In message .com,
jjc001 writes
I have read most of the messages regarding drilling into concrete
lintels above a window and saw the recommended various tools (SDS drill
etc) but one post has a comment stating that this can weaken the lintel
and cause structural damage. Anyone have any experience of these
problems?

No, but obviously in principle drilling holes into lintel will
potentially weaken it.

But for a few small holes to mount a curtain track etc. then I can see
that that is going to really weaken the lintel.
--
Chris French