Cyclotraxin B, a cyclic peptide, is a highly potent and selective TrkB inhibitor without altering the binding of BDNF. Cyclotraxin B non-competitively inhibits BDNF-induced TrkB activity with an IC50  of  0.30 nM. Cyclotraxin B can crosse the blood-brain-barrier and has analgesic and anxiolytic-like behavioral effects.