Doctors in San Diego had quite a weekend after they treated 16 patients who had overdosed on a synthetic drug known as spice. According to a report from the San Diego Union Tribune, the incidents marked the second weekend in a row where multiple people needed treatment for acute intoxication after smoking the drug.

Police have begun investigating the potential source of the synthetic marijuana product, which remains illegal in the state of California. Many consumers turn to products like spice believing that they are a safer alternative to actual cannabis. Despite its status in California, the drug is available for purchase in gas stations and corner stores in states across the country.

The majority of the patients in the recent string of overdose cases were in their late teens and early twenties, but one patient was reportedly as young as 13. Three of the patients were in serious condition, San Diego Fire-Rescue Department spokesman Lee Swanson said.

The symptoms of a spice overdose can range from mild nausea, increased heart rate and agitation to trouble breathing and loss of consciousness. None of the recent cases were life threatening, Swanson said.

One of the patients was discovered near the San Diego Central Library on Park Boulevard and another was found nearby, but the majority of the patients were found near the trolley station at 12^th and Imperial.

Synthetic cannabis is notorious for leading to episodes where people who take the drug require medical attention. As it grows in popularity, medical professionals are increasingly worried about the long-term impacts of spice use, which have gone largely unstudied to this point.