Eating one of the world’s hottest chillies can cause five weeks of headaches, scientists have warned after a man was hospitalised.

The 34-year-old American patient required emergency treatment for excruciating headaches and neck pain after eating the “Carolina Reaper”, which is as strong as military-grade pepper spray.

A scan showed several arteries in his brain had temporarily narrowed, causing severe episodic "thunderclap" headaches.

Doctors warned that taking part in hot chilli contests could have unexpected consequences, as they published details of the incident in journal BMJ Case Reports.

Produced by The PuckerButt Pepper Company, the Carolina Reaper is the current Guinness World Record holder for the hottest chilli and has been known to reach 2.2 million on the Scoville Scale.

That means one drop of its oil would be detectable in 2.2 million drops of water.

A Jalapeno pepper typically rates between 2,500 to 5,000 units on the scale.

The patient, who has not been identified, immediately began dry heaving after sampling the chilli, the US authors said in the paper.

Over the following days, he developed "intense" neck pain and headaches, each of which lasted just a few seconds.

The pain was so severe that he sought emergency treatment and he was tested for multiple neurological conditions, the results of which all came back negative.