Here is what to expect and to watch for when starting an antidepressant:
1) some people will have an immediate positive effect from an antidepressant, they will notice improvement in mood or anxiety right away.
2) most people, though, will notice very gradual improvement, and it will require at least two weeks at a full dose to have a substantial change in symptoms. Some people may require a longer period of time, up to 2 or 3 months or longer, to notice a benefit.
3) many people have their worst side-effect problems in the first 1-2 weeks of starting an antidepressant. Side effects might include sleep problems, nausea, sweating, or increased anxiety (there can be many more side-effects too). Usually these side effects settle down after 1-2 weeks.
To reduce the likelihood of this being a problem, I usually start most people on a tiny dose of an antidepressant (for example, 1/4 tablet daily), to allow people to adjust more gradually. The advantage of this is less side-effects, but the disadvantage is that it could take longer to experience a benefit. Studies show that the most significant and consistent positive effects of antidepressants begin at a full daily dose (usually one tablet daily of most antidepressants).
4) Some people may have severe side-effect problems. If this happens, I usually recommend that they discontinue the medication, so that we can make a new plan. People who have bipolar disorder, or who may have a higher risk (e.g. through family history) of developing bipolar disorder, have a higher risk of severe side-effects from antidepressants, and have a higher risk of experiencing a manic episode as a result of taking an antidepressant.
5) In all cases, I like to see and hear from people frequently whenever a new medication is started, so that any possible problems can be addressed early. Sometimes side-effects can quietly pass, other times it might be best to back off, stop the medication, and try something else.
6) The benefits of antidepressants can sometimes be subjectively obvious, other times they may be quite subtle. Others around you may notice beneficial effects before you do yourself. It may be only after a few months that you can look back and see (and feel) that things are better.
7) There is evidence that antidepressants reduce the risk of relapse in recurrent depression (probably about a 50% reduction). For some people, even if they may not need the antidepressant to treat current, acute symptoms, they may benefit from continuing the medication so as to prevent relapse. Of note, studies also show that psychotherapy (CBT in particular) reduces relapse rate by about 50% as well in recurrent depression. And there is evidence that the combination of medication + psychotherapy is synergistic, and may reduce the relapse rate by 75%. Reference:http://garthkroeker.blogspot.com/2009/03/long-term-antidepressant-therapy-to.html
8) Sometimes you need to try several (or many) different antidepressants, before finding the one that suits you best. Different medications in the same class (e.g. the various different SSRI's) can sometimes "suit" people quite differently. For many of my patients, a combination of two antidepressants, or sometimes more complex combinations of other medications, ends up helping best. In these situations, I do think it is important to give each medication trial a good, thorough try (usually at least two months) before making major changes.