, and increased feelings of calmness [30] and there was some evidence for the direct effect of pets on depression and mood [30, 35] through close proximate contact and stroking [35]. However, this finding was not wholly supported by other quantitative studies, which reported neutral or small negative effects of pet ownership [29, 35, 40, 41]. A study investigating the effect of pet ownership and strength of attachment on depression found that pet owners were just as likely as non-pet owners to be depressed [33]. However this focussed on the sequela of depression not its alleviation or contribution of pets to managing post diagnosis. Interestingly, a study by Siegel found that pets had an effect in mediating the relationship between AIDS diagnosis and depression and that there was a weak trend towards dogs being more successful in this role than cats [33].

The importance of pets in relation to the provision of emotional work was a recurrent theme in the numerous qualitative studies included in the review where people reported a profound connection with their pet [9, 27, 30,31,32, 38, 39] sometimes preferring relationships with pets over relationships with other humans [37] and viewing pets as replacement family members [32]. The mechanisms through which pets made the perceived contribution to emotional work seemed to be the provision of a consistent source of comfort and affection [9, 34, 36, 41, 42]. This constant presence meant that this provision was available instantaneously without request [9, 27, 36, 42]. Pets provided calming support and were perceived to have a ‘sense’ of when it was needed.

“The dog approaches Karin when she’s crying and comforts her by lying next to her and licking away her tears. The dog hears her, and wherever he is in the house, he comes to her. We can’t always comfort her. Sometimes Karin has said, ‘It’s a good thing we have the dog, otherwise no one would be able to comfort me” [42].

Pets were able to provide unique emotional support as a result of their ability to respond to their owners in an intuitive way, especially in times of crisis and periods of active symptoms [9, 30, 31, 35, 36]. A related impact on loneliness was achieved through physical contact which reduced feelings of isolation [28, 36], providing a source of physical warmth and companionship [35], and by providing opportunities for communication [34, 36].

“It is very important of people not to feel alone and isolated, and pets help you feel like you’re like everyone else. Not less than other people. My birds are very important to me and I think other people with other pets feel that way, too” [27].

The study by Ford found that people were able to confide in their pets when they were unable to open up to other people.

“Sometimes if I talk to the cat, perhaps it's like being in a confessional, I find I can address things that perhaps I wouldn't have done normally if I hadn't have had the cat to talk to” [36].

In this respect, pets provided a safe environment where people can talk without fear of being judged or being a burden to others [9]. This was echoed in work where people reported that their dogs allowed them to express their feelings and clarify their thoughts without the concern that they will interrupt, offer criticism or advice, or betray confidence [30, 31].

“They don’t have input, “this is what you should do, or maybe you should try this” or all the other commentary I get from people, who are trying to be helpful in their own right…their dying devotion and love, it’s true friendship” [31].

The sentiment of pets being non-judgemental underpins the absence of conditionality, which was a recurring finding in included studies. Pets provided unconditional love and affection [9, 30, 31, 34, 42] which fostered self-acceptance and congruence [28]. Pets constituted a source of support which people could trust and rely on compared with other social network members [9]; they provided simple relationships free from conflict [28] and they did not overstep boundaries [31]. The latter seems to be particularly beneficial for people with Autism [37] and PTSD [30].

“The dog offers comfort in a different way to how I do, more unconditional. Åsa can hold the dog when she is feeling miserable. The dog doesn’t ask why or what’s happened” [42].

By providing unconditional positive regard, pets promoted emotional stability through the regulation of feelings, management of stress and helping people to cope with difficult life events [27, 42]. For people living alone, pets provided a source of ‘connectedness’ [27], reassurance, and normalcy [31].

She’s always there for me in a regular way of managing my stress. I tell her about my days, she snuggles, cuddles and sleeps with me [34].

Practical work - physical activity and symptom distraction

Quantitative data implicating pets in the practical work associated with mental health management pointed to the impact of dog ownership on physical activity [40] and self-reported quality of life related to physical health [29]. One study found that those with pets were more significantly likely to use ambulatory mental health care than those without [40].

Qualitative results from the studies expanded on illness specific practical work including in times of crisis [9, 28, 30,31,32, 35,36,37,38, 41, 42]. The main mechanism through which pets appeared to contribute to practical work was through the ability of pets to distract and disrupt attention from symptoms or upsetting experiences such as hearing voices, panic attacks or suicidal ideation [9, 27, 28, 30,31,32, 34, 36]. Pets contributed to practical work directly and indirectly by acting as a form of bridging tie to additional resources.

But if I’m here and I’m having…having problems with voices and that, erm, it does help me in the sense, you know, I’m not thinking about the voices, I’m just thinking of when I hear the birds singing [9].

One quantitative study by Stern and colleagues [30] demonstrated that whilst participants with PTSD did not report feeling less affected by painful memories or flashbacks they indicated that their pet tried to cheer them up when experiencing symptoms, indicating that the presence of their pet may have lessened a modicum of the negative impact of trauma [30].

