Effexor, or venlafaxine, is an anti-depressant medication used to treat depression and anxiety. Several classes of medications are used to treat these conditions. If venlafaxine doesn't lead to improvement, other medications can be tried. Different people respond differently to the same medication, and much of the treatment with antidepressants is done on a trial and error basis. Each class of medications has a different side effect profile, and these help determine which medication can be tried.
Tricyclic antidepressants, or TCAs, are a class that includes amitriptyline, imipramine and nortriptyline. TCAs used to be used more widely; they have fallen somewhat out of favor due to their relatively high incidence of side effects, which include drowsiness, EKG changes, dry mouth and blurry vision. They are, however, no less effective than newer medications. According to MedlinePlus, TCAs should, in general, be avoided in patients with heart disease. Caution is required when using them to treat people who have a variety of other medical conditions, including glaucoma, seizures and an enlarged prostate. As with all antidepressants, TCAs carry an FDA warning about an increase in suicidal thoughts and suicide attempts when treatment is started.
Serotonin specific re-uptake inhibitors, or SSRIs, include medications such as citalopram, fluoxetine and paroxetine. They are used to treat depression and anxiety disorders. As an article in "JAMA" explains, SSRIs can be used in place of venlafaxine. For example, when one SSRI has failed to cause significant improvement, changing to another SSRI is as effective as switching to venlafaxine, and causes fewer side effects.
Side effects of SSRIs include increased suicidality, nausea, sexual dysfunction and agitation. As "Kaplan and Sadock's Comprehensive Textbook of Psychiatry" explains, SSRIs can also cause low blood sodium, which can lead to confusion, seizures and a decreased level of consciousness.
Mirtazapine is a unique antidepressant, most often used in patients who have trouble sleeping and eating as a result of their depression. As an article in "American Family Physician" notes, it's also useful in people who have a significant component of anxiety along with their depression. Its side effects include drowsiness and increased appetite, side effects which are beneficial to these patients. Decreased production of white blood cells is a rare side effect that can lead to an increased risk of developing infections.