To cite the R package 'dlnm' in publications use:

Gasparrini A (2011). “Distributed lag linear and non-linear models in R: the package dlnm.” Journal of Statistical Software, 43(8), 1–20. https://www.jstatsoft.org/v43/i08/.

A BibTeX entry for LaTeX users is returned by: toBibtex(citation('dlnm'))

Corresponding BibTeX entry:

  @Article{,
    title = {Distributed lag linear and non-linear models in {R}: the
      package {dlnm}},
    author = {A. Gasparrini},
    journal = {Journal of Statistical Software},
    year = {2011},
    volume = {43},
    number = {8},
    pages = {1--20},
    url = {https://www.jstatsoft.org/v43/i08/},
  }