Somnifacients are things that make you sleepy or help you sleep.
Somnifacients are usually thought of as helpful, especially for people who have trouble sleeping.
Examples:
She takes somnifacients to help her sleep at night.
The doctor prescribed somnifacients for his insomnia.
The somnifacients made him feel drowsy.
The somnifacients worked like magic and he fell asleep instantly.
After taking the somnifacients, she slept for 12 hours straight.
The somnifacients are like a lullaby for adults.