Technically google results say don't use it if it's missing the foil seal. Could be contaminated or something I guess.
But is an open bottle of cough syrup spoiled? Nah, not really.. they sit in cupboards for years and once in a while someone uses some. Still works, doesn't go rotten because it's basically syrup. Over many years it might spoil/lose it's potency.
If it's a new bottle you just bought then it's Probably supposed to come with a foil "safety seal," so you know it hasn't been tampered with. Up to you if you want to use it or return/exchange it. Recommendations from the manufacturer say don't use it - because they have to cover their ass and give the safest instructions. Up to you if you want to use it. Maybe it just didn't get a seal from the factory.. maybe someone tampered with it. No way to know for sure and only you can decide if the risk that it's no good is acceptable to you or not.
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No
![Heart :heart:](./images/smilies/icon_heart.gif)
for supporting trump. Because doing so is deplorable.