[1] Common side effects include nausea, diarrhea, headaches, feeling tired, and cough.

[12] In HIV, high level resistance is associated with the M184V/I mutation in the reverse transcriptase gene as reported by Raymond Schinazi's group at Emory University.

GlaxoSmithKline claimed that the M184V mutation reduces "viral fitness", because of the finding that continued lamivudine treatment causes the HIV viral load to rebound but at a much lower level, and that withdrawal of lamivudine results in a higher viral load rebound with rapid loss of the M184V mutation; GSK therefore argued that there may be benefit in continuing lamivudine treatment even in the presence of high level resistance, because the resistant virus is "less fit".

The HBV reverse transcriptase gene is 344 amino acids long and occupies codons 349 to 692 on the viral genome.

[14] The change in amino acid sequence from YMDD to YIDD results in a 3.2 fold reduction in the error rate of the reverse transcriptase, which correlates with a significant growth disadvantage of the virus.

They inhibit the HIV reverse transcriptase enzyme competitively and act as a chain terminator of DNA synthesis.

Lamivudine showed no evidence of carcinogenicity or mutagenicity in in vivo studies in mice and rats at doses from 10 to 58 times those used in humans.

[16] When used in combination with AZT, he discovered that lamivudine's negative form reduced side effects and increased the drug's efficiency at inhibiting reverse transcriptase.

[17] The combination of lamivudine and AZT increased the efficiency at inhibiting an enzyme HIV uses to reproduce its genetic material.