Study	Reason for exclusion
Araki 2001	Acute low back pain (less than three days) was studied.
Bahrami‐Taghanaki 2014	Participants with diverse LBP etiologies were included.
Bo 2014	Acute and chronic LBP were included; chronic LBP group could not be separated out.
Ceccherelli 2002	The study included LBP due to specific and nonspecific etiologies.
Chang 2012	The study did not define the duration of LBP in inclusion criteria; chronic pain could not be separated out.
Chen 2015	The acupuncture effect could not be extracted separately from an integrative medicine approach.
Chen 2016a	Almost half of the participants had lumbar disc protrusion.
Cherkin 2001	The trial included participants who had pain for six weeks (did not meet our criteria for chronic low back pain).
Chong 2019	The study aimed to investigate LBP patients of different durations which did not meet our inclusion criteria.
Coan 1980	More than half of the included participants had sciatica.
Ding 1998	The study was designed for LBP of different durations and chronic data could not be separated out.
Dong 2014	Participants with diverse LBP etiologies included
Edelist 1976	Study did not report pain duration; disc disease was involved.
Fu 2006	The study assessed LBP patients who had suffered for less than three months as well as longer; a chronic group could not be separated out.
Garvey 1989	The trial studied acute non‐radiating low back pain.
Giles 1999	Almost half of the participants had positive findings on radiological images, accounting for specific LBP; outcomes of LBP participants could not be extracted separately from those with spine pain.
Giles 2003	Participants with LBP could not be separated from participants with spine pain.
Griswold 2019	The trial was designed for studying common LBP with different months of duration; therefore, the data for a chronic group could not be separated out.
Gu 2010	Participants with diverse LBP etiologies were included.
Gunn 1980	The chronic LBP group included some specific pain, caused by diseases such as disc protrusion and prolapsed disc.
Guo 2016	The trial was designed for investigating LBP of mixed duration.
Han 2018b	Specific pain related to the kidneys was included.
He 1997	Mixed duration of LBP; from five days to six months
Hu 2015	The study compared acupuncture and moxibustion with acupuncture and heating lamp. It did not meet the inclusion criteria of acupuncture versus another intervention.
Inoue 2000	The study investigated LBP of mixed duration.
Inoue 2001	The study was designed to investigate LBP ranging from days to months.
Inoue 2006	The study assessed specific LBP caused by lumbar vertebral arthritis diagnosed by physicians.
Inoue 2008	The study assessed LBP patients suffering from a few days to more than one year and cases with specific LBP were included.
Inoue 2009	Mixed LBP participants with different duration and etiologies were included.
Itoh 2004	Most included participants had specific LBP.
Itoh 2005	Most of the participants had LBP because of sciatica.
Itoh 2006	LBP participants with pathological changes in the lumbar spine accounted for half of the participants.
Jing 2011	Lower limb symptoms were the main manifestations of LBP.
Kawase 2006	The study was designed to investigate mixed durations of LBP.
Kim 2009	Participants with diverse LBP etiologies were included.
Kittang 2001	The trial investigated acute LBP.
Kumnerddee 2009	The study assessed 17 LBP patients with mixed duration. Chronic pain could not be separated out.
Kurosu 1979	LBP duration was not reported.
Lee 2011	The study assessed LBP lasting from less than one month, not chronic LBP.
Lee 2018	Patients had specific LBP.
Lehmann 1983	Some LBP participants had sciatica and others underwent lumbar surgery.
Li 1997	The trial was designed to investigate LBP of different durations.
Li 2005	The study compared acupuncture and moxibustion with physiotherapy, which did not meet the inclusion criteria of this review.
Li 2012	The study compared acupuncture with acupuncture and local muscle exercise, which did not meet the inclusion criteria of this review.
Li 2013	The study compared acupuncture and massage with acupuncture and massage and muscle exercise, which did not meet the inclusion criteria for two styles of acupuncture.
Li 2013a	LBP patients with different days and weeks duration were enrolled for analysis; the chronic data could not be separated out.
Li 2016	Participants with specific LBP of different duration were studied.
Li 2016a	LBP patients with a mixed duration and specific etiologies were investigated.
Li 2018	The study did not report the duration of the pain.
Lian 2005	The number of participants with specific LBP accounted for half of the sample size.
Liu 2015	The study compared lumbar electroacupuncture with electroacupuncture and muscle exercise, which did not meet the inclusion criteria of this review.
Liu 2017	Specific LBP suggested by positive images was included.
Lopacz 1979	The study assessed LBP lasting more than one month.
