Clinical presentation

Sedation and bradycardia are the most common effects of clonidine or guanfacine poisoning. These effects are usually well tolerated and require minimal intervention.

In clonidine poisoning, the onset of and peak sedation occurs within the first few hours after ingestion, but bradycardia often persists for 24 to 48 hoursIsbister, 2017. Effects can persist for longer following guanfacine poisoning, with reports of patients having symptoms for 4 to 7 days following ingestionMishra, 2022.

Effects of clonidine and guanfacine poisonings include:

• central nervous system (CNS) effects—miosis, CNS depression (ranging from drowsiness to coma), respiratory depression, seizures
• cardiovascular effects
  • early transient hypertension, hypotension
  • sinus bradycardia—a common finding on electrocardiogram (ECG); other arrhythmias have not been reported
• other effects—hypothermia.