Does the placebo effect persist over time?

[Posy McPostface]

I've have seen many PANSS and MADRS graphs showing the magnitude of the placebo effect in psychiatric disorders, which is astonishing in isolation.

However, many studies quit the placebo after 4-6 weeks, despite the placebo effect being in full force and not remitting for the duration of administration.

Thus, does the placebo effect taper off or decline with time in other studies that administer it beyond the 4-6 week duration?

Thanks.

 

[jim mcnamara]

https://www.ncbi.nlm.nih.gov/pubmed/18437321

There is no fixed duration for the placebo effect - it varies a lot. The longest one observed is about a few weeks. Asking beyond that makes no sense - nobody seems to know and they are never going to keep a patient (except for severely insane or incapacitated patients) in a clinic for years just to answer idle curiosity. This is more clinical than anything else - physicians examining patients and determining how they feel, so they need to see patients almost daily.

And assesing very disturbed people is not a good representative sample of normal human response. Especially since the response is thought to be mediated by the brain and patient inputs. And other factors change the response as well:

Kam-Hansen S, Jakubowski M, Kelley JM, Kirsch I, Hoaglin DC, Kaptchuk TJ, Burstein R. Altered placebo and drug labeling changes the outcome of episodic migraine attacks. Sci Transl Med. 2014 Jan 8;6(218):218ra5. PubMed You may not be able to see more than the abstract.

-This one says that simply changing a drug label can alter response to the drug.