A police force is to replace CS gas with another spray containing a chemical which mimics the heat effect of natural chilli peppers.
Hertfordshire Police will issue the new Pelargonic Acid Vanillyamide (PAVA) spray to its officers on Wednesday.
PAVA does not affect people nearby when it is used and there is no need to decontaminate the area in which it is used, Herts Police said.
The spray is usually aimed at the eyes of a suspect.
Ch Insp Steve Kissane, who has co-ordinated the spray's introduction, said: "The new spray has been proven to be effective in a greater number of cases than CS during trials... mainly because it is an inflammatory agent.
"It does not rely on pain alone to cause incapacitation.
"This is significant as, in the vast majority of instances where officers need to use an incapacitant, the person being sprayed is under the influence of drink or drugs and has an artificially high tolerance to pain."
PAVA has no long-term medical effects and in most cases, people sprayed make a full recovery within 45 minutes.
CS gas was introduced in 1996 across England and Wales.
It stuns its victims, causing streaming eyes and nostrils and sometimes breathing difficulties.