Sedatives (or ‘downers’) are a category of drugs that slow down normal brain function. There are two basic groups of sedatives;
– Opioids; Similar to established recreational opioids, but with the potential for much longer durations of action.
– Benzodiazepines; Sedative, anxiolytic, hypnotic, and anticonvulsant properties–some with long duration of action.
These NPS act like benzodiazepines, opium, heroine.
Examples are MT-45, AH-7921 and novel fentanyls (opioids) or diclazepam and flubromazepam (benzodiazepies)

Short term risks include overdose, confusional states en seizures (after withdrawal)
Long term risks include addiction and impaired cognition
The risk are heightened particularly when mixed with alcohol or other sedatives.

Sedatives are snorted, smoked, injected or swallowed

For more (fairly technical) information on the different sedatives, you can visit this Wikipedia page. Be aware though, that this page is not scientifically checked.

Source: 1, 2, 3