The number of New Yorkers who die of cocaine overdose appears to go up when the temperature surpasses 75 degrees, a new study suggests.

The findings, reported in the journal Addiction, suggest that relatively hot days may increase cocaine users’ vulnerability to the drug’s potentially fatal effects.

For the study, researchers analyzed data on deaths and weather for New York City for the years 1990 through 2006. They found that for every 2-degree increase in average temperature beyond 75 degrees, there were 0.25 additional cocaine-overdose deaths per 1 million residents each week.

Applied to New York, that would mean an extra two deaths per week, said lead researcher Dr. Amy Bohnert, a research fellow with the University of Michigan Medical School and the Ann Arbor VA.

Cocaine is known to raise a person’s core body temperature, Bohnert explained in an interview, and when people are on the drug, they are less likely to take steps to cool themselves down on a hot day. The resulting hyperthermia may make people more vulnerable to overdose at relatively lower blood-cocaine levels.

Using data from the New York City medical examiner, Bohnert and her colleagues found that between 1990 and 2006, an average of 16 people died each week from an accidental drug overdose - with a range of anywhere from 3 to 48 deaths per week.

Cocaine - alone or along with other drugs - was behind more than half of those deaths.

Bohnert’s team found that hotter days were related to an increase in deaths from cocaine, but not to deaths from overdoses of opiates, such as heroin. Past research has suggested that opiates have a more complex effect on body temperature - both raising it and lowering it at different points, Bohnert explained.

Few of the deaths in the study involved neither cocaine nor opiates, so it was not possible to study the relationship between temperature and overdoses from amphetamines or other stimulants, according to Bohnert.

The bottom line, according to Bohnert, is that cocaine users should be aware of the potentially greater risks they face on hotter days. Ideally, they should stop using the drug altogether, the researcher noted - and the current findings, she said, might serve as a reminder that cocaine is a dangerous drug.

Bohnert also pointed out that each year, New York City sees about seven weeks with average temperatures of 75 degrees or higher.

“That is not an extreme temperature. So we’re not just talking about a risk during heat waves,” she said.

According to Bohnert, it is likely that the effects of heat on cocaine-related deaths would be similar in other cities in the Northeastern U.S. In the South, though, it might take a higher “threshold” temperature to spur an increase in deaths, as people there are accustomed to consistently warm temperatures.

Bohnert added that large cities like New York would be expected to have more days with above-threshold temperatures compared with smaller cities and suburbs in the same region. Big cities tend to trap heat and cool off less overnight.

SOURCE: Addiction, online March 2, 2010.