For me, Modafinil mainly tends to decrease desire. The main mode of action is on alpha 1 adranergic receptors. This doesn't cause problems similar to strattera (I only say this cause I heard other people talk about it) but still can probably cause an issue for some people. Unlike Strattera, which mainly works thru an inhibitory mode of action, Modafinil works thru a different mechanism. It doesn't seem to really increase norepinephirine as significantly as it mainly just stimulates the adranergic receptors for the most part (sensitizes them).
Dopamine, which Modafinil is said to potentiate to some degree, doesn't always necessarily increase sexual desire either since alot of dopamine converts into norepinephirine. The effect on desire (that dopamine does provide) mainly seems to be increased drive/motivation (not necessarily feelings of attachment, bonding, or arousal) which may effect desire for certain types of people.
To increase sexual desire, a balanced endocrine system is big. The HPA axis (Hypothalamus-Pituitary-Adrenal connection) can be disrupted by drugs like modafinil. Male hormone testing (which I've never had the need to do) or adrenal testing (I have done this) can be a great thing to get hormones+neuroendocrine peptides/transmitters back in balance. If something from here is out of balance, taking a drug like modafinil could decrease desire I'm guessing.
Edited by yowza, 22 April 2009 - 12:44 AM.