Well assuming you are in the US your best bet would be an anti-histamine. I would recommend doxylamine, I?ve read that it is as sedating as phenobarbital. It?s used as an OTC sleep-aid. Other than that Benadryl or it?s generic diphenhydramine would be another option as it is an anti-histamine and does has some sedative properties. You can always look into a substance called Phenibut. You can find it online pretty cheap. But as for OTC substances at the pharmacy your best bet will be anti-histamines. You can look into herbal substances like kratom and kava kava. Each one of these options has their own positives and negatives and they are all different compounds with different effects, durations of action, etc. If you persue any of these things please take the time to educate yourself!