Hyperpolarization-activated Cyclic Nucleotide-gated (HCN) channels are responsible for the functional hyperpolarization-activated current (I_h) in dorsal root ganglion (DRG) neurons, playing an important role in pain processing. We found that the known analgesic loperamide inhibited Ih channels in rat DRG neurons. Loperamide blocked I_h in a concentration dependent manner with an IC₅₀ = 4.9 ± 0.6 µM and 11.0 ± 0.5 µM for large and small diameter neurons, respectively. Loperamide-induced I_h inhibition was unrelated to the activation of opioid receptors and was reversible, voltage-dependent, use-independent, and was associated with a negative shift of V_1/2 for I_h steady-state activation. Loperamide block of I_h was voltage-dependent gradually decreasing at more hyperpolarized membrane voltages from 89% at -60 mV to 4% at -120 mV in the presence of 3.7 µM loperamide. The voltage sensitivity of block can be explained by a loperamide-induced shift in the steady-state activation of I_h. Inclusion of 10 µM loperamide into the recording pipette did not affect I_h voltage for half-maximal activation, activation kinetics and the peak current amplitude while concurrent application of equimolar external loperamide produced a rapid, reversible I_h inhibition. The observed loperamide-induced I_h inhibition was not due to the activation of peripheral opioid receptors since the broad-spectrum opioid receptor antagonist naloxone did not reverse I_h inhibition. Therefore we suggest that loperamide inhibits I_h by direct binding to the extracellular region of the channel. Since I_h channels are involved in pain processing, loperamide-induced inhibition of Ih channels could provide an additional molecular mechanism for its analgesic action.