Is ADHD a disability?

My husband is seeing a new psychiatrist, who may not know anything about ADD. When my husband was describing his ADD symptoms the doctor said "you are disabled" but my husband is working and wants to continue to do so. The doctor took him off anti-depressants, which we think is a mistake. The theory seems to be that the anit-depressants keep the ADD meds from working right. But Wellbutrin is often prescribed for ADD, so we don't understand how that could be keeping the Concerta from working. The doctor seems to be saying that the anti-depressants are the reason why he seems to build up a tolerance to the meds after about 6-9 months, and then it's like he's taking no ADD meds at all.

My questions for the smart members of this forum: Is ADD a disability? I'm afraid that label will keep my husband from trying to fix things.

Has anyone heard this theory that anti-depressants make ADD worse? What does he do about it if the doctor is wrong. We have limited funds to keep paying the co-pays.