Aspiration in intramuscular injection: a meta-analysis of pain, duration, and clinical outcomes

Aspiration during intramuscular (IM) injection is a traditional technique intended to prevent intravascular administration. However, its routine use has been increasingly debated due to potential discomfort and lack of evidence supporting clinical benefit. To systematically evaluate the effect of aspiration on pain intensity, procedure duration, and complications in IM injections through a meta-analysis of randomized controlled trials. A comprehensive literature search was conducted in PubMed, Cochrane Library, Embase, Web of Science, Scopus, EBSCOhost, TR Dizin, and PsycINFO up to May 2, 2025. Eligible studies compared aspiration versus no-aspiration techniques in IM injections. Data were analyzed using RevMan 5.4.1, with standardized mean differences (SMD) and mean differences (MD) calculated using random-effects models. Subgroup analyses were performed by age group and injection site. Risk of bias was assessed using the Cochrane ROB-2 tool. Six studies involving 693 participants were included. Aspiration significantly increased pain scores (SMD = 0.83; 95% CI: 0.31-1.35; p = 0.002), particularly in pediatric populations (SMD = 1.29; 95% CI: 1.12-1.46) and in deltoid injections. It also prolonged injection time by an average of 4.53 s (MD = 4.53; 95% CI: 3.87-5.20). No serious complications were reported in association with omitting aspiration. Aspiration during IM injections increases pain and procedure time without reducing complication risk. These findings support current international guidelines discouraging routine aspiration, particularly in pediatric and vaccine-related applications. Injection technique should be individualized based on patient characteristics and medication type.