有效 (yǒu xiào) is the general word for 'effective' or 'valid' — it applies to methods, medicines, laws, and more. It is broader than 管用 (guǎn yòng, 'that works in practice') and more common than the formal verbs 奏效 (zòu xiào) and 见效 (jiàn xiào, 'to produce the desired result'). 生效 (shēng xiào) is specifically for laws/contracts 'taking effect'.