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Christopher McGuire saved himself just £7 by placing strips of an anti-psychotic drug in empty packets of the painkiller and swapping them for new packets at 4 south London pharmacies.
But he cost the manufacturers £2.4 million when they were forced to recall the product.
The court has heard how McGuire's scheme involved asking for Nurofen Plus at a pharmacy counter and then attempting to pay for it with a card he knew would be declined.
When the pharmacist was distracted he would discreetly swap the contaminated packet for the fresh one and walk away.
McGuire took 32 tablets of the drug each day to feed his secret addiction, but after losing his job he struggled to pay for it.
Instead, the 31-year-old replaced empty packets with the Seroquel he was being prescribed for schizophrenia, and the contaminated packs ended up in the hands of unsuspecting members of the public.
Two men, Peter Letham and Paul Connor, took the anti-psychotic drugs in error, believing them to be Nurofen Plus, and were left feeling unwell.
On July 24 and July 28 last year two other consumers realised the Nurofen Plus they had bought also contained Seroquel instead, but did not swallow any.