My take, based on my knowledge of neurotransmitters and receptors, would be that nootropics that have an acute effect (e.g. Adderall) would be likely to cause downregulation with regular use. For most nootropics with a cumulative effect (e.g. bacopa, EPA/DHA), downregulation is unlikely since the direct effect isn't neurotransmitter increase or receptor agonism. For some of the nootropics with a broader accute effect (e.g. piracetam), occasional cycling couldn't hurt.
My personal approach is to cycle off non-cumulative nootropics when I don't need them (school breaks, etc), and use acute ones only as needed. For the ones that show benefits with extended use, I use year-round with the intent of lifelong benefit. I'm trying to avoid downregulation over time, so that when I do need a boost, I can get a big one easily. Also, only using some of the more expensive ones as needed is cheaper.
This is the best response here, I think. It really depends on the substance in a huge way.
As for piracetam, I think it's necessary to cycle as well. I try to take at least a day or two off every week, and for longer periods when I don't need such intense concentration. Unfortunately, I also feel like efficacy is a lot more hit-or-miss, so maybe just longer breaks would work better. It helps to have other non-racetam options to use during breaks, if you really need nootropics to do what you want/need. There are probably some longer threads here wherein you can find more opinions, but unfortunately I don't think it's possible to get very specific about the best cycle schedule, and it depends a lot on how it works best with your individual factors.
Edited by chrono, 17 November 2011 - 06:26 AM.