There is a possibility that the accused has nothing to do with it, you still have to prove it wasn't some third party or the victim who procured and took the drug.
Let me clarify. I meant the following. Assume ghb is found and evidence of sex. The woman claims she didn't take it and didn't want to have sex. Wouldn't this be enough for a conviction?
if the jury believed the woman's claims, yes, it's enough for conviction. conviction rates are high not because it's easy to prove guilt, but because district attorneys don't bring case that are likely to be lost. the scenario you describe might not be considered strong enough to win, and resources are limited, so this hypothetical case might not get a hearing.
There is a possibility that the accused has nothing to do with it, you still have to prove it wasn't some third party or the victim who procured and took the drug.