Medsafe has ordered the immediate recall of a number of erectile dysfunction formulas and is advising consumers to stop taking the products because of significant health risks.
The medicines safety authority has ordered the recall of SZM Formula for Men, Stallion, Volcanic and Tomcat Ali.
The products are sold in health food stores and pharmacies, as well as adult shops and over the internet.
Director-General of Health Stephen McKernan says tests have shown the products contain an undeclared prescription medicine Tadalafil - a compound marketed at Cialis.
Tadalafil is known to interfere with some heart medications and can be harmful, even fatal, in some people.
Mr McKernan says it appears that there is a new approach to tampering with the products, by adding inferior products to the capsule shell rather than to the contents. He says that practice may not be confined to just those four products.
The distributor of Volcanic says he had no idea that the pills were harmful to people's health.
John Vaughn, of Melric International, says the Volcanic pills were submitted for testing and approved for distribution in New Zealand. He says it appears the Tadalafil was contained in the pill casing, and not as part of the formula.