It's easy to consider a search for weapons as reasonable, but TSA also searches for narcotics, unlicensed media, valuables (like diamonds) and just about anything remotely illegal. It's obviously unreasonable to search without probable cause for items not relevant to the safety of a flight. The fourth amendment allows for specific searches, not general searches. And TSA is doing a general search.

TSA will take actions if medication is not in it's original, labeled container. I.e. if you take a few prescription meds or even aspirin out of a bulky bottle and put it in a ziplock to travel with, TSA has discretion to presume guilt, and treat you like a drug trafficer. (this is why you are offered a chance to buy OTC drugs in tiny sealed OEM containers at the airport at extortionate prices).