戒毒 means 'to quit / kick a drug habit' and is a separable verb (离合词): the verb 戒 and the noun 毒 can split when inserting aspect markers, complements, or duration — e.g., 戒了毒 ('quit drugs'), 戒过毒 ('has quit drugs before'), 戒了一年的毒 ('quit drugs for a year'). You can also add a complement after 戒: 戒不掉 ('can't quit'). Be careful: 毒 here refers specifically to drugs (毒品), not poison (though 毒 can mean poison in other contexts). This word is commonly used in public health and rehabilitation contexts.