It has no effect on your eligibility for unemployment benefits: if you leave voluntarily (resign) you cannot get them, and you also can't get them if fired "for cause" (such as drugs). It has no effect on whether the employer will report the alleged drug use to the police. Possibly, if you agree to resign, the employer may agree in turn to do something for you, like give you at least a neutral (as opposed to negative) recommendation to a future prospective employer so if you can negotiate something, it's worth resigning, but legally, it will make no difference.