The first rule of taking sleeping pills is don't drink alcohol, says a sleep specialist who has helped courts understand the bizarre behaviour caused by the risky cocktail.

Even the information handed out by pharmacists with common prescription sleeping pills such as zopiclone contains clear written warnings against using them with alcohol.

The official datasheets give much sterner warnings against the practice — which the Rugby Union has said All Blacks Israel Dagg and Cory Jane engaged in on a night out during the 2011 World Cup.

Jane said this week there was "no mixing with energy drinks" after the pair took sleeping pills and there had been "no thought of going out to the pub drinking".


He has no recollection of the night out, during which they were seen behaving oddly in Takapuna.

Claims of sleeping pill use with energy drink Red Bull by league players in Australia date back to 2009.

This month New Zealand Warriors doctor John Mayhew told ABC News the mixing of sleeping pills, alcohol and energy drinks was widespread in the NRL and was a problem in other codes too.

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Doctors say there are clearly legitimate uses for sleeping pills by top sportsmen and women, such as when they fly between time zones and then have to perform.

But Dr Tony Fernando, an Auckland University psychiatrist and sleep specialist said sports players - and everyone else - should cork the liquor bottle well before popping the pills, although he could offer no guidance on the time gap required.

Zopiclone and the related benzodiazepine class of sleep medications all worked on the same receptors in the brain. Alcohol and benzodiazepine-like drugs worked on the GABA neurotransmitter system. Taking the two together exaggerated the effects.

"It can increase the sedation, it can cause loss of consciousness or even bizarre behaviours when you mix with alcohol. You are tweaking a system and adding an extra push from alcohol. You just don't know how the brain will respond."

Dr Fernando described a case — for which he gave expert evidence — in which a man was acquitted of charges related to sleep-driving.

"He has been taking sleep medication for a long time and was not a big drinker. He had lots of alcohol one night with sleep medication and ended up doing extensive sleep-driving.

"They're not fully conscious. It's no different from sleep-walkers. They can do automatic things like walk, even cook, have sex. I have treated a few for sleep-sex."

The leaflet written for patients taking the Imovane brand of zopiclone warns it can cause sleep-walking and says alcohol "can increase the risk of sleep-walking or other behaviours such as driving or eating food whilst asleep. The risk is increased if you take more than the recommended dose.