Best to vary your workouts

DEAR DR. ROACH: I recently read that swimming is considered the “perfect exercise.” Do you agree? — R.C.

ANSWER: My experience with people who write that one exercise is the best (or the most difficult) is that they often choose the one they like best. For the vast majority, the best exercise for you is the one you will keep doing, since pretty much any exercise is better than none.

Swimming is great exercise: It works many muscle groups and has outstanding cardiovascular effects. It’s easy on the joints, which is a major benefit for some.

However, it doesn’t provide as much benefit to your bones as higher-impact exercise. It doesn’t provide the balance benefits of yoga or tai chi. But if you like to swim, then swim!

You can get additional benefit from other exercises, including walking, which may be the easiest exercise for most.

DEAR DR. ROACH: You wrote recently that thyroid medication is regulated to within 5 percent of the stated amount.

Are there other drugs that are similarly regulated?

Are generic manufacturers held to a different standard than the manufacturers of brand-name drugs? — A.L.S., M.D.

ANSWER: The Food and Drug Administration continues to work on new standards for drugs that are considered “narrow therapeutic index,” meaning the dosages have to be precise, due to the fact that these drugs can be more than usually toxic at a high dose or that the consequences of too low a dose also are more dangerous than other drugs.

These drugs include anti-epilepsy drugs, some other psychiatric medications, drugs to prevent rejection of transplanted organs and thyroid medication and digoxin.

(The Board of Pharmacy of North Carolina lists 11 drugs it considers to have a narrow therapeutic index.) I know that an internal group at the FDA has recommended implementing the same 95 to 105 percent standard for all these types of drugs.

For thyroid medication, all manufacturers, whether brand-name or generic, are required to meet the same standards.

DEAR DR. ROACH: I have peripheral neuropathy due to a pinched nerve. I get some relief from it, but it still hurts and keeps me from sleeping. My doctor recommended a Tylenol PM, and it helps me sleep well for six or seven hours most nights.

But some nights I wake up hurting and have trouble getting back to sleep.

Then I can take two regular Tylenol and, most nights, get back to sleep after about 30 minutes.

My concern is the long-term use of the Tylenol PM. — W.H.

ANSWER: Tylenol PM contains both acetaminophen (the pain reliever in plain Tylenol) and diphenhydramine (an antihistamine with sedating qualities).

Both of these components have some potential for harm, which must be balanced against the benefit you are getting from them.