Aidan Hamilton and Robert Strang died after apparently ingesting kratom product last month

Federal authorities investigating the recent deaths of two University of Mississippi students have charged a store clerk and his son with selling an illegal kratom product, prosecutors announced on Friday.

A drug taskforce in Mississippi had previously urged people to avoid kratom, an herbal substance that acts as a stimulant at low doses and a sedative at high doses, after authorities found packages of kratom derivatives while investigating the deaths on 21 September.