Dysphagia has been associated with a high risk of undernutrition and aspiration pneumonia in the elderly. It is commonly managed by adding commercial thickening agents to thicken liquids. The rheological behavior of these thickeners in water is known but there is lack of information with regard to other liquids. The aim of this study was to determine the viscosity of 11 beverages after adding commercial thickeners and to compare their viscosity with that of thickened water and also with the reference limits of the National Dysphagia Diet (NDD). We added starch-based and gum-based thickeners to 11 beverages to achieve a honey-like consistency. The 11 beverages were five juices (apple, orange, grape, peach-grape, and pineapple), two teas (black tea and chamomile), milk (whole and skimmed), instant coffee, and a vegetable milk (tigernut milk). Viscosity measurements were made in a controlled environment for the resulting 22 samples. Compared to thickened water, significant changes were found for all beverages except apple juice, with both starch- and gum-based thickeners, and orange juice, pineapple juice, and chamomile with the gum-based thickener. Results with respect to the NDD reference limits showed significant changes in viscosity only for peach-grape juice and pineapple juice with starch-based thickener. These findings show that changes arise in the viscosity of some thickened beverages compared to thickened water and also compared to the range recommended by the NDD. Further studies are needed to describe the rheological behavior of other beverages, thickeners, and consistencies. Recommendations to ensure feeding safety may be required for elderly patients with dysphagia.