Depending upon the dose administered, tolazoline can reduce or neutralize the effect of clonidine, and therefore, is suitable as an antidote. Concurrent use of fenfluramine and clonidine may increase the hypotensive effects of clonidine. Sympathomimetic amines, indomethacin and possibly other nonsteroidal anti-inflammatory agents may reduce the antihypertensive effects of clonidine. The patient should be carefully monitored to confirm that the desired effect is being obtained. Clonidine may enhance the CNS-depressive effects of alcohol, barbiturates or other sedatives.
Most adverse effects are mild and generally tend to diminish with continuation of therapy.
There have been isolated reports of continual dry mouth leading to an accelerated rate of dental caries, in patients receiving clonidine. The following less frequent adverse experiences have also been reported in patients receiving clonidine, but in many cases patients were receiving concomitant medication and a causal relationship has not been established. In very rare cases pseudo-obstruction of the large bowel have been observed in predisposed patients. Vivid dreams or nightmares, other behavioral changes, restlessness, sleep disturbances, anxiety, visual and auditory hallucinations, perceptual disorders, confusion, disturbances of accommodation and delirium have been reported. Congestive heart failure and electrocardiographic abnormalities i.e., conduction disturbances and arrhythmias have been reported rarely.