At least eight people in four states have fallen ill after eating Diamond Shruumz-brand Microdosing Chocolate Bars, including several who had seizures or lost consciousness and needed to be placed on ventilators. People also developed high blood pressure and abnormal heart rates.

The Food and Drug Administration has warned people against consuming the bars, which are sold online and in smoke shops across the country and come in flavors like birthday cake and cookies and cream.

It’s not clear why the bars might have sickened consumers. Diamond Shruumz has marketed the chocolates as “trippy little squares” and calls the chocolate a “microdose,” referring to a term for a small amount of a psychedelic. But the company has said the bars do not contain psychedelic substances, including psilocybin, the hallucinogenic drug found in so-called magic mushrooms. Instead, Diamond Shruumz says its products have “nootropic and functional mushrooms,” like Lion’s Mane, Reishi and Chaga mushrooms.

The company did not respond to multiple requests for comment.

The Food and Drug Administration and Centers for Disease Control and Prevention are working with poison control centers and state health agencies to investigate the cause of the illnesses.

“Our initial belief is that it’s something else that truly isn’t psilocybin but close enough to give that effect, which is why it’s being marketed as a microdosing edible,” said Dr. Steven Dudley, director of the Arizona Poison and Drug Information Center.

Mushroom chocolates have grown more popular in recent years, as companies capitalize on a wealth of research around — and consumer interest in — psilocybin. “There’s just this real proliferation of these kinds of products,” said Dr. Stacy Fischer, a researcher studying psilocybin at the University of Colorado School of Medicine.