Mercury in 6th House synastry promotes and governs relationships that are based on professional activities and a healthy lifestyle. Ideas and experience of the Mercurial personality encourage the Sixth House person to work more effectively (and efficiently) while taking better care of their health. This type of synastry favors common interests in such areas as business, human resources, and everything that has to do with sport and fitness. Another example of an effective relationship is the “doctor-patient” tandem, especially if the doctor’s synastry personality is that of Mercury.
All in all, Mercury in Sixth House synastry partners tend to help each other with essentially any problems and challenges life can throw; unless the combination is negatively afflicted. If Mercury is damaged in either horoscope, the partners are likely to nag, carp, and find faults with or without reason. If, however, the aspect is positive, the relationship has a great chance to be lasting, reliable, and cover a lot of areas of the partners’ intellectual and creative work.
from F. Sakoyan, L. Ecker
Mercury in 6th House Synastry Explained
The sight of you working will likely delight a Mercury in 6th House synastry partner so much that he or she may postpone their own business to start chatting and even give you an advice or two as to what you should be doing and what you should avoid. Now, their intentions may be innocent and having nothing but your best interest in mind; but the effect could be the opposite as you’ll feel slighted and highly irritated.
If a Mercury in Sixth House synastry partner is (1) clever enough, and (2) puts some effort into understanding the nature of your work, it’s possible that some of his or her findings will be relevant and applicable. Reaching this level, however, may take some time while any superficial discussions (albeit likely to distract you from the original course of action) will hardly lead to any positive gains.
The main thing for you and your Mercury in 6th House synastry partner to understand (and the sooner it’ll happen, the better for both of you) is that your work and their chit-chat are incompatible even when it seems to them that you are the one initiating the chit-chat. A more effective approach to improving this synastry is using the partner’s mental and communication skills; the challenge here is that, for this, the partner will need to accept a subordinate role and carry out your requests and orders precisely. A possible (positive) side-effect of such a partnership could be an improvement of the partner’s own Mercury. In general, this synastry is best symbolized by the Medieval relationship between a master and his apprentice.
from A. Podvodny