Steve- I have the feeling that we are talking about two entirely different drugs here? What you call DM is that "Dextromethorphan"? I am talking about Dextroamphetamine, which is related to methamphetamine. The two are VERY different in structure and CNS activity.
Anyhoo, the salient points to be hammered home about Dextroamphetamine is that it is a very potent , quick acting stimulant, and that it has the potential to greatly lengthen the on time, for those who have those "instant" offs that can be both embarrassing AND dangerous. Due to it's highly addicting properties,and it's quick "tolerance" building effect (which means that it takes more and more to produce the initial effects) dextroamphetamine is not a drug that you would want to use every day. The amazing thing about Dextroamphetamine, is that thousands of children take it every day for years to help with ADD (attention deficit syndrome), as the drug called Concerta. Although it is a CNS stimulant, it also has the ability to calm hyperactive children, quite a paradox.
I have never taken well to ANY antidepressant, but dextroamphetamine seems to lift my chronic depression for as long as it's effects last. I accept being addicted to Parkinson's and pain medication; without those drugs life would be intolerable, but i don't have to feel good or be able to do physical things that i can't do normally with Parkinson's, ALL the time, so I can take dextroamphetamine, intermittantly, at my discretion, and with good sense (like a casual drinker), i shouldn't get, "hooked" on it.
I truly believe that DEX-A, CAN BE a useful adjunct drug in PD, though , like evrything, is not for everybody.