"Toxin X is a substance that will make you violently ill for a few hours. However, it has no long term effects of any kind. As an experiment in psychology, I'm offering you a million dollars if tonight at midnight you fully intend to drink toxin X by tomorrow at noon. You don't actually have to drink the toxin; all you have to do is to intend to drink it. Your intention will be tested by a device similar to a polygraph which my people have developed and which has been shown to be 100% accurate. If at midnight you have the intention, a million will be wired to your bank account. The only other conditions are that you are to make no bets, do anything that will cause you to become irrational, or arrange for any way to avoid the effects of the toxin."

Suppose you decide that being ill for one day is a reasonable price to pay for a million dollars. Your first thought is to therefore agree to the proposal. It then occurs to you that you won't even have to become sick in order to win the money. All you have to do is to intend to drink the toxin. You don't actually have to carry out your intention.

But now if you know ahead of time that you don't actually have to drink the toxin, then you can't really intend to drink it. So you tell yourself you really do have to drink it. But then if at midnight you really did intend to drink the toxin, and you got the million, then come the next day you would no longer have any reason to drink it: you've already been paid and drinking the toxin would make you unnecessarily sick.

Is there any way for you to win the money?

The erason thwe paradox exists in this problem is because the definition of 'intend' is nebulous and fleeting.  You can have an intention without committing yourslef to that intent, and an intention can have a lifetime that spans picoseconds.

As stated the problem requires the intend to exist at midnight.  Because intentions are fleeting, when the clock strikes midnight the intent may or may not be there.  If the problem had stated that the intent had to exist some time before midnight the paradox would not exist.

Another way of removing the paradox would be to change the problem to state that all you had to do was picture yourself drinking the poison at midnight.  The act of imagining drinking the poison is as nebulous as 'intent' so the paradox goes away.