So about the bottle vs the pills— both of those meds are benzodiazepines, which are what Langdon is a user of. We are meant to pick up through context clues what happened with the bottle. Langdon had prescribed it to an earlier patient, took some of it for himself, topped it up with water/saline, then glued the lid shut and put it back in the dispenser claiming it went unused. That is then the bottle that Santos struggles to open, and when it is opened and used the patient requires a unusually high amount of it (because it’s been diluted) which Langdon insists is normal— he gets angry at Santos for questioning it and blames her inexperience. What Santos shows Robbie with the bottle during their conversation is that it’s been resealed using medical glue.
It’s a fun little mystery how much of this is Santos lucking into observations due to her ego being bruised vs how much is knowing the signs of med tampering & stealing vs how much is her spidey senses about addiction (lots of hints about her being familiar with drug users + she just did a rotation in a pain clinic).
IMO this tampering is far worse than just straight up taking the pills, as it’s putting diluted meds into the supply where patients could be seriously harmed by not getting a strong enough dosage.