MedlinePlus: Guaifenesin
- Provides information on usage, precautions, side effects and brand names when available. Data provided by various government agencies and health-related organizations.
- http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a682494.html

Lufyllin
- Full prescribing information from RxList.
- http://www.rxlist.com/cgi/generic2/dyphylline.htm