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Pharmaceuticals in aquatic environments have been put under increasing scientific scrutiny as they are frequently found as contaminants in natural waters, often entering via effluent water containing pharmaceutical residue from human excretion. Diclofenac is a frequently found non-steroidal anti-inflammatory drug [NSAID] in waters that has been shown to cause both acute and chronic effects on various aquatic organisms. A common method to assess the effects of sub-lethal exposures has been behavioral experiments, yet these tests are often not considered in regulatory decision-making. This study aimed to evaluate if diclofenac can cause behavioral changes in fish through a meta-analysis of existing literature. A total of 372 studies, identified from six different databases, were reviewed. A random-effects model was applied on four studies where behaviors acting as proxies for fish activity were measured in response to diclofenac exposure. It was found that diclofenac does not seem to affect the activity in fish in neither light nor dark conditions, with one potential exception at high exposure levels (>100 μg/L) in light conditions causing decreased activity. A comparison using available monitoring data in waters from national databases (including sampling between years 2005 and 2021) was used to illustrate that diclofenac concentrations in Sweden, and globally, do not exceed this latter value. Therefore, it appears unlikely that diclofenac will influence the activity in fish.