The present invention generally relates to systems and methods for monitoring and/or providing feedback for drugs or other pharmaceuticals taken by a subject. In one aspect, the present invention is directed to devices and methods for determining a species within the skin of a subject； and producing feedback to a subject based on the determination of the species. The feedback may be, for example, visual, audible, tactile, a change in temperature, etc. In some cases, information regarding the determination of the species may be transmitted to another entity, e.g., a health care provider, a computer, a relative, etc., which may then provide feedback to the subject in some fashion. In some cases, the feedback may be directly indicative of the species, e.g., whether the species is present, the concentration of the species, whether a by-product of a reaction involving the species is present, whether a compound affected by the species is present, etc. However, the feedback may also be indirect in some embodiments. For example, the subject may be presented with an external reward, e.g., based on the determination of the species within the skin. For instance, a reward such as cash, coupons, songs, discounts, personal items, etc., may be offered based on the level of compliance of the subject. Still other aspects of the invention are generally directed to kits involving such devices (with or without the drug to be monitored), methods of promoting such systems, or the like.
