All of the following are true about opioids except?

Nalmefene is a derivative of Naltrexone and is orally effective and longer acting. Naltrexone, is a medication primarily used to manage alcohol or opioid dependence. An opioid-dependent person should not receive naltrexone before detoxification. It is taken by mouth or by injection into a muscle. Effects begin within 30 minutes. All the other statements are true. Ref: KD Tripathi 8th ed.