Speed effects
"Speed" usually refers to amphetamine, a powerful stimulant that can make you feel awake, energetic, and euphoric. Typical effects include increased drive, less need for sleep or food, and a strong boost in focus.
At the same time, the effects can quickly flip to the opposite: Nervousness, rapid heartbeat, restlessness, anxiety, or exhaustion after it wears off are common side effects, especially with frequent or high doses.
If you want to learn more about effects, risks, and background info, you'll find some helpful content here: