α-Pyrrolidinopropiophenone (α-PPP) is a stimulant

Stimulant

Stimulants are psychoactive drugs which induce temporary improvements in either mental or physical function or both. Examples of these kinds of effects may include enhanced alertness, wakefulness, and locomotion, among others...

 drug. It is similar in structure to the appetite suppressant diethylpropion and has analogous effects in animals. Little is known about this compound, but it has been detected by laboratories in Germany as an ingredient in "ecstasy" tablets seized by law enforcement authorities. This drug has been found to produce stimulant effects in animals and presumably also produces these effects in humans, based on the context in which it has been found.

α-PPP is illegal in the UK under the blanket ban on substituted cathinones, and due to its structural similarity to illegal drugs such as methcathinone

Methcathinone

Methcathinone , is a psychoactive stimulant, sometimes used as a recreational drug and considered addictive. It is usually snorted, but can be smoked, injected, or taken orally...

 and pyrovalerone

Pyrovalerone

Pyrovalerone is a psychoactive drug with stimulant effects via acting as a norepinephrine-dopamine reuptake inhibitor , and is used for the clinical treatment of chronic fatigue or lethargy and as an anorectic or appetite suppressant for weight loss purposes...

 it might be considered a controlled substance analogue in some countries such as the USA, Australia and New Zealand.