Central effects of guanfacine and clonidine during wakefulness and sleep in healthy subjects.

1. Three double‐blind studies in young normotensive male volunteers were carried out: a study in ten awake subjects, comparing guanfacine 2.0 and 4.0 mg with clonidie 0.15 and 0.30 mg and placebo; and two polygraphic sleep studies each with six subjects, comparing guanfacine 1.0 and 2.0 mg with placebo, and clonidine 0.15 and 0.30 mg with placebo, respectively. 2. In awake subjects, both drugs reduced systolic blood pressure without significantly altering diastolic blood pressure, pulse rate and objective performance parameters. 'Side‐ effects' such as tiredness, decreased inclination to work, and dryness of the mouth were somewhat more frequent after the higher clonidine dose than after both doses of guanfacine, and peaked 2 h after clonidine but only 4‐6 h after guanfacine. 3. Clonidine 0.15 and 0.30 mg given in the evening was followed by a substantial and dose‐ dependent reduction in rapid eye movement (REM) sleep. Guanfacine 1.0 mg did not alter REM sleep and 2.0 mg of guanfacine had less effect than both doses of clonidine in this respect. Clonidine's effect on REM sleep began after about 2 h, whereas guanfacine's action on REM sleep began 5 h after the dose. 4. Guanfacine and clonidine possess a qualitatively similar pattern of activity with regard to the parameters studied; but the central effects are less pronounced and occur later after guanfacine than after clonidine in equiactive doses.