I dunno. I wasn't stupid enough to retain my fertility, so I can't test this; BUT. . .this stuff makes you go on the rag. Chicks have done it in the past with various other poisons. Sometimes they live, sometimes not. But hey! Ain't death better than bein' forced to take care of one of those disgusting parasites? Assume this works better if you like do it a day or two after getting laid, as opposed to waiting a few weeks, and I wonder if it would even work after a month? I suspect this is 'like morning after' stuff, provided it is efficacious.
Oil of oregano, and this stuff is actually good for you. But go easy on it. Don't do it in pure form, but dilute it in olive oil, and it only takes a few drops. The stuff is HARSH! Google it.
Castor beans. Toxic, and you may wish you were dead for a while on a non-lethal dose, but hey. How many? I dunno. Maybe tennish? The toxin is over rated from what research I've done, I assume soil quality has something to do with ricin content of each seed so dosage may vary, and if you value your life I suppose this isn't the best theoretical way; provided it even works. Again, I can't verify this by using myself as a subject. Google this too, if you even wanna go there.
There is a Yoga exercise. Bend over and put your hands on your knees. Exhale EVERYTHING. Flit you stomach muscles in and out as hard as you can for maybe about 3 minutes. NO, don't hold your breath for 3 minutes, but just stop, breath, exhale, and do it again. Do it in mid-cycle if you don't mind goin' on the rag again in 12 days or whatever. Just to prove it to yourself. I don't think this is on the web.
And of course you can check the web for other theoretical ways. Maybe the oil of oregano and the Yoga exercise combined it the best way to go?
Oh, and why not check this blog out:
http://angryforareason.blogspot.com/2006/02/how-to-induce-miscarriage-herbally-and.html
It might be better than my stuff.