The first thing that comes to mind is over-qualification for specific jobs. It is not usual people with several Masters’ degrees are repeatedly turned down for jobs due to overqualification. Usually boss do not want to hire employees that are more educated than they are. If you feel like the job you are applying for does not need a Ph.D. level of Education to do, it might be safer to omit that from your résumé.

The second problem is the high opportunity costs followed by a sense of no or little progression, e.g., lost income, reduced sense of progression while your friends get promoted/married, and less money than most peers even upon graduation. Many people have a reduced sense of advancement due to the high costs incurred during Ph.D. Having one in itself ultimately doesn’t have a downside in this aspect, but completing one creates many such perceptions.

Your mental health can potentially get in trouble as well… Common mental health problems of someone in the Ph.D. Program or who graduated with a Ph.D. are not unusual. Chronic depression, addiction to alcohol, anxiety or even Imposter Syndrome are mental health problem some PhDs struggle with daily. PTSD is also another factor among PhDs.

You will have frenemies and a difficult social life. People around you (especially those NOT in Ph.D. Programs who don’t understand the background of a Ph.D. Program) will have this “Love/Hate Relationship” with you. They admire that you got a “Doctor” title, but at the same time, they are intimidated by you because you have a Doctor title. If you are not careful with the things you say and do, the surrounding people can negatively judge you and even socially isolate you because things you say or do, if negative, may define you as an arrogant narcissist just because you have a Ph.D. Degree.

The major downside is being “unemployable.” As a person with a master’s degree, you have choice and flexibility, which is absent once you get a doctorate. Most firms would instead hire a master’s degree holder, pay him less and train him more than employ a Ph.D. holder, who would need to be paid more.

Permanent head damage is also one of the downsides of a Ph.D. After using your head too much or only thinking in a certain way, your brain is never the same. You are programmed to think in specific ways. Also, you lose interest in many subjects as you only live and breathe mostly your research topics.

The narrow view is another downside we can think of. You are an expert in a field and mainly focus on those areas and techniques applied there. You get tunnel vision which is not good. You can try to fight it by reading more broadly, but it’s hard. Then, for some people, getting a Ph.D. might give them an inflated ego and sense of superiority, which is never good.