Cold Medicine Safe While Breastfeeding

No. I would not use nyquil or dayquil. Call the nurse at your doctor's office. If I remember right, my doctor told me that I could take the children's formula of cold medicine... But that was 2 yrs ago and before they pulled all the OTC cold medicines for children under 6. Now, they have much more restrictive guidelines due to the risk of cold medicine on small children and infants.

Of course, if you feel you must take some adult strength decongestant, then rely on frozen breastmilk and pump & dump while on the medicine plus several days after you stop.

By the way... I'd still rely on my dr's advice however, in case this helps, here is a link to a site that says what you should avoid when sick (Nyquil is specifically a no, see below):
http://breastfeedingbasics.com/html/when_moms.shtml

For coughs:
Avoid products with an alcohol content of over 20%. Benylin, Robitussin (DM, PE, and Maximum Strength), Triaminic Expectorant, and Vicks 44E and Vicks 44 Dry Hacking Cough are not harmful, but watch for infant drowsiness. Avoid multi-action formulas such as Tylenol Multi-Symptom Cough medication and Vicks Nyquil Liquid or Liquicaps.

I know Tylenol was always safe but my last baby is now 8 so I don't know if things have changed. I think it's always best to seek advice from you doctor. I remember taking meds in between feedings so that most of the effect could be gone by the next feeding.

I was told just plain tylenol or sudafed, though sudafed might have a slight but temporary drying effect (on milk supply).

I've found www.kellymom.com a good source of breastfeeding info.

here is a good site to reference:
http://www.breastfeedingonline.com/meds.shtml
this article in particular, go about half-way down and you will see a list of different types of medications and how they affect the baby:
http://www.medsafe.govt.nz/Profs/PUarticles/lactation.htm
looks like they have many other articles as well that might be of use to you =)