Well, honestly mebendazole is a very useful drug for most of the worms (parasites) but few need other kind of medications to be killed and eradicated from your body.
If you are sure that you are passing worms (not food material resembling worms) in your stools, then the sample should be repeated. This is the first step in the management as unless the specific kind of worm is identified a specific and targeted management plan can not be instituted.
As per standard guidelines, at least 2 sets of stool samples have to be sent to the laboratory in order to analyze this with certainty. It is not only the worms, but also the eggs and ova of the parasites which help in establishing the diagnosis.
Once identified and diagnosed, it will be easy for the doctors to give you the most useful drug to treat this.
These are few other useful medications that can be used.
So your next step is to get a consultation with an Internist in your area and make sure that your stool samples are studied by a parasitologist (which your doctor can help find one) who can diagnose this with certainty.
I would have been worried too if I were at your place, but let me reassure you that this is a treatable condition and carries a good prognosis with appropriate management.
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