There are quite a few articles circulating around the internet in regards to using ‘guaifenesin' which is sold under names like Robitussin in pharmacies. The belief is that guaifenesin helps to loosen and improve mucus, however on discussion with several Australian pharmacists, they have consulted their drug guides and advised guaifenesin should not be used when trying to conceive right through to breastfeeding.
Guaifenesin is actually classed as a Category A drug in pregnancy and the pharmaceutical drug guide states that many women have used it during pregnancy with no obvious side effects, however it does say that there is no study on the amounts excreted in breastmilk – there is no proof either way if this can be harmful or not for baby.
On this basis, the pharmacists I contacted have recommended that using guaifenesin should be avoided when trying to conceive through to breastfeeding, as there is a risk there which may be slight, but not worth it. They also said it really is designed for the lungs and don't see how it can help with cervical mucus.
I asked BellyBelly's natural fertility expert, Sue Parsons from Fertile Mind and Body what her thoughts were on the use of Robitussin for cervical mucus and she said that it is fine, as long as it is only taken prior to the time of conception (i.e. before ovulation).
Like any medication or drugs, if you are trying to conceive, pregnant or breastfeeding, please ask your pharmacist first. Don't feel silly asking about the more common medications like cough medicine, pain killers or anti-inflammatories. Some of the more common medications can be just as unproductive or dangerous than the lesser common medications.