Friday, February 19, 2016

Do Higher Doses of Antidepressants Work Better?

It is common practice in psychiatry to increase the dose of an antidepressant if the standard dose is not helping enough.  Sometimes doses are increased before even finding out if the lower dose is working. 

But it is interesting to consider evidence that higher doses actually do not necessarily work better:

Ruhé et al. (2009-2010) have published research on this issue, and conclude that SSRI dose increases do not improve effectiveness.  Their explanation for this is quite simple:  serotonin receptors are already well-occupied at standard doses, and this does not change with dose increases:

In general, it is indeed interesting to see scanty evidence that increasing antidepressant doses lead to improved effectiveness, even for treatment-resistant cases.  

This issue came to my attention upon reading Lam's recent article about using light therapy to treat non-seasonal depression   (  Their medication groups used only 20 mg of fluoxetine, without the possibility of increasing the dose.  They cited some old, dated references to support this, such as Altamura et al (1988), and  Beasley (1990): 
A better, more recent article reviewing antidepressant dose vs effectiveness is by Berney (2006):

In many studies, higher doses may appear to work better, mainly because the dose was increased before the lower dose had a chance to work fully.   The lower dose may well have worked just as well as the higher dose.  Controlled studies comparing different doses do not support the belief that higher doses work better.

So it should not be routine practice to increase antidepressant doses beyond a standard "full dose" which is usually one tablet or capsule daily.    In many cases, the different dosage regimes are likely to be equivalent.  It is relevant to consider that higher doses mainly benefit the pharmaceutical companies, since they are selling more product despite the effectiveness being the same.  Therefore, presentations of research data about antidepressant effectiveness may be biased in favour of higher doses.  An extremely common research design in antidepressant studies is to have "flexible dosing," usually leading to the antidepressant group averaging about twice the standard dose in the end.  This design, even when treatment effects are shown, biases the reader to have the specious conclusion that higher doses are better.

However, there are certainly many individual case reports of higher doses being more useful.  So dose increases may have a role in some cases.

The key point is to question dose increases as a reflexive, routine management strategy for inadequate antidepressant effects.  Alternative strategies include giving the lower dose a longer try, switching to something else, or using some form of augmentation.


Just days after posting this, I see there is a new meta-analysis by Jakubovski et al. in The American Journal of Psychiatry (173:2,pp. 174-183) which suggests that SSRI antidepressants do actually work slightly better at higher doses, peaking at 2.5 times the standard dose (e.g. 50 mg fluoxetine).   They admit that the data show a trade-off between slight improved effectiveness at higher doses, but accompanied by worsened tolerability. 

Yet, it is important to consider that higher doses could reflect a greater placebo effect; some of the research about active placebos show that agents which cause more side effects are likely to have a larger impact on symptoms than inert placebos.  Because antidepressants at higher doses have more side effects, there would be more of this "active placebo" effect.  See my previous post on this subject:

It's hard to know what to make of this, other than to probably remain open-minded about the issue.  I think that a better study design for this type of issue is to look at dose comparisons within individual clinical trials, rather than to amass data meta-analytically.   Active placebo comparison groups would also be useful.  For example, agents which would cause very mild side-effects could be used instead of a totally inert placebo, so as to improve the blinding of the studies.    In many individual clinical trials of antidepressants (both new and old) which compare doses or dose ranges within the studies themselves, there are no significant differences in effectiveness.

Another issue, which the authors point out, is that most antidepressant studies have strict inclusion criteria which usually do not match the type of cases one would tend to see clinically most often.  Many studies require a major depressive disorder diagnosis, with limited comorbidities allowed, and with limited past treatment trials, etc.

Meanwhile, it remains reasonable to give a baseline dose of antidepressants an adequate length of time to work, without reflexively increasing the dose on a routine basis.   Dose increases remain an option, with some evidence-based support, but switching or augmentation could often be preferred, depending on patient preference and side-effects. 

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