The Ministry of Health issued the national warning Friday while also updating the death toll.
Of 34 people who have been poisoned, 14 men and five women, age 32 to 72, have died since the first week of June, the ministry said.
Authorities warned that it was not known how much alcohol had been adulterated, but have confiscated some 30,000 bottles and are carrying out a countrywide investigation.
The doctored alcohol contained between 30 to 50 percent methanol, according to Donald Corella, head of emergency services at Calderon Guardia Hospital in San Jose, who was quoted in the daily La Nacion.
He said six people who were treated at his hospital had died, while four others survived but suffered "very serious after-effects" ranging from irreversible total blindness to brain lesions that cause tremors similar to Parkinson's disease.
If ingested in large quantities, methanol can cause blindness, liver damage and death.
According to authorities, the majority of the 19 deaths occurred among homeless and alcoholic individuals.