Knee osteoarthritis (KOA) is more common in women and ranks among the leading causes of disability and chronic pain worldwide.1 It is characterized by cartilage degradation, subchondral bone changes, osteophytes, and local synovial inflammation, culminating in pain and disability.2 KOA also imposes a significant socioeconomic burden, due to its high treatment costs, and its associations with disability, early retirement from work, and even mortality.3–5

Clinical practice guidelines recognize that the therapeutic approach for people with KOA must include non-pharmacological strategies.6–8 Among these, cupping therapy has been widely used to treat pain9–11 and functional capacity.9 It is believed that suctioning the area may increase the supply of fresh blood to the area, thereby accelerating the removal of metabolites and promoting recovery. In addition, other theories have been proposed to explain the effects of dry cupping on pain, such as the pain gate theory, diffuse contractile inhibitory control, and reflex zone theory.12,13

Efficacy of cupping is known to be controversial, and the heterogeneity14 of the studies contributes to the uncertainty about its real benefits. Two systematic reviews12,15 showed high heterogeneity between studies and a high risk of bias. Several limitations were reported, such as lack of blinding, inadequate randomization, lack of follow-up, lack of a control group, and short intervention time,12,15 which weaken the certainty of the evidence and highlight the need for well-designed clinical trials with a robust methodology.12,15

The purpose of this study was to evaluate the effects of dry cupping on pain at rest and with movement in women with KOA. The secondary objectives were to evaluate the effects of dry cupping and sham cupping on functional performance, quality of life, use of analgesics and anti-inflammatories, and the degree of expectation and global perceived effect (GPE) with treatment after the intervention protocol. Our study was designed to address the limitations identified in previous research on the use of cupping in KOA, using a more robust protocol with 12 visits over 6 weeks, followed by a one-month post-intervention follow-up to assess both post-intervention and short-term effects.

A total of 96 participants were initially selected for the study. Of these, 62 met the eligibility criteria and were randomized after the initial assessment. Of the randomized participants, 57 completed all intervention procedures. Five participants in the control group discontinued treatment after the third week, resulting in an 8 % dropout rate. The multiple imputation method outlined in the statistical analysis was used for the missing data. Reasons for dropping out included increased knee pain after cup application. No participants in the experimental group discontinued treatment (Fig. 1).

Fig. 1.

Design and flow of participants through the trial.

During the intervention period, 27 participants (87 %) in the experimental group used analgesics and/or anti-inflammatories, while 26 participants (84 %) in the control group used these medications. In terms of the number of absences during treatment sessions, there were no more than three absences per participant in either group.

Demographic characteristics of participants in both groups were similar at T0. The mean (standard deviation [SD]) age and mean body mass index were 60.4 (6.3) years and 30.8 (4.7) kg/m2 for the experimental group and 60.0 (5.7) years and 31.7 (4.5) kg/m2 for the control group. Approximately 55 % of the sample reported the right knee as the most troublesome knee, and more than 85 % were taking medication at the time of evaluation. Other sample characteristics are described in Table 1.

Tables 2 and 3 present the clinical data for both groups at T0, T3, T6, and T10 (follow-up). The between-group and within-group differences are presented for all outcomes, including pain at rest and during movement, functional capacity tests (i.e., STS-30, 8-step SCT, 40mFPWT), WOMAC, quality of life, and GPE at different time points. No between-group differences for the primary outcomes, pain at rest and during movement, and any of the secondary outcomes were observed. Only within-group differences for some variables were observed.

Regarding the effectiveness of the strategy to blind the participants, in the experimental group, 25 participants (81 %) believed they had received dry cupping therapy, while 6 participants (19 %) believed they had received sham therapy. In the control group, 19 participants (73 %) believed they had received dry cupping therapy, while 7 participants (27 %) believed they had received sham therapy. There was no difference between groups (p > 0.05) (Table 4).

In the experimental group, 31 participants (100 %) reported that they felt a suction sensation during the interventions, with 16 of them (52 %) mentioning that they felt the sensation at the place where the treatment was applied (suction cup area). Mean (SD) intensity of the suction sensation reported by this group was 63.2 (24.0). In the control group, 24 participants (92.3 %) also reported feeling a suction sensation during the interventions, with 15 participants (57.7 %) mentioning that they felt the sensation at the place where the treatment was applied (suction cup area). The mean (SD) suction sensation reported by this group was 61.9 (24.6) (Table 4). In addition, when analyzing the participants’ reports of the characteristics of the sensations experienced, we observed that only the sensation of “pressure” showed a significant difference (p < 0.01). No adverse events were observed in the groups studied or reported by the participants.

This is the first clinical trial to compare dry cupping therapy with sham cupping in women with KOA, evaluating outcomes of pain intensity, functional capacity, quality of life, and perceived overall effect. At weeks three, six, and ten after initiating treatment, both groups showed similar reductions in pain intensity, with no significant differences between them at any time point. No clinically valid effects of dry cupping therapy were confirmed in secondary outcomes. These results question the efficacy of dry cupping therapy as a non-pharmacological option for the treatment of KOA.

