Demographic characteristics

From June to October 2021, 573 patients with depression attended both psychiatric outpatient clinics, and 566 of them agreed to participate and complete the questionnaires. The response rate was 98.8%. The mean age was 43.8 ± 18.1 years. The majority of participants were female (75.4%), Buddhist (73.7%), unmarried (56.5%), and had no history of physical illness and substance uses (56.2%, 91.7%, respectively) (Table 1). The most common physical illnesses were hypertension (31.3%), dyslipidemia (29.6%), and allergy (23.9%). The substances used by the participants were tobacco (3.4%), cannabis (1.1%), and amphetamine (0.5%). No statistically significant difference in demographic data was detected between the participants, according to the two hospitals.

Table 1 Demographic characteristics (n = 566)Depressive symptom profiles

In regard to depressive symptoms, the majority of participants identified core symptoms, at the initial phase of depression, that had high frequency, and high impact on patients’ daily lives and they expected that antidepressants would relieve them. These symptoms were: sleeping problems, feeling depressed or hopeless, and loss of pleasure or interest in operating things (Table 2, Fig. 1).

Table 2 Core depressive symptoms, symptom impact on daily life and symptoms that are expected to be relieved (more than 1 answer) (n = 566)Fig. 1

Prevalence of depressive symptoms and symptoms that impact daily life at the initial phase of the first episode of depression (n = 566)

In regard to age, there was a statistically significant difference in depressive symptoms at the initial phase of illness between different age groups (p < 0.001). The most common depressive symptoms among young adults were thoughts of being better off dead or of hurting themselves (38.7%), moving or speaking too slowly (37.9%), feeling bad about themselves or failure (34%), trouble concentrating on things, and a diminished ability to think (32.1%), while the main depressive symptoms among the elderly were sleeping problems (24.6%), restlessness (24.2%), and a loss of interest or pleasure (23.2%) (Fig. 2).

Fig. 2

Depressive symptoms at the initial phase of the first episode of depression as per age group (n = 566)

Residual depressive symptoms

Of all participants, 257 (45.4%) reported having a PHQ-9 score of nine or greater, indicating the presence of residual depressive symptoms (Table 1). Moreover, 55 (9.7%) participants were still being severely depressed (Fig. 3).

Fig. 3

Depression according to PHQ-9 (n = 566)

The most common residual depressive symptoms were sleeping problems (71.2%), low mood (62.6%), loss of interest or pleasure (62.3%), and poor appetite (61.9%). In regard to age groups, the most common residual depressive symptoms among young adults were thoughts of hurting themselves or suicidal ideation (65%), trouble in concentration (54.7%), feeling bad or low self-esteem (53.8%), and loss of interest (53.5%), while the main residual depressive symptoms among the elderly were low mood (10%), and sleeping problems (9.9%) (Fig. 4). Furthermore, 44 (17.1%) participants had three residual depressive symptoms, and 8.6% to 12.1% of participants had more than three residual depressive symptoms (Fig. 5).

Fig. 4

Frequency of residual depressive symptoms as per age group (n = 257)

Fig. 5

Number of residual depressive symptoms (n = 257)

Treatment profile

One hundred and thirty-seven (24.2%) participants received antidepressants for less than one year, and half of them received antidepressants for more than 2 years (Table 3). The median duration of receiving antidepressants was 26.9 months (IQR = 12.0, 62.9).

Table 3 Demographic characteristic and treatment categorized by PHQ-9 score

Out of all participants, 372 (65.7%) and 162 (28.6%) received one and two types of antidepressants, respectively. The most prescribed antidepressants were selective serotonin reuptake inhibitors (SSRIs) (51.1%); sertraline (27.9%); fluoxetine (15%), and SSRIs plus other antidepressants (13.9%) (Table 4).