Qualitative data pointed to the way in which pets were able to undertake the activities of practical work because of their consistent and proximate presence and through providing the opportunity for reciprocity [9, 27, 31, 34, 36]. Pets’ contribution to practical work is seemingly made possible through the provision of opportunities for routine tasks required to care for an animal, providing a positive focus for activity [9, 27, 30,31,32, 34, 36, 42], providing a needed challenge [36], by introducing humour into situations [9], providing a direct grounding role [30, 31, 38], lessening the negative impact of symptoms [9, 30] and reducing the stress associated with the vagaries of living with their condition [34]. One study found that participants felt that they required less medication because of this pet contribution [31].

So the physical thing of having to brush her and take her out and feed her, check that her toenails don't need cutting, you know perhaps pick up after her if she's had an accident, things like that. Cos she can be quite demanding as you've seen, she's up and she wants attention all the time, so it… interrupts your thought process a lot of the time [36].

They are something that is very important in my recovery and helping me not get too depressed. Even when I was so depressed, I was kind of suicidal. I never got really bad, but I was suicidal at one time. The thing that made me stop was wondering what the rabbits would do. That was the first thing I thought of and I thought, oh yeah, I can’t leave because the rabbits need me. So they were playing a really big role in that [32].

Pets could contribute to a sense of preparedness to take self-management action through increasing people’s positivity and self-efficacy [32, 34, 41, 42]. They encouraged their owners to stay in the present avoiding worry and ruminations about past behaviours [28, 30] or concerns about the future [34]. Pets were also considered important in terms of providing protection for their owners [28, 31]. This was particularly of value for those participants experiencing the constant vigilance associated with Post Traumatic Stress Disorder [31].

He’ll start nudging me or hopping on me to get me into a petting session or he’ll grab my pants leg and start pulling on me or like my shirt or my arm and start pulling on me to kind of like bring me out of a flashback or anything else like that [31].

Owners felt that their pets could sense when practical support for mental health was required and acted accordingly [9, 28, 31, 42]. However, this was not universal to all studies indicating the impact of pets cannot be fully explained by this behavioural initiation [37].

The puppy followed Bengt’s mood from the very first day. The dog reads him inside and out, she knows exactly when to go to him and when to keep back. If Bengt is unsettled and moving around, he may stop occasionally and sit down … and then along she comes. Then she kneels down and starts to nudge and lick him, and he starts to stroke her. She also knows if he’s in conflict with us. Then she follows him … and if he hasn’t closed his door, she goes in and sits with him [42].

Pam named the contact itself as playing a significant role in helping her to manage anxiety attacks. She specifically described an example of when her companion dog came to her during an anxiety attack in the middle of the night: Brutus licked her face and laid next to her for the rest of the night, and contact with him immediately improved her acute symptoms [28].

Indirectly, pets encouraged a form of behavioural activation. Pets were seen to enhance mobility [41], increase exercise [30, 35, 36, 40] and promote contact with nature [30, 36] all of which were considered beneficial to mental health.

Pets as conduits to social interaction and emotional nourishment

A feature of the role attributed to pets in terms of mental health management in the qualitative data was the various ways in which they facilitated the quality and quantity of social interactions. Pets reportedly increased social interaction with others including friends and family [34] and with more peripheral social interactions [9, 38]. They also fostered a sense of social and community integration [9, 32, 35, 36, 38, 42]. Interestingly, one study found that dogs increased social interactions that would not have been possible without their pet (e.g. other dog walkers [36]). This was supported by some [39] but not all of the included quantitative studies [29, 32, 39, 40] indicating a complicated relationship between pets and social interaction which may be mediated by type of pet and/or number of pets [22].

Get out of the scope of a physical disability. I mean a physical disability yeah. I can’t get through that door. I can’t get up those steps. For a mental health patient it is not the physical barrier it’s an invisible [barrier] … Yes, these guys help me interact. Butch, when we go out … when Butch and I go out, we interact because he gets so much attention and with the attention focused on him, I can get engaged in all sorts of conversations with people who like dogs, so with these guys we develop friends who are into the same thing [38].

That surprised me, you know, the amount of people that stop and talk to him, and that, yeah, it cheers me up with him. I haven’t got much in my life, but he’s quite good, yeah [9].

The reasons identified in the included studies as to why pets were considered useful in terms of enhancing the amount and quality of social interactions included having the confidence to venture into new social situations with their pet, owners finding it easier to be in the presence of other people when their pet was present [30], being more open during social interactions [28] and being able to have difficult conversations with existing friends and family through their pet [34, 36].

Biographical work - identity, a sense of self-worth and existential meaning

The data implicating pets in biographical work was mostly derived from the qualitative data. Two quantitative studies addressed this type of work; one found that despite a low effect score, pet owners performed significantly higher than non-pet owners on meaningful activity scales [39] and another found that since getting their pets individuals felt better about themselves as people [30].

