The FDA has not specified how much Flexeril is a lethal dose for humans, explains Drugs.com. The lethal dose of Flexeril in mice is 338 milligrams per kilogram. The FDA has determined the recommended dosing for most adults to be 5 milligrams or 10 milligrams up to three times daily.
Flexeril is a muscle relaxer that must be prescribed by a doctor and is used to relieve painful skeletal muscle spasms. The most common symptoms of an overdose of Flexeril are drowsiness and tachycardia or rapid heartbeat. Anyone suspected of an overdose of Flexeril should immediately be treated in a hospital setting to monitor their symptoms. Although Flexeril-related deaths are rare, potentially life threatening complications like cardiac arrest and seizure are possible, notes Drugs.com.