The present invention generally relates to compositions and methods for transdermal drug delivery. The compositions can be used in a variety of applications, including treating erectile dysfunction or sexual dysfunction, treating wounds, or causing or promoting hair growth. For example, in one aspect, the present invention is generally directed to compositions for delivery of nitric oxide, transdermally and/or to a mucosal surface. The composition may include nitric oxide. The nitric oxide may be present within a first phase comprising a lecithin, such as phosphatidylcholine. In certain embodiments, the lecithin is present in liposomes, micelles, or other vesicles containing nitric oxide. The composition can take the form of a gel, a cream, a lotion, an ointment, a solution, a solid “stick,” etc., that can be rubbed or sprayed onto the skin, e.g., onto the penis, vulva, or other suitable portion of the skin. The composition can also be applied to a mucosal surface in some instances. In some embodiments, a composition comprising nitric oxide is unexpectedly stable and can be stored long-term. Thus, for example, a composition of the invention may exhibit a long shelf life, with little loss or reaction of nitric oxide. This may be particularly useful for certain applications such as consumer products, including those described herein. Other aspects of the present invention are generally directed to methods of making or using such compositions, methods of promoting such compositions, kits including such compositions, or the like.
