Hardcore drugs P, cocaine and Ecstasy gave New Zealand a bill of about $546 million for social costs in one financial year.
They are a big part of the total $1.3 billion that drug use cost the country in 2005 and 2006.
The figures come from a new index designed by economists to help police decide where drugs do the most harm and enable them to use resources more efficiently.
The Drug Harm Index, released yesterday, will help police determine the socio-economic costs from drug seizures and track the value of the drug trade in New Zealand.
It measures social harms related to drug use such as lost work output, health service use, diverted resources and reduced quality or loss of life.
The study investigated harm caused by four drug categories - stimulants (methamphetamine or "P", cocaine and Ecstasy), opioids (opium, homebake heroin and morphine), cannabis (plants and plant extracts) and LSD (hallucinogens).
It found that 373,310 people used cannabis, but only 17 per cent of these were frequent users.
There were 38,390 cocaine users, of which 88 per cent were frequent users.
Nearly 23,000 people used crystal methamphetamine (36 per cent of them often) and 81,890 took Ecstasy (24 per cent often).
Cannabis was the most used drug by far. At the other end of the scale, LSD use was limited to 2.6 times a year on average.
Men who took drugs were absent from work about 70 per cent more days than abstainers, and women 20 per cent more days.
Male cannabis users took about 8 per cent more sick days than the average male worker and opioid users took 40 per cent more days.
Other findings were:
* Cannabis cost $431 million, opioids $326 million and LSD $7.1 million.
* The most damaging drug per kilogram was LSD, which cost more than $1.05 billion a kg
* About 1578 people - 16 per cent of the prison population - were in jail as a result of drug-related crimes. This was at a cost of about $68,880 per person - $108.7 million in total.* Court costs were $353 million.* People serving community sentences cost $20.9 million and those on home detention cost $300,000.* Hospital costs attributed to patients with drug-related problems amounted to $6.76 million - an average of about $2949 for each of 2292 patients.* There were about 1920 drug-related deaths (including road accidents and homicides), costing $205.2 million, or $106,000 a person
While stimulants contributed 41 per cent of the total costs, figures showed that in 2006, police and Customs seized 33,480kg of cannabis compared with only 155kg of stimulants.
And police dealing with drug offences spent 55.8 per cent of their time addressing cannabis, against 43 per cent of their hours dealing with stimulant-related issues.
Former police detective Mike Sabin, who now specialises in dealing with P users, said police should dedicate as many resources to drug offences as they did to road policing.
He said police and the Government had made an effort to reduce road accidents over the past 10 years.
"We've seen a halving of the road toll in that time ...
"If we saw the same level of policing on drugs I think we'd see a significant reduction in the costs identified in this report."
Police had started to steer away from drug and organised crime policing, possibly because it was costing too much, clogged up the courts and created statistics that would not exist unless you "went out and found the drugs", Mr Sabin said.
Police spent about 4 per cent of their time working on drug-related offences, the index showed.
National crime manager Detective Superintendent Win van der Velde told the police Ten One magazine a reduction in social costs since 2000 showed drug seizures in 2006 avoided $485 million of drug harm.
"This index holds the potential for police to become more targeted and responsive to areas of crime where greater harm occurs."
The study did not include party pills such as benzylpiperazine (BZPs), which were reclassified as Class C drugs from April 1.