Although a systematic review14 indicated that dry cupping therapy may reduce pain and improve functional capacity in people with KOA, the strength of this conclusion is undermined by the heterogeneity and low methodological quality of the studies analyzed. Therefore, these results must be interpreted with caution, as not all included studies had a control group for comparison, limiting the ability to evaluate the true effectiveness of dry cupping therapy. However, our findings, using a more robust methodological design with rigorous control, intention-to-treat analysis, a sham-controlled group, and appropriate comparison group, provide new evidence that may contribute to a more accurate assessment of the efficacy of this therapeutic approach for KOA.

Our results contrast with those of Teut et al., who reported significant improvements in pain, WOMAC, and quality of life after eight cupping sessions over four weeks.37 However, their study had methodological limitations such as the lack of a control group, lack of blinding, and did not perform an intention-to-treat analysis. Moreover, authors did not perform a sample size calculation, which raises concerns about the reliability of their findings. A small sample size increases the risk of type I error, which means that observed benefits may have been due to chance rather than a true effect of the intervention.37 Islam et al. showed a significant effect of cupping combined with deep massage in people with KOA, for improving outcomes such as pain, activities of daily living, recreational activities, and quality of life.38 The protocol consisted of 15-minute sessions on alternate days for a total of 10 sessions over 20 days.38 Nevertheless, this study also had a high risk of bias due to lack of blinding, small sample size, short duration, and lack of post-intervention follow-up (to assess medium-term efficacy), again raising the possibility of overestimating the effects of the intervention. In contrast, our findings, with a more robust methodological design, larger sample size, rigorous bias control, and adequate post-intervention follow-up, provide more reliable evidence and a more accurate assessment of the efficacy of this intervention in people with KOA.

Results of the present study also challenge the primary mechanisms proposed to explain the pain-relieving effects of dry cupping therapy for people with KOA. Three theoretical bases have been suggested to explain the physiological effects of pain reduction after the use of dry cupping therapy: the pain portal theory,39 the diffuse inhibitory control theory,40 and the reflex zone theory.12 However, these theories are unlikely to explain the totality of the analgesic effect, because the participants in the sham cupping group showed similar improvements to the dry cupping therapy group. Given the results of the current study, the placebo effect,41 positive expectations regarding the treatment,42 the therapist-patient alliance (Hawthorne effect),43 and the environmental context are factors that most likely explain the improvements observed in the participants44 with the cupping intervention.

For the secondary outcomes, the mean differences between groups clearly excluded the possibility of clinically significant effects of cupping on the functional capacity, quality of life, and global perceived effect. The estimated effects for secondary outcomes were below the minimum clinically significant thresholds, and all 95 % CIs indicated no effect. Therefore, there was no clinically significant effect of dry cupping therapy on any of the secondary outcomes for people with KOA.

Similarly, Islam et al. used the same intervention for people with KOA. However, their sample was small (total, n = 40) and weak (β = 90 %), whereas our sample size (n = 62) and statistical power were greater (β = 80 %); their a priori estimate of sample loss was 20 %, whereas ours was 10 %; they did not use an intention-to-treat in their data analysis, and their sample attrition exceeded 15 %, as suggested by the PEDro scale, whereas ours had 5 % dropout rate.38 The clinical implications of our findings are relevant to health care systems and clinicians. Given the lack of proven benefit of dry cupping therapy beyond placebo effects and other contextual factors, resources could be better allocated to interventions with stronger evidence of effectiveness, such as structured exercise programs and patient education. These findings highlight the importance of high-quality research to guide clinical decision making and prevent the proliferation of ineffective treatments.

Clinicians should be aware of the limited effectiveness of dry cupping therapy and consider prioritizing interventions such as exercise therapy and patient education, which have stronger scientific support, for the management of KOA.45,46 Additionally, educating patients about the evidence (or lack thereof) behind different treatment options is essential to promote informed decision-making and prevent the use of ineffective therapies that may lead to unrealistic expectations or unnecessary healthcare costs.47,48

There are limitations to our study that need to be considered. Only women were included; therefore, it is unknown whether these results are generalizable to men with KOA. Due to the nature of the intervention, it was not possible to blind the therapist responsible for delivering the intervention to the participants in both groups. The irregularity of the knee area, which varied according to the anatomy of each participant, made it difficult to apply the suction cups. In addition, more than 80 % of both groups were taking medications, which may be a confounding variable in terms of prognosis.49,50 Finally, the negative pressure created by the suction cups could vary from 100 to 300 millibars, and we did not evaluate the mean of these data; the conclusions of this study were limited to the application of dry cupping therapy in isolation, which may not reflect the treatment typically provided by therapists in their clinical practice. Future studies should consider including both sexes, standardizing suction pressure, and evaluating potential long-term effects beyond the intervention period.

Dry cupping therapy was not superior to sham cupping in improving pain, functional capacity, quality of life, and global perceived effect in women with KOA. Until more robust evidence of efficacy is available, practitioners should reconsider the use of dry cupping in people with KOA and advise them to consider interventions based on the best available evidence.

RRC and MCS – Conceptualization, Investigation, Data curation. All authors – Formal Analysis, Methodology, Validation, Visualization, Writing (original draft, review, and editing).

The data and materials in this paper are available from the corresponding author on request.