Macdonald 1983	Specific LBP was studied, such as pain due to a prolapsed intervertebral disc.
Marignan Michel 2014	It was unclear whether the study assessed nonspecific LBP and the randomization of this small pilot study was not explicit.
McKee 2012	Not an RCT as randomization was not mentioned.
Mendelson 1983	Patients with chronic LBP with specific etiologies were included, for example, pain due to traumatic spondylopathy and disc lesions.
Meng 2019	Study was designed for general pain of unclear duration and the characteristics of LBP were not given (meeting abstract).
Miyazaki 2009	Patients with a mixed pain duration were enrolled and investigated.
Moura 2019	The study investigated chronic back pain including upper back pain.
Muller 2005	The data from LBP participants could not be separated from data of participants with neck and back pain.
Pan 2018	Specific pain caused by spinal disc herniation was included.
Puetz 2019	The study assessed general LPB based where the duration and characteristics of the pain was not given (meeting abstract).
Sakai 1998	The trial studied LBP of various duration.
Sakai 2001	The trial studied LBP lasting more than two weeks.
Sator‐Katzenschlager 2004	LBP participants with severe skeletal changes in lumbar spine were included (40%).
Sha 2018	The acupuncture effect could not be extracted from the effects of the combined therapies.
Song 2014	Data from the chronic LBP group could not be separated out from data from the participants with mixed duration of back pain.
Sun 2010	LBP participants had pain ranging from days to months with mixed duration.
Sundberg 2009	The enrolled participants had lower back, or neck pain, or both, of mixed duration; chronic LBP could not be separated out.
Takeda 2001	Pain with or without specific etiologies was not described and pain duration was not defined. The study was designed to investigate general LBP and data from chronic nonspecific LBP could not be separated out.
Tellez‐Garcia 2015	The study compared dry needling with dry needling plus another intervention, which did not meet the inclusion criteria for two styles of acupuncture.
Thomas 1994	Pain due to specific etiologies was studied, such as sciatica and intervertebral disc degeneration.
Thomas 2005	Data from chronic LBP participants could not be separated out from data from participants with a mixed duration of pain; more than half of the participants had leg pain.
Thomas 2006	Data from chronic LBP participants could not be separated out from data from participants with a mixed duration of pain; more than half the participants had leg pain.
Tian 2016	LBP patients with different duration of pain were studied and analyzed together.
Tonev 2010	The study investigated acupuncture effects for subacute and chronic LBP together.
Toroski 2018	Not a randomized controlled trial
Tsui 2004	Specific LBP was included.
Von Mencke 1988	The study did not report the duration of LBP; pain with specific etiologies was included.
Wang 1996	The trial studied general LBP; duration of pain was not reported.
Wang 2013	We assumed that this was not an RCT as randomization was not mentioned.
Wang 2016	Data from acute and chronic LBP were studied together; data from the chronic group could not be separated out.
Wasan 2010	LBP participants with diverse etiologies were included.
Witt 2006a	Data from the chronic LBP group could not be separated out from patients with headache and pain due to osteoarthritis.
Wu 1991	The trial studied acute low back pain.
Wu 2012	Unclear the specific duration for the 40 patients it studied.
Xian 2018	Specific pain caused by spinal disc herniation was included.
Xiao 2014	We assumed that this was not an RCT as randomization was not mentioned.
Yang 2008	Sciatica was reported in more than half of the participants.
Yeung 2003	LBP participants with diverse etiologies were included.
Yu 2002	Randomization was not reported; cases like disc protrusion were included.
Yu 2010	The study compared electroacupuncture with electroacupuncture and the McKenzie method, which did not meet the inclusion criteria for acupuncture versus another intervention.
Yu 2019	The study compared massage with acupuncture combined with infrared light therapy. The effects of acupuncture alone could not be extracted out.
Zeng 2005	The study compared acupuncture and cupping with TENS, which did not meet the inclusion criteria for acupuncture versus another intervention.
Zeng 2016	Acute and chronic LBP were studied and analyzed together; it was impossible to separate out the data for the chronic group.
Zhao 2014	The study compared acupuncture and cupping with acupuncture and heating lamp, which did not meet the inclusion criteria for two styles of acupuncture.
Zhou 2010	The study compared acupuncture with another style of acupuncture plus another intervention, which did not meet the inclusion criteria for two styles of acupuncture.
Zhu 2016	Both the intervention and control group received electroacupuncture and thus the acupuncture effect could not be separated out.

LBP: low back pain; RCT: randomized controlled trial