Complex sentence: Modern tests can thus readily tease out whether it was heroin, should someone try to claim he merely ate poppy seeds though there is no way to distinguish between poppy seeds and any other kind of opiate.
Split into simpler sentences: Modern tests can thus readily determine whether it was heroin, should someone try to claim he merely ate poppy seeds. There is, however, no way to distinguish between poppy seeds and any other kind of opiate.