In water-based muds, as incorporation of drilled solids progressively influences the mud rheology, it may be of significant benefit to reduce the viscosity of drilling fluid using a thinning agent (deflocculant). These highly effective products avoid the need for mud dilution which also requires replenishment of mud chemicals and increases mud volume and disposal costs. In addition, once present, thinners will maintain a dispersed drilling fluid rheology, thus protecting against mud gelling or flocculation due to contamination and / or high temperature. This in turn will help achieve a thin filter-cake at the wellbore and will avoid excess fluid loss and associated issues.