The incident comes after 15-year-old schoolboy Rio Andrew collapsed and died after he is suspected of drinking beer laced with ketamine at a rave party in Croydon earlier this month.
Police say they are still waiting for toxocology tests to determine his cause of death.
Earlier police at Glastonbury warned festival goers of the dangers of taking illegal drugs saying :“Ketamine and alcohol dangerously affect your heart and breathing. It can be deadly and you don't know what or how strong it is."
The festival, which features headline acts including Elbow, Metallica, Dolly Parton and Arcade Fire, opened officially today with a steady rain on the Somerset site.
An electrical storm on Friday evening led to the plug being pulled on the Pyramid Stage temporarily.
Lightning streaked through the sky while claps of thunder drowned out music as torrential rain hit festival-goers, leaving organisers saying it was unsafe to continue.
The weather problems led to Lily Allen's set being delayed by 45 minutes, while other stages also suffered setbacks.
Police said 85 crimes were reported within the first 48 hours and 30 people had been arrested but the figures were 30% down on last year.
Police said they used tracking software to locate one stolen phone and arrested a woman overnight.
Inspector Liz Hughes, of Avon and Somerset Police, said: "Thanks to a tracking app, we've been able to recover a stolen phone, which shows that they really do work.
"They are really useful and I would urge anyone who hasn't already got one installed to do so today.
"We've also arrested three men on suspicion of theft and this shows that there are a very small number of people who come here intending to steal and spoil the fun for everyone else.
"While the arrests are a positive step, it's a reminder to us all to look after your possession very carefully."
