Here is a link to an American Academy of Family Practice Journal article that puts it in context for both patients and physicians. You can link to the original research paper from there.
This echoes the experience of hundreds of millions patients and practitioners over several thousand years, but it's good to have this confirmation when examined from a western research-oriented perspective.
Acupuncture has temporary effects at first, but when reinforced in a series that typically consists of 12-15 treatments over 2-3 months, the effects can become long-lasting or even permanent.
Some patients may need periodic "booster" treatments to maintain their improvement.