The westbound carriageway was shut between junctions 3 (Wesham Interchange) and 4 (Marton Interchange) at around 2.50am.
Police and traffic officers attended the scene and a diversion was put in place following the closure.
Officers have now confirmed they were responding to a “concern for safety call” involving a man.
The man was detained at around 5.20am and was taken to hospital for treatment, the force added.
Highways England have since confirmed the motorway has been reopened.
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“We are now in the process of re-opening the road following Lancashire Road Police advising us that it is safe to do so,” a spokesman said.
“Apologies for any inconvenience caused, we will advise again once fully open.”
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