Two teenage victims were injured in the incident on the evening of 31 March.
Michael Elmer is barred from policing after pleading guilty to five offences.
The man is in police custody, while two other men have been released under investigation.
Police say people will be "understandably shocked and upset to learn about this awful crime".
Chief constable says ratio of officers to the population in force area has been historically low.
Police began investigating when an East Somerset pharmacy reported some of its stock was missing.
A man is in custody on suspicion of administering a noxious substance and drug supply offences.
A police and crime commissioner launches the campaign around the dangers of choking during sex.
The road has reopened between Crewkerne and Ilminster and an investigation is under way.
