The bar in Great Dover Street is popular with students and student societies. KCL student newspaper Roar has reported on the alleged incidents.
A statement posted on the bar's Instagram page says: "To all our customers who have been affected by last weekend's incidents, we are deeply sorry that this has happened and we hope you are safe and well."
The bar says it will be upgrading its CCTV equipment, working with the relevant authorities and conducting random searches to deter people from bringing drugs into the premises.
The venue is advising customers to avoid accepting drinks from people they don't know or trust, not to leave drinks unattended and to alert staff to any suspicious behaviour.
"We value and care for each of our customers and we are committed to ensuring every individual is safe and able to enjoy their Dover Castle experience."