Downer (noun)

1. Something that depresses or discourages.
2. A drug that has a sedative effect.

Origin:

1930s: from down + -er.

Examples:

1. The bad news was a real downer.
2. The rain was a downer on an otherwise beautiful day.
3. He took a downer to help him sleep.
4. The downer made him feel calm and relaxed.
5. The downer made him feel drowsy and he couldn't stay awake.