DF Concerts, organisers of Scotland's biggest music festival, said legal or herbal highs would not be permitted on site this weekend.
A statement said: "Selling these substances is prohibited and anyone found with these substances in their possession will have them immediately confiscated.
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"Legal does not mean safe and that these substances can cause serious harm especially when mixed with others such as alcohol.
"The terms legal high and herbal high are often misleading as many of these substances are not meant for human consumption and can kill."
The Scottish Government announced last month that an expert group is to be set up to look at ways of tackling the sale and supply of legal highs.
The substances are produced to provide a similar effect to drugs such as Ecstasy and are often labelled and sold as plant food or bath salts, or marked as not fit for human consumption, as a tactic to avoid the law.
Between 2009 and 2012, legal highs were implicated in at least 73 deaths in Scotland.
Balado airfield in Kinross-shire will host T in the Park for the last time this year after safety concerns forced organisers to look for a new site.
About 85,000 revellers are expected to watch performances by the likes of Arctic Monkeys, Calvin Harris and Biffy Clyro from July 11 to July 13.
Festival-goers have been reminded to plan their journey ahead of time and pack appropriate clothing, footwear and medication.
Geoff Ellis from DF Concerts said: "It's going to be a momentous festival weekend. We have an incredible line-up and we'll be saying bye to Balado after 18 years, which means it'll be a finale party to remember.
"However, we want to make sure everyone comes prepared to enjoy the entire weekend so we recommend that they heed the tips from our partners before setting off."