Antipsychotics : Long term use of trihexyphenidyl  may mask or increase the risk of tardive dyskinesia. Pethidine (meperidine) : Central effects and side effects of pethidine may be increased. Metoclopramide : Action of metoclopramide is decreased. Alcohol : Risk of serious intoxication. Pharmacology
The exact mechanism of action in parkinsonian syndromes is not precisely understood, but it is known that trihexyphenidyl blocks efferent impulses in parasympathetically innervated structures like smooth muscles (spasmolytic activity), salivary glands, and eyes (mydriasis). In higher doses direct central inhibition of cerebral motor centers may contribute. In very high doses central toxicity as seen in atropine overdose is noted. It binds to the M1 muscarinic receptor and possibly the dopamine receptor. Trihexyphenidyl is rapidly absorbed from the gastrointestinal tract. The onset of action is within 1 hour after oral dosing. The peak activity is noted after 2 to 3 hours. The duration of action of one single dose is 6 to 12 hours in a dose dependent manner. It is excreted in the urine, probably as unchanged drug. More precise data in animals and humans have so far not been determined. History
Artane, or its generic form Trihexyphenidyl HCL, was approved by the FDA on June 25, 2003 for the clinical use of all types of parkinsonism. However, it has been clinically relevant in trials pertaining to Parkinsons disease since 1949. Artane is an anticholinergic drug which is prescribed by doctors throughout the world. It is also abused, typically in combination with other drugs or delicate pharmaceutical agents.
Prisons in Iraq were among the places where abuse was obvious, along with within communities of Iraqi soldiers. Society and culture
Recreational use
In a 2008 news report, trihexyphenidyl was seen to be used for recreational purposes among Iraqi soldiers and police, among other prescription drugs. The report states that the drugs were taken to relieve combat stress. Although that may be the case for some, others used Artane as a substitute or more intense version of LSD. This was especially prevalent in the 1960s, according to a report in "The New Yorker". Similarly to those in Iraqi forces, some of the appeal was that the individual may retain partial control while under the influence.The neurologist Oliver Sacks reports using the drug recreationally in the 1960s. He recalled taking "a large dose" knowing full well the drug was intended for people with Parkinsons. More recounts of Dr. Sacks experiences — including experimentation with mescaline, psilocybin, LSD, and probably DMT — have been compared in his book Hallucinations. During the 1970s, trihexyphenidyl(trade name Parkan) was the most popular recreationally used prescription drug in Hungary. Chemistry
Trihexyphenidyl can be synthesized in two ways, one linear and one convergent synthesis. In the first way, the initial 2-(1-piperidino)propiophenone is synthesized in turn by the aminomethylation of acetophenone using paraformaldehyde and piperidine in a Mannich reaction. In the second step the 2-(1-piperidino)propiophenone is reacted with cyclohexylmagnesium bromide in a Grignard reaction. Stereochemistry
Trihexyphenidyl has a chiral center and two enantiomers. Medications are racemates.