The fatalities happened between 18 June last year and 6 February this year and the coroner described their effects as "catastrophic".
Coroner Suzanne Anderson told a court in Belfast: "It does seem that there has been a cluster of deaths involving this particular drug."
An inquest was held into one of the deaths on Thursday.
Brian Mills, 41, a postman from Shore Road in Kircubbin, Co Down, complained to his son James that he was too warm following an all-night drinking session at his home.
Minutes later he stopped breathing, appearing to be having a fit, James Mills told the inquest.
Paramedics were unable to save him.
Dr Bernadette Prentice, a scientist from Forensic Science Northern Ireland (FSNI), analysed the victim's blood for toxins and found 4,4-Dimethylaminorex, known as speckled hen or speckled cross.
A total of 287 tablets containing the drug were discovered at Mr Mills' home by his brother, Leonard.
Dr James Lyness, assistant state pathologist in Northern Ireland, examined his body and said Mr Mills' death was one of several involving the drug.
He told the inquest: "There are 19 cases from 18 June 2013 to 6 February 2014 where the 4,4-Dimethylaminorex... is mentioned within the cause of death."
Dr Prentice said the drug was not controlled (banned by legislation) in the UK.
She added: "4,4-Dimethylaminorex can be regarded as a novel psychoactive substance.
"It has rarely been encountered as a drug of abuse and consequently [there is] very little data."
She said it could be sold as powder or tablets and was first found in the Netherlands in 2012 and later in Finland, Hungary and Denmark.
The message is clear: any substance, whether illicit like ecstasy, prescription drugs that have not been prescribed for you, or so called legal highs, can pose a real, potentially fatal risk to your health and wellbeing. The only safe advice is not to use them. This also applies to buying substances from the internet.
Health Minister Edwin Poots
Police made several seizures of the substance in Northern Ireland last year and the Police Service of Northern Ireland's organised crime anti-drugs unit is investigating, Dr Prentice told the inquest.
She said a certified reference standard for testing was not available but there was little reason to doubt the accuracy of the results.
"It is clear that they will have some similarities to related stimulant drugs."
Among its potential effects are agitation, increased body temperature, convulsions, organ failure and death.
Other stimulant drugs, taken in Mr Mills' case, were likely to further increase the toxicity of 4,4-Dimethylaminorex, the inquest was told.
The coroner observed: "It seems to have had catastrophic effects from the outcome of our hearings in these inquests."
Dr Prentice said police had been holding meetings with forensic scientists and the pathologist's department.
Meanwhile, the PSNI has confirmed that a senior detective is co-ordinating the investigations into the drug-related deaths.
Detective Superintendent Andrea McMullan, from the PSNI's Organised Crime Branch, has met with the Coroner, the State Pathologist and officials at the Department of Health, Forensic Science NI and other agencies as part of her role.
Anyone who takes illegal drugs runs a serious risk of causing themselves serious harm or killing themselves. There is no safe illegal drug.
DS Andrea McMullan
She said: "The substance is para-methyl-4-methylaminorex and is not confined to one particular brand of tablet. It has been identified in a number of tablets and in a number of deaths.
"People should not lull themselves into a false sense of security by thinking if they avoid tablet X and only take tablet Y or Z they'll be ok. The tragic reality is they will not."
Police investigations into drugs-related deaths last summer resulted in a total of 11 arrests.
One person has appeared in court. Three others were awaiting court proceedings but one has since died.
The PSNI statement said that work has also been done to identify the supply chain of the drugs concerned to look at any linkages between the deaths - including those involved supply, distribution and manufacture.
Detective Superintendent McMullan said that the drugs problem cannot be solved by police alone.
"That is why we are working closely with experts and officials in the fields of health, education, forensic science and the criminal justice system.
"We want to ensure that we are doing everything possible to prevent the supply of drugs and arrest those involved but at the same time make people aware of the real dangers they face to their health and their lives if they take illegal or controlled drugs," she added.
Anyone with any information about the supply of controlled drugs can contact police on 101..