A Wisconsin couple have been charged with plotting to stalk and poison two women whom the man had previously dated, using cyanide, homemade poisons and other substances, the authorities said.

The couple, Paul VanDuyne Jr., 43, and Andrea Whitaker, 41, both of Madison, Wis., were charged with attempted murder, stalking, aggravated battery and recklessly endangering safety, the Wisconsin Department of Justice and the Police Department in Middleton, Wis., said in a statement on Friday.

According to court documents, Rock County sheriff’s deputies were dispatched to a hospital on May 12 to investigate a possible poisoning.

Over the next five weeks, they conducted an investigation with the F.B.I. and other agencies and found that Mr. VanDuyne and Ms. Whitaker had “conspired to gather or create elaborate poisons” in an attempt to kill two women, court records show.

One of the women began noticing the effects of a poisoning attempt on or about April 26, when the authorities say she noticed that a water bottle in her gym bag had a “rancid” taste. The water caused the victim, who was not identified in court records, to throw up. In a separate incident in June, she was hospitalized for severe abdominal pain. Doctors found a large amount of thallium in her system, according to court documents.

Investigators found that the woman’s car had been broken into, and that her gym water bottle was laced with thallium and cyanide, the authorities said. Thallium, which was once used in rodent poisons, is a “tasteless and odorless” substance that has been used in murders because it is difficult to detect, according to the Centers for Disease Control and Prevention