Within a huge global organisation as the WHO, there is a lot of lobbying between groups promoting evidence based medicine and promoters of traditionally and complementary treatments, as described here.
The book Trick or Treatment? Alternative Medicine on Trial by Edzard Ernst and Simon Singh devotes a lot of attention to the WHO's policy
This list of people, organizations and entities responsible for the
unwarranted growth of ineffective and sometimes dangerous alternative
medicine has been in no particular order, except that the World Health
Organization (WHO) has been deliberately chosen to complete the list
as it holds a special position. No organization has done more to
improve health around the world, such as the eradication of smallpox,
and yet the WHO has acted shamefully in its attitude and actions
towards alternative medicine. We would have expected it to provide
clear and accurate guidance about the value of each popular
alternative therapy, yet in 2003 the WHO muddied the waters by
publishing a highly misleading document on the value of acupuncture.
Entitled Acupuncture: Review and analysis of reports on controlled
clinical trials, the report based its conclusions on several
unreliable clinical trials and thus endorsed acupuncture as a
treatment for over 100 conditions. Of course, the evidence from
high-quality reliable clinical trials paints a very different picture.
In reality, acupuncture might possibly (though it looks less possible
as each year passes) be effective in treating some types of pain and
nausea, but it offers no proven benefit for any other conditions.
Naturally, ever since its publication, acupuncturists have cited the
WHO report as the most authoritative evaluation of their mode of
healing. And, not surprisingly, prospective patients have been
persuaded that acupuncture must be effective for a whole range of
conditions, because, after all, it has the blessing of the WHO.
However, the WHO report was a shoddy piece of work that was never
rigorously scrutinized and which should never have seen the light of
day. The WHO could repair its reputation if it were prepared to re
evaluate acupuncture fairly and publish a new report that reflected
the evidence from the latest and most reliable trials. In this way, it
could make a huge contribution to the public’s understanding of what
acupuncture can and, more often, cannot treat. Unfortunately, there is
no sign that this is likely to happen.
The WHO's strategy on traditional medicine strategy: 2014-2023 is like committee work rather vague on this issue.