If you want to get drugs and do them in BitLife, you must first create a character and become an adult. Players in BitLife will become adults when they reach age 18. Age 18 is also when most activities unlock, including one that is required to get drugs. In short, if you want drugs, you need to have the Nightlife activity unlocked, which unlocks when you turn 18. After turning 18, the Nightlife activity will appear under the Activity tab in BitLife.
That said, create your character, and after turning 18, you can get drugs by hitting up the Nightlife activity in BitLife. But getting drugs while going to the Nightclub via the Nightlife activity takes some work. This is because it's a random chance to get drugs while going to the Nightclub, as you need someone to offer them.
Luckily, you can get offered drugs fast if you keep going to the Nightclub until the event pops up. When the drug event appears, you will get offered some random drug or alcohol. Accept either one if you are trying to get drugs in BitLife for fun or to complete certain challenges.
Related: How to become a Stripper in BitLife
How to dance 15 times at a Nightclub in BitLife
If you want to dance 15 times at a Nightclub to complete challenges such as the Mike is Magical Challenge, it's easy. In short, you only need to go to a Nightclub, as every visit counts as dancing at a Nightclub. So, if you want to dance 15 times at Nightclubs, just go to a Nightclub 15 times until the objective is marked as complete. This is something easy you could work toward while trying to get drugs in BitLife.