Are you sure that it was SV?
https://www.gov.uk/guidance/security-vetting-and-clearance
"
There are 3 security levels:
- Counter Terrorist Check (CTC): is carried out if an individual is working in proximity to public figures, or requires unescorted access to certain military, civil, industrial or commercial establishments assessed to be at particular risk from terrorist attack
- Security Check (SC): determines that a person’s character and personal circumstances are such that they can be trusted to work in a position which involves long-term, frequent and uncontrolled access to SECRET assets
- Developed Vetting: (DV) in addition to SC, this detailed check is appropriate when an individual has long term, frequent and uncontrolled access to ‘Top Secret’ information. There is also Enhanced DV
"
So more likely SC or DV?
A while since I looked at this and they keep changing the names; I think the lowest check used to be Basic Check or BC.
Regardless, I don't know of any reason that T2 controlled by pills (but which pills?) should affect security clearance.
Perhaps you could tell us what medication you are on?
It is possible that if you are on a medication which carries the risk of hypoglycemia there are certain duties (including but not only driving) which might cause issues. For example being sole person on site out of hours.
In which case it would be an operational thing (like working a crane or driving a forklift) and not a security clearance thing.