In many cases, a single form of therapy does not relieve symptoms of depression or anxiety. For every person, I recommend a range of healthy lifestyle changes, and I usually would encourage psychotherapy. For many, I encourage trials of antidepressant medication as well. For a significant number of people, a single medication does not relieve symptoms. In these cases of treatment-resistance, it can help to search for an effective combination of several medications. In this post, I will discuss the evidence-based foundation for combining antidepressants.
I find that several different antidepressant combos are worth trying, including an SSRI + mirtazapine, venlafaxine + mirtazapine, or an SSRI + bupropion. Adding trazodone to another antidepressant can be helpful for sleep, although I am less convinced of this combination substantially improving depressive symptoms. Combining newer antidepressants with older tricyclics is another area of interest, which I think we should be open-minded about, but I don't tend to prescribe tricyclics very often, mainly due to concerns about safety and side-effects. There are far fewer careful studies of antidepressant combinations compared to studies looking at single medication treatments, so the level of evidence in this area is not very strong yet. But here are a few references to existing articles from the research literature (I will try to expand my list over time):
This is a 2009 article from a Montreal group (Blier et al.) showing that a combination of mirtazapine + SSRI (paroxetine) led to significantly more improvement in depressive symptoms over 6 weeks, compared to groups taking either medication alone. The combination was well-tolerated for the most part-- in particular there was little difference in side effects experienced by the combination group compared to the group taking mirtazapine alone. Unfortunately, there are conflict-of-interest problems here: the study was funded by Organon, the mirtazapine manufacturer. And several authors of the study were "consultants" paid by the drug manufacturers for speaking engagements. The continued behaviour of psychiatrists accepting corporate money to give "educational lectures" is unfortunate. Usually large sums of money are involved. Please see my posts on industry-sponsored research: http://garthkroeker.blogspot.com/2008/11/biases-associated-with-industry-funded.html and http://garthkroeker.blogspot.com/2009/05/my-experiences-with-industry.html
Here's another recent article (2010) by Blier et al, again making a strong case for using combination antidepressants right from treatment initiation: http://www.ncbi.nlm.nih.gov/pubmed/20008946
This is an open study looking at combining escitalopram (Cipralex) with bupropion in chronic depression. There was no placebo or comparison group, so the study has a weak design. But it shows the combination was quite well-tolerated, and led to 50-60% of patients experiencing a remission of symptoms after 12 weeks, which in general is a better result than most single-agent trials, especially in chronic depression. The study was funded by NIMH, which reduces the likelihood of bias.
This is a 2006 review from Biological Psychiatry looking at combinations of bupropion with SSRIs. It is a good paper, but really most of the evidence presented is of mediocre quality. It does support the idea of using bupropion-SSRI combos, to improve treatment response in depression, and also to reduce SSRI-induced sexual side-effects such as delayed or inhibited orgasm.
This interesting 2004 paper is looking at the treatment of patients with depression plus chronic headache, using citalopram alone, or amitriptyline (a tricyclic antidepressant) alone, for 16 weeks. Then, a combination of the two medications was given to non-responders, for a further 16 weeks. The combination group showed substantial improvement in both headache and depression.
This is an important 2004 study from Biological Psychiatry showing that 6 weeks of a fluoxetine (SSRI) + desipramine (tricyclic) combination was more effective than either drug alone, in treating depressed patients admitted to hospital. While similar proportions (about 35-50%) of patients failed to respond to any of the three treatments, those patients who did respond improved much more with the combination. That is, the combination treatment led to a significantly higher chance of total remission compared to either single antidepressant treatment. The study was funded by NIMH.
This 2002 study looked at several options to treat non-responding depressed patients taking fluoxetine: the first group took a higher dose of fluoxetine (40-60 mg/d), the second group took a combination of regular-dose fluoxetine + desipramine, and the third group took fluoxetine + lithium. The results favoured the first strategy, of maximizing the dose of fluoxetine, instead of combining with something else. However, this result is not very useful, since normally we would maximize the dose of a single agent first anyway, before resorting to a combination. Yet the study does show that combining is not necessarily the best first step in addressing treatment-resistance. It was funded by NIMH.
This is one of the few studies looking at trazodone combinations: in this case, trazodone+fluoxetine showed some promise in treating resistant depression.
A weak old study from 1992 showing that trazodone can sometimes help as a combination with an SSRI (in this case, fluoxetine). 3 out of 8 depressed patients in this study improved with the combination (of course, this means that 5 out of 8 did not improve).
This is a 2009 review article on combining antidepressants. It is in German, which makes it hard for me to read!