Opiate Habituation (Not As Sordid As It Sounds)

How much, and how frequently, does one have to use a (mild) opiate before habituation (i.e., diminished efficacy/tolerance/need for higher doses to achieve same therapeutic effect) sets in?

Specifically – this is not about daily trips to the shooting gallery. Rather, I’m trying to decide between recommending use of real prescribed codeine cough syrup, “phol-codeine” (obtained from a complaisant pharmacist in Europe), and OTC cough suppressant. The cough (as I can attest, given that I work next to the guy) is horrible, loud, persistent (2 weeks, though it seems like ages longer to me), and not indicative of anything worse than a lingering bad cold or the like (per his MD, who prescribed the codeine). Of course, I am not soliciting (or dispensing) medical advice per se; just looking for generic thoughts on how quickly habituation side-effects kick in for these type of meds., so regard it as a hypothetical if you will.

I’m of the “don’t use the big guns unless you have to” school of thought (and have already persuaded him to ditch the MD-prescribed broad spectrum antibiotics, given that his strep culture was negative and I enjoy practicing medicine w/o benefit of license). I can’t honestly recommend the OTC cough stuff, as I have never seen it work to any degree (decongestants and expectorants OTC do seem to be of some help with the underlying mucus problems, sometimes). Codeine works like a charm for the tickle/hacking, but . . .

So – will using, say, a few teaspoons of codeine-containing syrup a few times a day over a couple of weeks cause any appreciable habituation?

If so, does the tolerance disappear or diminish upon cessation, and how quickly, or can the required effective dose be permanently increased?

Does “pholcodeine” work at all (how well, if so?), and is its supposed “nonhabituating” quality illusory (a la methadone)?