The vast majority of elite-level rugby union players diagnosed with a concussion will not be able to return to play for 12 days as a result of changes being introduced by the sport's world governing body from July 1.
World Rugby is following recommendations by an independent Concussion Working Group following a review of the latest scientific evidence.
The current regulations allow players who fail a head injury assessment during a game to be back on the field seven days later if they follow return-to-play protocols.
While that could still be the case for some, provided they get the approval of an independent concussion consultant, the majority will be out of the game for five more days.
The updated criteria being used to judge how quickly players can return after showing obvious concussion symptoms now includes their history of concussions.
The new criteria will be in place for next month's Test series that feature match ups including England v the Wallabies in Australia and Ireland v the All Blacks in New Zealand.
World Rugby's chief medical officer Dr Eanna Falvey said: "It is going to be a new mindset for coaches and players.
"Our approach means it is now overwhelmingly likely a player diagnosed with a concussion won't play in their team's next match.
"World Rugby firmly believes that scientific evidence supports our protocols, but we are continually monitoring and testing them to ensure that they are fit for the modern game..
"We recognise that there are differences in concussion symptoms and concussion history, and this process enables us to further protect elite players by individualising their rehabilitation.
"It also keeps in place all the benefits of the previous protocols, which have been so successful in beginning to tackle under-reporting of symptoms which evidence shows that, while improving, remains an issue."
World Rugby chief executive Alan Gilpin added: "There are always going to be head impacts and there are always going to be concussions in rugby, so we are never going to eradicate that with the nature of the sport we have.
"But we want people comfortable that we have got a game that is safe to play at all levels and the sport is doing its best to protect and look after players' safety and welfare.
"We are making progress, there are lots of areas where we have advanced. You can never do too much in this area."