While I somewhat agree with CatherineZeta and Alice the Goon, I don’t think I’d be so extreme as to officially ‘drop’ them by telling them as much. I would just stop initiating contact.
I have had two types of friends ‘use me’ that seem somewhat forgivable. In the first case, that person had two kids in rapid succession and their life turned upside down. As a result, any time spent with them is me having to go to their house 100% of the time and hang out on their schedule. Most of the time, they don’t have the time or money to go out, even for fast food, unless I pick it up and bring it to their house. When they do have time/money, our ‘hanging out’ time always involves at least some “come run errands with me” activity. I don’t enjoy that, but accept that I have to compromise if I want the friendship to last, which I do, because this is a long time friend, and when the kids get older, this will be less of a problem.
The other one is a work friend from a previous job. He always got paid a lot less than me, and shortly after I left the company because I knew layoffs were coming, he got laid off. We used to hang out and try new restaurants, but he has been an independent contractor for the last year and money is extremely tight. About 90% of the time when we hang out now, it is to do some near zero-cost thing (like hiking), where I have to drive and eat the cost of gas. Or it seems to be me solving some problem in his life that is usually, a “how do I fix this broken thing that usually costs money, but that I want you to fix for me for free?” thing. Again, this is not particularly fun for me. What really annoys me about this, though, is he always springs the “fix my broken stuff” thing on me when I am out with him, rather than asking me in advance, so that I can bring the proper tools to do the job. This always necessitates a second visit just to fix the thing, though I know he knows he is going to ask once I am there. I have mentioned this to him several times and all he can do is apologize that he doesn’t think of it at the time.
Not hearing from either friend in a month is not uncommon, though increasingly more so with the second friend, who is on thin ice since he doesn’t have kids as an excuse. Either way, I would just let the friendship naturally fizzle out rather than taking an active role to end them.
The only time I have taken a quasi-active role was when I had friends (almost always this was a mutual friend of both myself and my wife) who would ask us to do favors for them, but would never reciprocate. The classic was the “could you watch my dog, as I’m going out of town” thing. Even then, after a while I would be passive aggressive and simply lie and say we couldn’t do it when they’d ask, while still asking them to watch our dog at various times. Eventually, they would get pissed off and say “hey, you never watch my dog!”, and I would remind them of all the times we had, at which point they would usually dump me as a friend when they discovered they couldn’t use me.