In terms of treatment... in bipolar you're in luck! There're drugs and they actually, for most people, work.

In terms of BPD, you're screwed! (sarcasm) No drugs!

That's the short answer ---------

The longer answer follows and simply consists of some information and comments regarding Borderline Personality Disorder.

Basically Borderline Personality Disorder, like all personality disorders listed in the big books of mental "illnesses" (ie. the DSM 5 and the ICD-10-CM), is more about an ingrained way of being that was learned early in life; is nearly reflexive in nature; is very difficult to unlearn and highly resistant to change. It, like other personality disorders, is also almost always characterized by "poor insight" - that is to say have you ever met a narcissist who said "Oh wow, maybe I'm not perfect?"

An earlier poster mentioned DBT (Dialectical Behavioral Therapy) which is the current "gold standard" of care for BPD. It was first proposed by a, imho, rather brilliant woman named Marsha Linehan in her book Cognitive Behavioral Treatment of Borderline Personality Disorder, Guilford Press 1993. Basically DBT is Cognitive Behavioral Therapy "including elements of acceptance and mindfulness with a touch of Zen."

In her book, Linehan wrote that people with Borderline Personality Disorder were most assuredly not responsible for getting themselves into their mess but were unfortunately solely responsible for getting themselves out.

BPD is often characterized by attention seeking behavior, often from medical or mental health providers as a result of the fact that healthcare professionals are obligated to provide services in certain circumstances, and also in reality because nobody in those businesses wants to get sued if someone turns up dead as a result of a parasuicidal act (a sort of 'half-hearted' suicide attempt whose goal - whether consciously or unconsciously - is NOT death but is in fact a desire to garner attention). Commonly person's with BPD will have a history of self-mutilation / harm and a history of unsuccessful suicide attempts.

As a result, in cases where patients with BPD continually access services in order to gain attention which they cannot get elsewhere, DBT involves "contracting" with a therapist when it comes to things like showing up on time for appointments; calls to a therapist's office; agreeing not to commit suicide; etc. For example, a DBT client might be precluded from calling a therapist more than once every week or even two weeks, and the time limit would roll over each time a therapist is called.

BPD is a difficult personality disorder to treat. As a previous poster indicated, it is theorized that it is born out of childhood traumas and difficulties in maintaining appropriate attachments. Basically the theory is that it's like praising a puppy for peeing on the floor then beating it for obeying a command to sit. Then the next time you beat it for peeing on the floor and praise it for sitting. When the puppy (to be read PERSON) gets older and pees on the floor and isn't rewarded for it they get all confused because they thought that's what they were supposed to do. As a result, people expressing symptoms of BPD often have difficulty choosing appropriate emotional responses to their feelings / environments and look to other for cue / clues for what to do in order to get their needs met.

That's WAY oversimplified, but it's apt. People expressing symptoms of Borderline Personality Disorder, again it is theorized, learned maladaptive behaviors as kids and bring them with them all along their life course. They "split" (black and white thinking - "you love me" one moment, "you hate me" the next); they often form inappropriate emotional attachments very quickly when people pay attention to them (either positive or negative), then just as quickly cast them aside when people get exhausted from having to constantly reinforce their need for praise, acceptance, attention.

Therapists who work with clients suffering from Borderline Personality Disorder, if they are really using the DBT handbook, themselves have therapists. This is in part to ensure the therapist is keeping the therapeutic process on course, but is also to ensure the therapist isn't getting burnt out by the client.

Typically, unless it's in an inpatient setting or with a therapist who specializes in Borderline Personality Disorder and Dialectical Behavioral Therapy, a therapist will only agree to see one or two clients expressing BPD symptoms at a time before referring out. Real DBT requires very specialized training, usually in teams, and oftentimes therapists will simply refer out clients with BPD due to the reality that it is beyond the scope of their area of practice

Clients exhibiting Borderline Personality Disorder can be exhausting for therapists, both empathetically draining as well as in the sheer amount of time and resources which have to be devoted to people with such needs.

The reasons for this should by now be obvious.

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So, that about sums up the "short version" of Borderline Personality Disorder beyond the criterion.

You can see similarities I suppose. If someone were bipolar and, for example, rapid cycling between manic and depressed they could be going from "you love me like all the stars in the sky" to "you hate me don't you?"

Key differences are usually found in doing a complete biopsychosocial history, especially looking for parasuicidal and self-harming behaviors as well as a history of rocky and unstable, often very rapid, emotional attachments / breakups. Oftentimes a history of childhood abuse (mental, sexual, physical) will also be among the list of things found in clients expressing Boderline traits.

Currently there are no known drug therapies for treating Borderline Personality Disorder. According to the National Institute of Mental Health:

...many people with borderline personality disorder are treated with medications in addition to psychotherapy. While medications do not cure BPD, some medications may be helpful in managing specific symptoms. For some people, medications can help reduce symptoms such as anxiety, depression, or aggression. Often, people are treated with several medications at the same time, but there is little evidence that this practice is necessary or effective.