@John&Rose were denied a K-1 for a similar situation, but in their case, they did not disclose an arrest and it was discovered by USCIS in the background check if I remember correctly.  So if you disclose the mistake and provide all documentation for these two criminal records, DUI and drug related, it might help your case.  But whatever you do, disclose it, as US immigration does look look favorably on lying on immigration forms.  If you do not disclose this and it is found by US immigratio