In psychiatry and pharmacology, dependence refers specifically to pathological phenomena resulting from repeated use of psychoactive substances. Corresponding pharmacological experimental methods and related guiding principles have been formulated for the reinforcing effects, tolerance, physical dependence and mental dependence of psychoactive drugs, thereby proving the psychoactive effects experimentally. In the 10th edition of the International Classification of Diseases, the title of mental disorders coded F10-F19 is: “Mental and behavioral disorders caused by the use of psychoactive substances”, and dependence syndrome is the exclusive diagnostic term for this type of disorder. “Mental and behavioral disorders caused by the use of psychoactive substances” is what addiction psychiatry is all about.
In clinical work, withdrawal symptoms are considered to be an important manifestation of dependence syndrome. However, non-psychoactive drugs, such as paroxetine, can cause withdrawal symptoms when use is suddenly stopped; psychoactive substances such as cocaine and methamphetamine rarely produce withdrawal symptoms. For non-psychoactive drugs that can produce withdrawal symptoms, the body reaches a new equilibrium state during use. Stopping the use of the drug may break this balance and cause withdrawal reactions (withdrawal symptoms).
Trihexyphenidyl is an anticholinergic drug. During long-term use, the body can compensatoryly enhance choline function to adapt to the pharmacological effects of trihexyphenidyl against choline and achieve a balance. The balance of this adaptation is disrupted when trihexyphenidyl is discontinued. Enhanced choline function can produce discomfort and cause withdrawal symptoms. In this case, the patient may continue to use trihexyphenidyl and be considered to be dependent.
In fact, the term “dependence” is inappropriate to describe this phenomenon. Because, dependence is only for psychoactive substances. Trihexyphenidyl is not a psychoactive substance. Withdrawal from nonpsychoactive substances is not a dependence syndrome. Strictly speaking, the patient only had withdrawal symptoms, which was a drug withdrawal reaction.
It goes without saying that the use of trihexyphenidyl in psychiatry has a tendency of serious abuse. Some clinicians advocate preventive medication and increase the frequency of trihexyphenidyl use. Trihexyphenidyl is currently the most widely used drug in psychiatry. In fact, some scholars have long believed that, just as the preventive use of anticholinergic drugs is not advocated, the long-term combined use of trihexyphenidyl should also be used with caution. Even if it is used, it should be gradually withdrawn within 3 months. Antipsychotics long-term block dopamine type 2 receptors (D2), leading to a compensatory increase in D2 receptor sensitivity (hypersensitivity), alleviating the D2 receptor blocking effect, and tending to tolerate acute extrapyramidal reactions (EPS) , In some patients, EPS symptoms will disappear automatically after 7-10 days of adaptation. Therefore, for patients taking medium and low-dose antipsychotics, trihexyphenidyl can be withdrawn on a trial basis after taking them for 3 months.
Withdrawal symptoms caused by trihexyphenidyl are a serious adverse reaction that may lead to continued use and long-term abuse of this drug. The adverse reactions caused by psychiatric drugs are quite prominent, and trihexyphenidyl, which is used to control drug-induced EPS, can also produce obvious adverse reactions. This issue has not received the attention it deserves, so there are constant reports of trihexyphenidyl withdrawal cases.
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