A low toxicity composition and method of reducing the swelling of clay in well comprising circulating in the well a water-based fluid comprising a functionally effective concentration of the additive formed from the following reaction of a tertiary amine of the following general formula: wherein R1 and R2 are alkyl or hydroxyalkyl groups with one to three carbon atoms or combinations thereof, and R3 is a hydroxyalkyl group with one to three carbon atoms, with an alkylating agent of the following general formula: R-A wherein R is an alkyl radical with one to three carbon atoms, and A is an organic or inorganic anion selected from the group consisting of sulfate, phosphate, carbonate, and combinations thereof.