Using a global time-dependent general circulation model, we calculate the distribution of constituents in Titan's thermosphere resulting from transport caused by winds and molecular and eddy diffusion. Our simulations reveal that thermospheric winds effectively mix constituents in Titan's upper atmosphere. Consequently, the large eddy coefficients inferred from Voyager UVS observations may be a result of vigorous thermospheric circulation on Titan. Thermospheric winds also cause large diurnal variations in composition, with equatorial CH4 mole fractions near 1400 km ranging from ~15% in the late afternoon to ~58% in the early morning at equinox.