It causes immediate closing of the eyes and a burning sensation, difficulty breathing, runny nose and coughing.
The effects generally last about 30-45 minutes.
While the spray itself is not lethal, it can cause death in combination with medical conditions like asthma.
Last month, police pepper-sprayed people involved in a gang brawl outside the Whakatane courthouse.
In 2010, the Independent Police Conduct Authority found force used by four Whakatane police officers who beat Rawiri Falwasser, 26, with batons and pepper-sprayed him 65 times in a police cell in 2006 was "unnecessary, unreasonable, and unjustified".
The officers were charged with nine charges of assault but acquitted in 2008.
Mr Falwasser later received $30,000 in compensation.
Local police declined to comment on the Rotorua figures, referring questions to national headquarters.
A spokesman said pepper spray use fluctuated over time, and did not reflect local trends.
"Despite these fluctuations, crime nationally has been steadily dropping in recent years, as has the number of assaults on police."
This was partly due to increased access to a range of tactical options, including pepper spray, and training.
"Any police response is ultimately dictated by the actions and behaviour of those we are confronted with at the time, with OC spray just one of a number of potential options police may use."
Between March 2010 and June 2013, force was used in 0.2 per cent of face-to-face encounters.
Pepper spray was used in 32 per cent of these incidents.
As well as trialling more powerful OC spray and Tasers, police have also expanded their arsenal of non-lethal options to include a "sponge round" which can be fired from up to 35m away.
Police received regular training on pepper spray use, which focused heavily on sound judgment and good decision making "to resolve situations using the least amount of force possible, while maximising safety and minimising any risk to our staff, the subject and the public".
Any use of force must be lawful, justified, reasonable and proportionate to the circumstances, the spokesman said.
In the mid-1990s, the US Department of Justice cited nearly 70 fatalities linked to pepper spray use.
However, New Zealand Police Association president Greg O'Connor said pepper spray was a safer alternative to physical force and hugely effective as a deterrent for offenders.
"Most people who have been pepper-sprayed don't really want to be pepper-sprayed again."
It was also one of the best ways to avoid injury, he said.
"So many injuries are caused by flailing arms and knees while attempting to subdue someone who's going through some sort of psychotic episode."