Linked from
The 35 pages that link to Opioid, each with the reason it gives.
BuprenorphineNarrower topic: Buprenorphine is an opioid with a distinctive partial-agonist profile.
MethadoneNarrower topic: Methadone belongs to this broader drug class.
HeroinNarrower topic: Heroin belongs to this broader family of drugs.
DesomorphineNarrower topic: Desomorphine belongs to this broad drug class.