Actually, there is absolutely NO evidence that depression is caused by an imbalance of chemicals, that is a myth. Depression is caused by nutritional deficiencies and/or lack of physical activity (as most diseases are) or by an event that happened in that person's life. If it's the former, then all it is, is a natural human emotion. Or perhaps they're being exposed to too much electromagnetic fields (Wi-Fi, television, cpu's, laptops, etc.) And 97% of people die within five years of taking chemotherapy... you can take that for what it's worth. If someone is depressed, it's very likely that they also don't exercise/get outside a lot and have an absolutely terrible diet.