- A placebo-controlled study of guanfacine in the treatment of children with tic disorders and attention deficit hyperactivity disorder. Scahill, L., Chappell, P.B., Kim, Y.S., Schultz, R.T., Katsovich, L., Shepherd, E., Arnsten, A.F., Cohen, D.J., Leckman, J.F. The American journal of psychiatry. (2001)