Depression is a condition that has been in existence for quite some time now. Even the ordinary person knows what depression is despite lacking any medical background. While depression might be a commonly known condition, similar to the common cold, the field of science has not been able to understand pathogenesis and pathophysiology of depression in full. The medical community has put a lot of efforts in the research with the aim of demystifying the condition that affects a significantly large percentage of the population cutting across all age groups. This study has been able to provide useful information regarding the causes of depression and addressed the issue of effective treatment. This paper highlights the new theories about depression that have been developed, the impact of the research on treatment strategies currently in practice and who it affects in today’s society.To begin with, what exactly is depression? Depression is defined as the point or points in an individual’s lifetime when they are mentally unstable and factors that can easily correlate to depression is by sadness, discouragement, and loss that can occur as early as the teenage years. In addition, depression causes changes in behavior, perception and especially changes in ones everyday life. Dr. David Kalkstein, psychiatrist at Penn Foundation stated that “Depression amongst teens generally starts when a child hits puberty, but could possibly begin the day they were born if chemically imbalanced”. On the other hand, depression can pretty much affect anyone at anytime anywhere. Teens, children, and adults are all affected in both different and similar ways where one might not even notice symptoms. Through findings, depression is experienced mostly by teens even though it is mistakenly classified as a type of ‘adult illness’ or hormone changes in which they experience fluctuating mood swings. “Twenty percent of high school students are deeply unhappy or have some kind of psychiatric problem”. The causes for depression in teens are sometimes more harsh than the causes in adults especially in today’s society and will most likely exacerbate in the future due to the amount of exposure kids are shown nowadays. In a teen’s lifetime they have to face many problems and in some cases, face these problems more than once usually without the reach of a professional adult. Teens have to deal with peer pressure problems at school, problems at home, the deaths of loved ones, and if they are already using drugs, this could also be a cause but these factors can certainly affect adults and elders too. Many teens and even adults also have to deal with the point in their life when they wonder if they are attractive or attracted to other people, of the opposite sex, same sex etc. For example, if they do believe that they are unattractive, they will most likely feel as though they have failed at something and this can lead to a form of depression such as anxiety where they begin to overthink situations. Depression also comes after a teenager is trying to learn about himself or herself and understand their body, and their emotions towards others.As stated previously, the cause of this condition has for a long time been considered to be a chemical imbalance in the brain as a result of excess or inadequate presence of neurotransmitters, but this is changing as other complementary causes have been identified. Recent research has revealed that the lack of regeneration of nerve cells is a viable explanation for depression. Evidently, the hippocampus in a depressed subject is relatively smaller that of a subject that is not depressed. This finding points to an existing relationship between slow production of new nerve cells and low moods. Scientists are exploring the possibility of this being an analogous cause of depression. Antidepressants used for the standard treatment of depression often take weeks before the patient begins to feel better. It has been argued that if depression were merely a problem of chemical imbalance, then the antidepressants would be active within days because they increase neurotransmitters in the brain. Although the necessary chemical conditions may be re-established, it takes time for the brain to produce new cell in the hippocampus is the explanation that offers support for this new theory. The chemical imbalance may be a cause of depression but undoubtedly not the only one. An emotional disorder is often the basis for conceptualizing depression and the treatment strategies, but this has been challenged primarily because of the nature of results achieved from treatments developed from this line of thought. Future research in developing a therapy for depression should consider depression as an infectious disease. Research should be focused on parasitic, bacterial or viral roles in the etiology of this disorder. There are three primary arguments to support this idea. Firstly, affective symptoms such as loss of energy are used in diagnosing depression in patients although inflammatory biomarkers of the disorder suggest an illness related origin. Currently, no evidence can be provided to support this argument, but since it is a feasible idea, it warrants further research. Secondly, existing research provides clear evidence that emotional behavior may be affected by a bacterial, parasitic or viral presence in the human body. Finally, micro-organisms that are hosted in the human body have their genetic makeup that is continually changing as it is passed across generations which elicits further research into the genetic background of the illness. The use of infectious disease protocols for research may be a strategy worth exploring in explaining the causal roles of various factors concerning depression and development of more effective treatments.Antidepressant medications prescribed for depressed patients at times do not work for all patients and have adverse side effects for most users, thereby, forcing medical practitioners to re-assess the therapies and drugs used for treatment. Research carried out by the National Institute of Mental Health (NIMH) showed that out of three patients, only two would fully recover on antidepressant medication. Efforts to help partially unresponsive patients that do not recover have resulted in the extensive use of augmenting agents with antidepressant medications. For example, prescribing typical psychotic drugs to a patient using antidepressants will significantly increase its effectiveness. The good results yielded from augmentation of antidepressants have made it a common practice in depression treatment. Research has also been focused on producing alternative drugs with lesser side effects resulting in the recently approved drugs which have a similar mechanism of action to existing selective serotonin reuptake inhibitors and serotonin-norepinephrine reuptake inhibitors. Recently approved drugs have helped medical practitioners in the psychiatric field to find much easier the right medication fit for a patient, which was usually problematic with patients being unable to withstand the adverse side effects of most antidepressants. The new drugs and augmentation of antidepressants have marked a new era for depression treatment with better patient tolerance for drugs and increased effectiveness of treatments. The fraction of patients suffering from depression that is unable to recover from treatment with existing drugs has pushed for the development of a new version of antidepressants that have a different mechanism of action. The earliest types of depression medication were the monoamine oxidase inhibitors and tricyclic antidepressants. These were later replaced by the selective serotonin reuptake inhibitors and serotonin-norepinephrine reuptake inhibitors. All depression medication, from the 1960s until now, is focused on three neurotransmitters: serotonin, norepinephrine, and dopamine. To help patients who are unresponsive to the existing drugs, a new type of drug focused on the glutamatergic neurotransmitter system is being developed. Although the idea of using alternative drugs focused on glutamate neurotransmitter system is not new, having been suggested by John Krystal in the 1990s who noted the effect of ketamine on depression, intensive research on the medication began recently. Research on ketamine consequently resulted in research on other drugs that have similar pharmaceutical properties. Alternative modes of administration are also being tested such as the efficacy of intra-nasally administered medications. Antidepressants with a new mechanism of action will provide a lasting solution to many patients who have been unresponsive to all existing drug and augmentation therapies.There have also been remarkable developments in behavioral therapy in the recent years. Behavioral therapy is a form of clinical psychotherapy that focuses on behavior change. The most efficient and widely used behavioral therapy is cognitive behavioral therapy (CBT). CBT differs from the other forms of depression therapy in that it focuses on cognitive restructuring based on the present – what and how one thinks rather than why one thinks that way. CBT also stands out in that it has a specified time limit which is fifteen weeks. This therapy uses an educational approach that is made up of structured learning experiences to teach the patient to monitor his or her behavior. There are also other types of therapy that can be used to manage depression as an alternative to CBT. Developments in behavioral therapy have significantly improved its success rate in handling depression from the clinical psychotherapy approach.