Table 4 Type of antidepressants that the patients received (n = 566)The association between demographic characteristics, treatment profiles and residual depressive symptoms

Variables whose p-values from the univariate analysis were lower than 0.2 were included in the initial model for multivariate analysis. Multivariate analysis indicated that age, religion, education, and physical illness were statistically significant factors associated with having residual depressive symptoms. The patients with depression aged between 18 to 24, had a higher rate of residual depressive symptoms than the older group, the adjusted odds ratio (AOR) was 12.08, 95% confidence interval (CI) at 6.28 to 23.23. The same was true when comparing them with those whose religion was Islam or Christianity, had higher education, and physical illness; AOR (95% CI) was 1.70 (1.10, 2.62), 1.73 (1.16, 2.57), and 1.55 (1.02, 2.35), respectively (Table 5).

Table 5 Factors associated with residual depressive symptomsDiscussion

This study indicated that the most common depressive symptoms and symptoms that have a strong impact on a patient's daily life were sleeping problems, feeling depressed or hopeless, and the loss of pleasure in doing things. There was a statistically significant difference in common depressive symptoms between age groups. Selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), mirtazapine, bupropion, and agomelatine being first-line recommendations for pharmacotherapy for MDD [15, 22]. Furthermore, the most common antidepressant prescription by our psychiatrists was SSRIs (51.1%). Notably, 45.4% of participants reported having residual depressive symptoms (PHQ-9 ≥ 9). The most common residual depressive symptoms were sleep problems (71.2%), feeling depressed (62.6%), loss of pleasure (62.3%), and poor appetite (61.9%). Moreover, the associated factors relating to residual depressive symptoms were younger age, high education level, and having physical illness.

In regard to depressive symptoms profiles, in this study, we found that sleeping problems, feeling depressed or hopeless, and loss of interest or pleasure were the symptoms presenting with the highest frequency and level of impact on the patients’ daily lives. The depressive symptom profiles from our study feature a number of differences versus a study from Canada [22] which identified that fatigue, poor concentration or diminished ability to think, loss of interest or pleasure, low mood, and feeling worthlessness or guilt were the symptoms with the highest frequency and level of impact on patients’ daily lives. A potential explanation for these discrepancies may be due to different study instruments, population ethnicity, age group, and cultures. However, our study reported a statistically significant difference in depressive symptoms between young adults, adults, and elderly age groups. These results were similar to a prior study that identified symptom differences among young adults, adults, and elderly patients with depression. In regard to young adults, the previous study found that physical or vegetative disturbances (changes in appetite, weight, loss of energy and sleep changes) were common. Moreover, a vegetative symptom profile was only seen in young adults with depression. In regard to adults, concentration difficulties, and anhedonia/loss of interest were more common. [23]. Therefore, before prescription, physicians should consider the core depressive symptoms which should be particularly targeted; and that this may vary due to age group symptom related differences.

Considering residual depressive symptoms, almost half of the participants (45.4%) reported residual depressive symptoms which included sleeping problems, feeling down, loss of pleasure, and poor appetite. Additionally, this study identified that the mean duration of receiving antidepressants was at 26.9 months, and that 65.7% of participants received one type of antidepressant, and that SSRIs were the most common antidepressants prescribed. In regard to the neurotransmitter model of function in depression, a well-known concept, depression is described as a combination of two components: a lack of positive affect and an increase in negative affect. Negative affect means viewing the world as an unpleasant, disturbing, hostile, and threatening place. Lack of positive affect equals an inability to take pleasure rewards from normal activities. During treatment with antidepressant medication, some patients might experience particularly unresponsive depression-related symptoms with a higher lack of positive affect, while other patients might experience depression with an increase of negative affect, such as symptoms of anxiety [24]. As per a prior study, clinical trials of antidepressants have shown that some dual-acting antidepressants, such as serotonin–norepinephrine reuptake inhibitors, may result in higher rates of remission than other pharmacological agents, and with fewer residual depressive symptoms than treatment with only SSRIs [16]. Based on recent information from studies about antidepressants, it might be possible to assign specific symptoms of depression to specific neurochemical mechanisms. Norepinephrine may be related to energy and alertness as well as attention, interest in life, and anxiety; serotonin to obsessions, and compulsion, anxiety; and dopamine to having an interest in life, pleasure and reward, as well as motivation. Increasing any of these three neurotransmitters could elevate mood, but the other elements of depression may be particularly responsive to a specific neurotransmitter [25]. Therefore, the different neurotransmitters may regulate different brain functions in patients with depression; different antidepressants due to their dissimilar pharmacology target a diversity of neurotransmitters, and these may affect different symptoms of depression. Knowing which particular neurotransmitters are related with what symptoms of MDD may help physicians prescribe pharmacological agents that target specific mechanisms that in turn target specific depressive symptoms [26, 27]. In this study, most participants received one class of antidepressant, SSRIs, and this may be the reason for the lower rates of remission versus treatment with multi-acting antidepressants. In addition, the most common residual depressive symptoms were sleeping problems, loss of pleasure, and poor appetite; and it might be possible that these specific symptoms of depression did not respond as well to SSRIs. It is recommended that physicians should be concerned by the individual variability of symptoms and ensure that selecting antidepressants targets core depressive symptoms in a specific manner. Additionally, sleeping problems may be a comorbid disease, such as insomnia disorder [28]. Therefore, monitoring residual depressive symptoms in the remission phase may be necessary.

