A teenage girl who became hooked on methamphetamine, or "P", through her gang associations, says gangs are now lacing cheap cannabis deals or tinnies, with the drug. 

Crystal, 15, is recovering in foster care from a two-year P habit after running away from home and living with Auckland gang members who control the P industry.

She says young people who know enough about the drug to avoid it could still unwittingly find themselves smoking it through the cannabis spiking.

Crystal says she is afraid of what will happen when P-dealers she dobbed in get  out of prison. 

But she says she is more afraid of the drug itself, and that she would not be able to refuse it, if offered - even though it wrecked her health.

P has become an increasing problem in New Zealand over the last few years, with the drug linked to a series of violent crimes over the last year.

Side effects include irritability, insomnia, confusion, tremors, convulsions, anxiety, paranoia, and aggressiveness.

Steven Williams pleaded guilty to killing his stepdaughter Coral Burrows after a night of smoking P last year. The drug was also associated with Auckland multiple-murderers William Bell and Ese Falealii.