Several of these drugs will initially cause tachycardia (due to anticholinergic or adrenergic effects), with bradycardia only occurring in severe poisoning.

• Tricyclic antidepressants
• Antipsychotic drugs (particularly chlorpromazine and thioridazine)
• Antimalarial drugs (chloroquine, quinine)
• Antiarrhythmic drugs
• Orphenadrine