If you’re asking this, you likely haven’t tried a heavy dose of high thc indica strain cannabis. Weed strains with 15+ thc percentage tend to have the most dramatic ability to make one sleepy as fuck. Generally these include the OG type strains, especially the planetary (Earth OG, Saturn OG, etc) and the newly trending Gorilla Glue #4. Many strains will make you moderately tired, but it always depends on the amount you smoke and intake. The sleepiness can always be counteracted with coffee or an energy drink, which may explain why so many weed shops in Europe are “coffee shops”
Dabs of indica strain cannabis will also help increase your ability to sleep and nap in a seconds notice. I recommend 2-3 dabs before bed for a great night’s sleep.