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Fears about the long-term legacy of New Zealand's P epidemic have promoted a decision to extend a study into "meth babies" so the infants are monitored until they are at least 3.
Early data from the joint NZ-US study has already shown the babies are 3.5 times more likely than others to be born below average weight.
Methamphetamine is known to cross the placenta to the unborn child and complications can include increased rates of premature delivery, growth retardation and effects on the central nervous system.
Some babies face spending their first few days of life being weaned off a drug they are born dependent on.
Dr Trecia Wouldes, who is leading the study, said she had seen "chaotic cases" in the six years since methamphetamine exploded on to the scene, claiming lives, fuelling violent crime and decimating families.
Concern was now turning to a new generation of victims - the babies of P-using mothers, and children who live under the cloud of the drug.
"We are going to see some seriously affected children because of the combination of drugs and other factors such as poor nutrition and backgrounds of domestic violence, which will affect early development. They are a high risk group."
The study is part of international research at five other centres with major P problems - Honolulu, Hawaii, LA, Iowa and Oklahoma.
The New Zealand arm of the research is costing almost $2 million, with funding from the Child Health Research Foundation, the Auckland Medical Research Foundation and the United States Institute of Drugs.
It tests babies at birth, one month, three months, nine months and one year. The extra funding will allow researchers to continue testing at two years and three years.
Dr Wouldes, from the University of Auckland School of Medical and Health Sciences and an expert in babies born to drug-using mothers, said it would be at least 18 months before more was known about the damage that might have been done.
Sixty mothers and babies are involved in the NZ part of the study and Dr Wouldes hopes for 120.
They range from women who dabbled with P, those who smoked it a lot and those who have a history of addiction to various drugs.
A further 60 mothers and babies - including 1-year-old Gemma McGill - are in a control group as part of the study.
Dr Wouldes said children born to women who dabbled with P but quit were likely to be fine, but "we really don't know that yet and I say it very, very cautiously".
The biggest concern was the mothers with a history of dependence who had switched to using P, and the environment those children were likely to be raised in during their most formative years.
"We don't know what it's going to mean for children who have that exposure, then go into a sub-optimal environment," Dr Wouldes said.
"They can become at risk of all sorts of things later in life."
Dr Chris Wilkins, leader of Massey University's annual Illicit Drug Monitoring System study, said his latest research found that more than three-quarters of P users admitted to mood swings and short temper, while about the same number said it caused problems in their relationships.
More than a third of them admitted to violent behaviour.
And the country is seeing a shift from P being a drug used across all sections of society to one used by an increasingly lower socio-economic group, as middle-class users have been put off by the high-profile violence sparked by the drug. Meanwhile, police figures show children are found at one in three clandestine P labs.
Dr Wouldes said her research aimed to discover what impact these elements combined were having on children. "Children who are born to drug users are the highest risk of developmental adversity."
