Are there diseases for which a placebo treatment is state of the art?
Doctors sometimes use "open-label placebos" - substances that have no known physiological effect on the treated disease, but have been associated with symptoms improvement in some studies. Open-label means doctors openly tell people it's placebo. The example is treatment of irritable bowel syndrome.

Doctors use not only fake drugs, but also real drugs as placebos. There are some doctors who don't have a courage to say they don't know how to help, so they just prescribe "something" (a real but ineffective drug) in the hope they will convince someone that they provided some help.

Prescribing "placebo treatments": results of national survey of US internists and rheumatologists (BMJ, 2008)


  Prescribing placebo treatments seems to be common and is viewed as
  ethically permissible among the surveyed US internists and
  rheumatologists. Vitamins and over the counter analgesics are the most
  commonly used treatments. Physicians might not be fully transparent
  with their patients about the use of placebos and might have mixed
  motivations for recommending such treatments.


There is a common practice to prescribe:


Vitamins or antibiotics for common cold, flu and other viral infections (Montana DPHHS ; JRSM Open)
Antipsychotics, antidepressants and sedatives for personal problems that can't really help to solve those problems
Various drugs for fibromyalgia


The seeming effect of placebo can discourage a person to seek for the real treatment.