Hello and welcome to HCM.
Thank you for your query.
Although there is no direct study proving that metoprolol
can lead to an immuno-compromised state in an individual consuming it. You should note that cold
sores have found to appear when an individual is not healthy (low on immunity, infection, etc.).
As you have mentioned a state of recovery from a cold, this could be the reason for the appearance of the cold sores, as you are in a weaker general state.
Please get these sores checked, and attain adequate treatment for the cause.
I hope I have succeeded in providing the information you were looking for. Please feel free to write back to me for any further clarifications. I would gladly help you.