The patient had been on oral contraceptives until 2006; she stopped the Ortho Tri-Cyclen when her husband had his vasectomy.

This is a run-on that requires a period after 2006.
This is a run on sentence that requires a comma and a conjunction after 2006.
This is a fragment that requires a verb after patient.
This is a fragment that requires a subject.
The sentence is fine as it is.

Read this aloud. Then let us know what you think.

The patient had been on oral contraceptives until 2006; she stopped the Ortho Tri-Cyclen when her husband had his vasectomy.

This is a run-on sentence that requires a period after 2006.

To determine if a sentence is a run-on or not, we need to identify whether multiple independent clauses are connected without proper punctuation. In this case, the phrase "she stopped the Ortho Tri-Cyclen when her husband had his vasectomy" is an independent clause, which means it could stand on its own as a separate sentence. However, it is joined with the previous clause "The patient had been on oral contraceptives until 2006" without any punctuation to separate them.

To correct the run-on sentence, we need to insert a period after 2006, creating two separate sentences. This would clarify the meaning and improve readability.