Switzerland's largest techno party, the Zurich Street Parade, takes place on Saturday, with about a million people expected to participate.
Partygoers are being advised not to buy refreshments from unofficial sources after problems with spiked drinks at other festivals this summer.
Several people needed medical treatment in hospital at last month's Geneva Lake Parade after unintentionally consuming liquid ecstasy (GHB).
The victims complained that drinks they had bought from the street had been spiked with the drug that causes drowsiness and disorientation, and can have life threatening side effects if taken in high doses or mixed with alcohol.
Zurich Street Party organisers are urging people only to buy unopened drinks from official stands, a message repeated by the Swiss Institute for the Prevention of Drug and Alcohol Abuse who will again operate a special ecstasy hotline to provide drugs information.
Street Parade spokesman Stefan Epli explained that this year's slogan, "Today is Tomorrow", promotes tolerance and calls on people to be aware of the twin threat of drugs and Aids/HIV.
"Everyone is responsible for themselves. If you take something then know what it is you are taking," he told swissinfo. "And above all else, don't take drinks from someone you don't know, but take a closed bottle from us."
"Don't fall victim to the popular cliché that you need drugs to party. Never mix GHB with alcohol (even small doses!). The best thing to do is keep away from party drugs altogether," the Street Parade official website added.
Less of a threat in Zurich
The drugs advisory body Streetwork Zurich will have an information stand at Bürkliplatz next to the lakeside with volunteers on the streets distributing 50,000 flyers. They will also test drugs to inform people about their possible side effects.
"It is difficult to say if we will have the same problems at Zurich as they had in Geneva," said Streetwork spokesman Alexander Bücheli.
"There is a bigger tradition of GHB consumption in Zurich than in Geneva, where it has only appeared in the last couple of years. If people take a drug without knowing very much about it then they might take too much or mix it with alcohol, and that causes problems.
"It is always possible that people can sell drugs and say they are something else, but I don’t think it will be the same trouble in Zurich."
Gerhard Lips, police chief of Zurich city’s eastern region, also played down the GHB threat after consulting with colleagues in Geneva.
Big crowds expected
"I don't think there will be a special problem with these drugs at the Street Parade," he told swissinfo. "It has not been a big issue in our planning and we have added no special measures."
The first Street Parade in 1992 attracted 1,500 people, but organisers expect the same attendance for the 14th parade on Saturday as last year when one million revellers flocked to the streets of Zurich.
The parade will feature the colourful lovemobiles from around the world and a feast of dance music into the early hours of Sunday.
"It was never important for us to have the biggest parade, but we wanted it to be the most beautiful," said Stefan Epli. "I think we have succeeded in that respect."
The Zurich city authorities said they would set up the biggest professional rescue organisation in Switzerland for the event, providing first aid centres, tents and showers.
The emergency services team includes paramedics, medical volunteers, and doctors, as well as firefighters and fire safety officers.
For late night revellers, the Federal Railways has introduced a new SMS service to help travellers beat the queues at the ticket machines.
swissinfo, Matthew Allen in Zurich
The 14th Street Parade is expected to attract one million people. The first parade in 1992 saw 1,500 revellers attend.
The Street Parade association has a budget of SFr1.2 million ($960,000).
The organisers say that 32 "fabulous" love mobiles will surprise and delight ravers with their creative decorations and the latest electronic sounds.
The Swiss Federal Railways has laid on 130 extra trains which will run until the early hours of Sunday morning.