British police arrested a man on Friday after anti-psychotic and epilepsy drugs were placed in packets of the painkiller Nurofen Plus, Scotland Yard said.
The case of suspected sabotage last month led to the makers of Nurofen Plus, Reckitt Benckiser, recalling the painkillers in Britain and halting their distribution.
A spokesman for London's Metropolitan Police Service said the unnamed 30-year-old man had been arrested in Bromley in the south of the capital on "suspicion of contamination of goods".
"The man is currently being held for questioning at a south London police station," the spokesman told AFP.
Five contaminated packets of Nurofen Plus were found in Britain in August, prompting a national health warning and the recall by the manufacturers.
Four of the affected packs contained Seroquel XL, an anti-psychotic drug used to treat schizophrenia, mania and bipolar depression, and two people accidentally took the drug but suffered no harm.
The epilepsy drug Neurontin was found in another packet but no one was thought to have taken it.