hey woody, i think of it like working out...although the penis is not a muscle it can be trained in the same way. A good physique must be maintained by a solid exercise and dietry regime. With hair medication if you want to keep what you have and improve on it you have to keep taking it.
As with jelquing etc..you will see gains (i have recently with jelquing) but you should keep up the regime in order to maintain your gains. Even if its at a lower intensity to keep the gains you have made.