text: The least amount of time, would always be better. It would generally depend on the Physciatrist perscribing them. If you are referring to how long it takes to be effective, most take 6-8 weeks to get to a therapeutic level on the average...some take longer or quicker depending on the type and the person. Remember that antidepressants don't cure anything...they are a supplement to take, while you are working on your issues. You can actually improve chemical brain functioning by positive thinking!