Scopolamine (also referred to as hyoscine hydrobromide or scopolamine hydrobromide) is a drug used for motion sickness.
Scopolamine is used to treat motion sickness, sea sickness (leading to its popularity with scuba divers), gastrointestinal spasms, renal or biliary spasms, irritable bowel syndrome, clozapine-induced drooling, bowel colic, and eye inflammation. It is also used, in some cases, as a pre-medication to surgeries, usually those meant to reduce respiratory tract secretions.
Uncommonly, there are side-effects to using the drug. They usually range from a dry mouth to itching. Rarer side-effects include agitation, confusion, restlessness, and even hallucinations, though these have a probability of less than 0.1% in occurrence.
In Mr. Scratch, serial killer by proxy Peter Lewis used scopolamine as an ingredient for an extremely powerful dissociative agent, which would induce psychotic breaks in potential victims. Reid states that the drug makes people highly suggestible. Following his escape from prison in Season Eleven, Peter resumed using scopolamine for his newest crime sprees in Season Twelve. In Spencer, scopolamine was also apparently used by hitwoman Lindsey Vaughan when she attempted to frame Reid for a Peter-inspired murder.
The series depicts the administration of scopolamine (via air vents) inaccurately, as the drug only exists in a liquid or powder form, making said administration implausible. The drug also takes at least ten minutes to start taking effect when it is injected directly, or up to four hours if absorbed through the skin; in the episode, the drug's effects seem to be near-instantaneous.