Dimethyl sulfoxide (DMSO) is commonly used as a solvent for preparing amyloid-beta (Aβ) peptides implicated in Alzheimer's disease. While considered relatively non-toxic at low concentrations, DMSO itself may exert biological effects that could confound experimental outcomes, especially for weakly cytotoxic substances like Aβ. Seven brain cell types (BV-2, N2a, SH-SY5Y, U87, neurons, astrocytes, microglia) were treated with varying DMSO concentrations or Aβ1-42 oligomers/protofibrils/fibrils prepared using DMSO. Cell viability was assessed by CCK-8 and LDH assays. Matched DMSO controls were prepared alongside Aβ treatments to delineate solvent effects. Low DMSO concentrations (0.0625-0.015625%) exhibited hormetic cytoprotective and growth-promoting effects, while higher concentrations (≥2%) were cytotoxic. Importantly, these hormetic solvent effects confounded the measurement of Aβ cytotoxicity. By accounting for matched DMSO controls, the study revealed that Aβ fibril toxicity may have been underestimated due to the cytoprotective solvent effects of low DMSO concentrations used in their preparation. In conclusion, DMSO exhibits complex hormetic dose-responses that can significantly influence experimental outcomes, especially for weakly cytotoxic agents like Aβ. Rigorous solvent controls are crucial to delineate genuine substance effects from potential solvent confounds and avoid erroneous interpretations.