Campers at Glastonbury Festival spotted taking legal highs including so-called laughing gas have been warned by local medics against using the mind-altering drugs.
The rushing sound of nitrous oxide being released in to balloons has been heard across the camp sites and music arenas while the ground is littered with the empty canisters.
A man was thrown out of the VIP hospitality area after being spotted passing around balloons.
Alongside the health risks associated with taking drugs, ambulance staff on site said it was concerned users could become unsteady on their feet and slip over in the muddy fields following lashings of heavy rain yesterday.
Glastonbury Festival organisers discourage the use of laughing gas and have been confiscating it when found in people's bags on arrival but the use of legal highs is not monitored by security staff.
Avon and Somerset Police said it would help organisers to "deliver on their policy".
A spokeswoman for the ambulance service said: "We warn against the use of any mind altering drugs, legal or otherwise, including laughing gas.
"They carry health risks and can have other repercussions such as making you unsteady on your feet and could cause you to slip over in the mud.
"We urge people at Glastonbury Festival to take care and stay safe."
Taking laughing gas through balloons is becoming an increasingly common sight at festivals across the UK.
Chief Inspector Mark Jackson said at the festival: "There is a zero tolerance policy towards illegal drugs.
"In terms of the other substances, that's something that the Glastonbury Festival has a view on.
"They have policies and we will certainly support them in delivering those policies.
"If we come across offences we will deal with them firmly and fairly.
"There may be a misapprehension that police at Glastonbury are soft on drugs but that isn't the case. We will deal with what we come across."