just me bit lost,
I think I know what you're getting at, but you could try using one sentence at a time to say one thing at a time. It's not a rule, but it would help me, for one!
Claire might recognise the drug from the time she was kidnapped by Ethan. In 'Maternity Leave', she was told it was a vaccine against the sickness on the island.
What she doesn't know, but we do, is that Desmond was using the same vaccine when he was living in the Swan hatch. He grabbed a load of it before he ran off in 'Orientation'.
I think the likeliest explanation is that, so long as the numbers keep being entered, 'someone' knows that there are people inside the Swan who need to be supplied. There wouldn't be much point arranging a parachute drop just for one case of vaccine, so they'd just bung it in with the regular food drop.
What's weird is that a vaccine only needs to be taken once - then you're body gains immunity from the disease. Claire might not realise this, but if she asked Jack, he'd know.
So the 'vaccine' could be a preventive medicine (like anti malaria tablets), could be nothing (another psychological trick?), or it could be a harmful drug (the one that made Claire more compliant in 'Maternity Leave').
At least she knows it didn't do her any long term physical harm, and hasn't (apparently) harmed Charlie. But it could still be unwise to use it: it might be an addictive substance, or it might only work on infants.
THE OWLS ARE NOT WHAT THEY SEEM