Fused deposition fabrication (FDF) three-dimensional printing is a potentially transformative technology for fabricating pharmaceuticals. The state-of-the-art technology is still in its infancy and requires a concerted effort to realize its potential. One aspect includes the processing parameters of FDF and the effect of formulation thereto, which, to date, have not been thoroughly investigated. To progress understanding, the effect of different molecular weight poly(ethylene glycol)s (PEG) on polycaprolactone (PCL) loaded with ciprofloxacin (CIP) was investigated. A rheometer was used, and adapted accordingly, to analyze three processing aspects pertaining to FDF: viscosity, solidification, and adhesion. The results revealed that both CIP and PEG affected all three processing parameters. The salient findings were that the ternary blend with 10% w/w PEG 8000 exhibited rheological and adhesive properties ideal for FDF, as it provided a desirably shear-thinning filament that solidified rapidly, and improved the adhesion strength, in comparison to both the PCL-CIP binary blend and other ternary blends. In contrast, the ternary blend with 15% w/w PEG 200 was unfavorable; despite having a greater plasticizing effect, whereby the viscosity was markedly reduced, the sample provided no benefit to the solidification behavior of PCL-CIP and, in addition, failed to display adhesive behavior, which is a necessity for a successful print in FDF. The original findings herein set the precedent that the effect of drug and PEG on FDF processing should be considered beyond solely modifying the viscosity.