Trihexyphenidyl (THP, benzhexol, trihex, marketed as Artane and others) is an antispasmodic drug used to treat stiffness, tremors, spasms, and poor muscle control.

Trihexyphenidyl may improve psychotic depression and mental inertia frequently associated with Parkinson's disease and symptomatic problems caused by antipsychotic treatment.

[medical citation needed] The drug cannot cure Parkinson's disease, but may provide substantial alleviation of symptoms.

[11] In organophosphate poisoning, trihexyphenidyl is a more effective antidote than atropine to counteract the cholinergic crisis, seizures, and neuropathology.

[12] Equivocal preliminary results from small studies exist for other dyskinesias, Huntington's chorea, Spasmodic torticollis.

All of the following symptoms considered, Artane has been shown to dramatically and consistently improve neurologic defects in people aged 16–86 over the course of five years.

[18] Overdose mimics an atropine intoxication with dryness of mucous membranes, red face, bowel and bladder paralysis, and hyperthermia in high doses.

[21][22] 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).

[27] In the US, the FDA approved Artane, or its generic form Trihexyphenidyl HCL, only on June 25, 2003 for the clinical use of all types of parkinsonism.

[29] He recalled taking "a large dose" knowing full well the drug was intended for people with Parkinson's.

More recounts of Dr. Sacks' experiences — including experimentation with mescaline, psilocybin, LSD, and probably DMT[30] — have been compared in his book Hallucinations.

[31] In a 2008 news report, trihexyphenidyl was seen to be used for recreational purposes among Iraqi soldiers and police, among other prescription drugs.

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.