I think all medications have the ability to alter a persons personality, some are much more prone to it than others, and narcotics are certainly included in this.
It is often more difficult for the person to see himself as easily as others do, so his/her perspective could be a bit shaded. I can see how a person may feel narcotics change the way they act, the key is using them for the right reasons, in the correct dosage and only as needed under a doctors care.
I have an illness that requires me to have pain control, and I am under the care of a pain specialist. My family has noticed that I am the same exact person, only pain free. I have not done anything unusual or acted out in any way. I do not feel impaired or desire to take any medication out of turn, too early or in higher dosages.
That is my experience, but everyone is different. I have other serious illnesses that require me to take medications the rest of my life, and the pain medication is just one of them. Wishing you the best!