Molecular dynamics simulations of the drug-resistant M2 mutants, A30T, S31N, and L26I, were carried out to investigate the inhibition of M2 activity using amantadine (AMT). The closed and open channel conformations were examined via non- and triply protonated H37. For the nonprotonated state, these mutants exhibited zero water density in the conducting region, and AMT was still bound to the channel pore. Thus, water transport is totally suppressed, similar to the wild-type channel. In contrast, the triply protonated states of the mutants exhibited a different water density and AMT position. A30T and L26I both have a greater water density compared to the wild-type M2, while for the A30T system, AMT is no longer inside the pore. Hydrogen bonding between AMT and H37 crucial for the bioactivity is entirely lost in the open conformation. The elimination of this important interaction of these mutations is responsible for the lost of AMT's function in influenza A M2. This is different for the S31N mutant in which AMT was observed to locate at the pore opening region and bond with V27 instead of S31.