Qualitative data suggested that pets provided their owners with a sense of purpose and gave meaning to their lives [41]. Often participants described how this had been diminished since diagnosis with a mental health condition but that pets helped them to overcome this and provided them with a platform for going forward with their lives [9, 38]. This sense of meaning and purpose included pets giving their owners a reason to live [9, 32], to contributing to a sense of control and empowerment [9, 31, 32, 35] and giving individuals hope for the future [9, 31]. This was considered particularly important when people were feeling consumed by illness or when self-management felt out of control [32].

It gives me something to do, to take care of them, the cleaning of the cage, feeding them [34].

Owners’ felt that their pets contributed directly to maintaining a consistent sense of identity and self [9, 27, 32, 36, 39, 41]. They felt pets provided a form of validation through the pride associated with successfully caring for a pet [9, 28] but also as sustaining elements of pre-illness identities including roles of mother, pet owner or animal lover [9, 36] and as being a protector of animals [28, 31].

My best quality is that I love animals and I take care of animals… Other than that, I can’t think of anything real outstanding [32].

Pets were also considered relevant in terms of mediating how other people viewed them [9, 42]. Pet ownership connected their owners to valued activities such as hobbies [35] and were considered a culturally sanctioned meaningful occupational and social role [38, 39]. One study also indicated that the mastery achieved through the training of animals also contributed to a positive sense of self [9].

Participants described elements of relationships with pets that were important to their mental health including the nature of relationships as simple and reciprocal, pets as understanding and honouring personal boundaries and pets not holding past behaviours against them [9, 27, 32, 36, 39, 41]. These components were often missing from other human relationship and were considered important aspects of the human/pet dyad [9].

For Irene, taking care of her companion dog facilitated a change in her sense of self, from seeing herself as someone who “destroyed anything [she] loved” to seeing herself as a loving, nurturing protector [28].

There’s a lot less things to worry about. I mean you can’t…you can’t like be like if he was naughty or anything like that you’d tell him off and that was it and there’d be no hard feelings. That there’s not, you don’t get the nastiness [9].

Pets impacted directly on the management of negative perceptions and experiences related to a diagnosis of mental illness which arose either from themselves or from others within and outside of their existing social networks [9, 28, 31, 34, 35, 39]. The mechanisms through which this appeared to operate included counterbalancing a loss of social status as a result of being diagnosed with a mental illness, providing non-judgemental acceptance often not available elsewhere [9], making owners feel wanted and valued [34, 39] and encouraging owners to feel good about themselves [28, 30]. One study proposed that companion animals symbolised abused childhood selves and that by caring for a pet they may have symbolically been caring for this part of themselves [28].

When he comes and sits up beside you on a night, it’s different, you know, it’s just, like, he needs me as much as I need him, sort of thing [9].

Negative aspects of pet ownership

Despite an overall sense of the positive impact of pet ownership on the management of diagnosed mental health disorders, some negative aspects surfaced within individual quantitative and qualitative studies. This included aspects such as financial costs and housing situations, the burden of pet ownership especially if pets were unruly which could be detrimental to mental health and the guilt that owners experienced if this was not managed successfully [9, 35, 36, 38, 39]. Horses and dogs were considered the most burdensome in this regard and research highlighted the importance of matching pets to individual circumstances [36]. The early stages of pet ownership were often the most difficult for people but were concomitantly considered as an important investment in terms of future support and companionship [35]. Pets could also be seen as a barrier to aspirational goals associated with recovery such as travel [9, 35].

When I was working it wasn't a problem, but obviously when you're on a low budget income, it does become a financial hazard, because they're just unexpected you know. That's where the issues become, do you keep them or do you…and you don't want to let them go so you're sitting there, having to cut back and scrape the bottom of the barrel to make sure they're looked after sort of thing [36].

I was trying to care for 3 cats of my own that I loved, stray cats in the neighbourhood I was feeding. I tried to spay the ones that appeared to be pregnant, and I was putting food out twice a day, and I was just feeling overwhelmed, just overwhelmed and more and more depressed, more a sense of failure, and finally it just got worse and worse and worse [32].

The potential or actual loss of beloved companion animals was a major source of distress for owners [9, 32, 38, 42] but it was acknowledged that joy could still be taken in their memories once death had been come to terms with [32] and that such experiences could facilitate understanding of other difficult life events [42].

I was very depressed by [pet’s] death. While she was getting worse, we had her home for a while and I had to make myself be strong […] It was more after her death that I kind of broke down, and just thinking about her would make me cry for a couple of weeks or more. Gradually I got to the point where I knew that it was her time. The life that she had and what she had given to me, I could always think of that. It always makes me happy [32].

Participants described how other people including health professionals were often concerned about the safety of their pets and their ability to care for them [27, 33]. Siegel et al. demonstrated that those with HIV felt there was a perception that they should not have pets as a result of their condition [30]. This may also apply to those with mental health conditions but this was not covered in any of the included papers.