Tranquillisers can be divided into 2 main classes - Barbiturates, and Benzodiazepines.  The former are less common these days, as Bnezodiazepines, despite a higher addiction potential, are considered safer for short periods of use.
Normally by doctor's prescription, but sold illegally on the street.
Normally come as pills or capsules.

METHOD OF USE

Usually swallowed.
Can be injected.

THE LAW

CLASS:  C
 
Possession:
Up to 2 years imprisonment and/or an unlimited fine.

Supply:
Up to 14 years (life) imprisonment and/or an unlimited fine.

EFFECTS/SIGNS OF USE

• Users can feel relaxed, sleepy, depressed, sick, forgetful and sometimes violent
• They appear 'out of it' and lack coordination
• Similar indications to being drunk on alcohol

DANGERS/RISKS

• Very dangerous if used along with alcohol
• Accident prone
• Both mentally & physically addictive
• Very difficult to stop using, and sudden withdrawal can be dangerous
• High risk of overdose