In this study, patients with depression, aged 18 to 24, had a higher rate of residual depressive symptoms than the older group, the AOR was 12.08. Based on prior studies, depression was a prevalent and serious mental disorder among youth adults or adolescents and adults, and it was related with suicide, an increase in family problems, substance abuse, absenteeism [29], and disability that could be lowered to perform life activities associated to work performance and/or academic achievement including a decrease in student grade point average (GPA) [24]. Furthermore, the pattern of increasing interference of depressive symptoms with academic performance, might peak during the month of diagnosis and decrease afterward, with the lowest levels reported four to six months post-diagnosis [30]. Thus, antidepressants that specifically target the depressive symptom of youth-adult patients should be prescribed rapidly and effectively.

Additionally, this study identified that patients with higher education and experiencing a physical illness had a higher rate of residual depressive symptoms than the rest of the group. Higher levels of education could be associated with them having a higher level of work responsibilities and as a result more tension. While having physical illness may be associated with elevated life stress. Some physical symptoms could also produce anxiety, distress, suffering, and sleeping problems. Therefore, these factors may make depression more complicated.

Finally, several other factors that were not addressed by our study could have possibly influenced the response to treatment and the presence of residual depressive symptoms, such as alcohol usage, and biological factors; an imbalance of pteridine metabolism in depression [31]. The prior study reported increased levels of markers of inflammation and oxidative stress in MDD. Moreover, likewise poorer antidepressant treatment response was related to higher baseline levels of the major oxidative stress marker, F2-isoprostanes, in vivo [32]. However, when treating patients with depression in clinical settings, physicians should deliberately select an antidepressant based on the specific presenting and individual symptom profiles of the patient. Selecting the appropriate antidepressant for a patient’s particular symptoms might offer the best chance for a successful response to treatment [25, 26]. Furthermore, the importance of shared decision-making, drug efficacy, side effects, medical treatment rights, covered medical expenses, and economic status should also be taken into consideration. Therefore, psychiatric training and national mental health care policy should be concerned with the desire for treatment of depression related to high individual variability.

This study had both limitations and strengths worth mentioning. To our knowledge, this is the only study on this topic conducted in southern Thailand during the last decade. However, this study had some limitations as it was a cross-sectional survey and utilized self-administered questionnaires; therefore, some misunderstandings about the intended meaning of the questions may have taken place. Another drawback is that our data were quantitative, the sample size and that the participants were restricted to patients with depression in lower, southern Thailand. Most participants were female in gender and had a high educational level. Hence, these results may not demonstrate the situation or condition of patients with depression in all gender groups, all educational levels, or the whole country in a proportionate manner. It is recommended that future studies feature a larger number of patients with depression from other hospitals in Thailand; and that a more comprehensive, multi-centered research study, with more qualitative or in-depth methods should be employed. Moreover, there are some factors to be aware of, such as alcohol usage or abuse, medication adherence, drug tolerability, psychotherapy, family, and social support, as these may influence the prognosis or the outcome of treatment among patients with depression.