Thomas Connor, of Trinity College Dublin, told the British Association science festival that laboratory studies had shown the drug, also known as MDMA, could suppress the immune system and, therefore, be a factor in increasing the risk of infection.
"There was a case report published this year of a young man in his 20s who presented with, basically, shingles of the eye. This is something that is extremely rare in young people. It is never seen unless somebody is very seriously immunocompromised, maybe an Aids patient etc.
"The striking thing, the only thing that could have been a predisposing factor, was that this person was a regular ecstasy user."
There have been two cases in which individuals developed meningitis soon after taking the drug, and three years ago a British survey of ecstasy users found a significant correlation between ecstasy use and self-reported incidence of infections.
"This research is in its early stage," Dr Connor said. "MDMA use has traditionally been associated with the dance club scene: a crowded environment where teenagers congregate. Such an environment is optimal for transmitting infection between individuals."
The drug can also induce hyperthermia, increase heart rate, blood pressure and anxiety levels. It has been linked with cardiac arrhythmia, renal failure, seizures and brain haemorrhage.
In the long term, ecstasy damages serotonin neurons in the brain. Such damage could last for years and predispose a drug user to depression, anxiety and impulsive behaviour, Dr Connor said.
It could also mean that Prozac and other antidepressants would be less helpful.