Tranquilliser
drug that induces tranquility in an individual
Tranquillisers are drugs produced to treat anxiety, depression and insomnia. Prescribed by a doctor, they are designed to reduce anxiety, and promote calmness, relaxation and sleep. There are hundreds of different tranquillisers around, but most common are the benzodiazepines. Rohypnol is one of the most strongly-acting tranquilisers. "Tranquilliser" is also a colloquial way of saying "dart gun".