Table 2.

Effects and mechanisms of different kinds of opioids on the immune function.

Opioids	Effect	Presumed mechanism of action
Morphine	+	Induces immunosuppression;23 decreases T-lymphocyte proliferation;24 suppresses Th-cell differentiation25
Fentanyl	+	Promotes the apoptosis in lymphocytes and macrophages26
Oxycodone	+	Suppresses the immune function27
Tramadol	−	Enhances NK lymphocyte activity; blocks tumor metastasis28
Buprenorphine	N	Devoid of any intrinsic immunosuppressive activity30
Sufentanil/alfentanil	+	Inhibits NK cells and suppresses mitogen-triggered lymphocyte multiplication29

“+”, pro-tumor; “−”, anti-tumor; “N”, no definite effects