Acupuncture in general is not painful. The needles are extremely thin (about the width of 2 human hairs), solid, disposable and flexible.
Sensations that patients normally experience are a dull ache or tingling which is associated with the movement of energy stimulated by the insertion of the needles. This is a desired affect and should not feel painful.
The type of acupuncture that I practice is Japanese-style acupuncture, also known as meridian style. This style tends to be what I call a lighter style than traditional Chinese acupuncture. The needles are thin (36# to 40# gauge) and less of them are used during a treatment.
A patient often doesn’t feel the needles go into the point area or, if they do, the sensation is very gentle and the patient’s awareness is much less strong than with the Chinese style. Needles are either taken out directly after insertion or they are left in from a few minutes to 40 minutes.