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When a significant amount of an anticholinergic is taken into the body, a toxic reaction known as acute anticholinergic syndrome may result. This may happen accidentally or intentionally as a consequence of recreational drug use. Anticholinergic drugs are usually considered the least enjoyable by many recreational drug users, possibly due to the lack of euphoria caused by them. There have been reported cases of users experiencing what they attribute to "euphoria" from the use of this substance. It also can produce extremely vivid hallucinations (visual, auditory, tactile) which often can not be distinguished from reality; this can cause intense fear and panic and is more often considered to be a poison rather than a recreational substance by those who have experimented with this class of drug. In terms of recreational use, these drugs are commonly referred to as deliriants. Because most users do not enjoy the experience, they do not use it again, or do so very rarely. The risk of addiction is low in the anticholinergic class. The effects are usually more pronounced in the elderly, due to natural reduction of acetylcholine production associated with age.
Acute anticholinergic syndrome is completely reversible and subsides once all of the causative agent has been excreted. Reversible cholinergic agents such as physostigmine can be used in life-threatening cases. Wider use is discouraged due to the significant side effects related to cholinergic excess including: seizures, muscle weakness, bradycardia, bronchoconstriction, lacrimation, salivation, bronchorrhea, vomiting, and diarrhea. Even in documented cases of anticholinergic toxicity, seizures have been reported after the rapid administration of physostigmine. Asystole has occurred after physostigmine administration for tricyclic antidepressant overdose, so a conduction delay (QRS > 0.10 second) or suggestion of tricyclic antidepressant ingestion is generally considered a contraindication to physostigmine administration. 
Certain preparations of some drugs with abuse potential, such as hydrocodone, are mixed with an anticholinergic agent to deter intentional overdose. Examples include Hydromet/Hycodan (hydrocodone/homatropine) and Lomotil (diphenoxylate/atropine).
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