A 2009 study by the U.S. Department of Justice among its 5 component agencies showed that of all the non-lethal weapons available to law enforcement, only two are commonly used by all the 5 agencies under the department: the baton and the pepper spray.
The pepper spray and the baton are used by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), the Federal Bureau of Prisons (BOP), the Drug Enforcement Agency (DEA), the Federal Bureau of Investigation (FBI) and the U.S. Marshals Service (USMS).
These agencies' common preference for the baton and the pepper spray is an open endorsement to their effectiveness as non-lethal or less-lethal weapons
An attacker who gets pepper-sprayed will immediately feel extreme irritation in areas where the Oleoresin Capsicum compound gets in contact with – this is usually the skin, eyes, mouth, face and throat. The effect is powerful and just long enough for the victim to escape from the attacker or for a law enforcement officer to manage control over a subject.
One reason why pepper spray is very popular among police and civilians is that it leaves no lasting effects on the target person. The effect is temporary and eventually wears off making it a safer choice compared to other non-lethal or less-lethal weapons.